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Oracle® Fusion Middleware Language Reference Guide for Oracle Business Rules
11g Release 1 (11.1.1.7)

Part Number E10227-10
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2 Rule Language Reference

This chapter contains a detailed and complete reference to the Oracle Business Rules RL Language (RL Language) syntax, semantics, and built-in functions.

Grammar rules define the RL Language. Each grammar rule defines a non-terminal symbol on the left of the ::= symbol in terms of one or more non-terminal and terminal symbols on the right of the ::= symbol.

Reserved Words

aggregate, boolean, break, byte, catch, char, class, constant, continue, double, else, exists, extends, fact, factpath, false, final, finally, float, for, function, hide, if, import, include, instanceof, int, long, modify, new, null, property, public, query, return, returns, rule, rulegroup, ruleset, short, supports, synchronized, throw, true, try, while, var

Note:

Reserved words in bold apply to the current release. Reserved words that are not shown in bold typeface are planned for a future RL Language release, and include the words: break, continue, and query.

This chapter includes the following sections:


Ruleset

A ruleset groups a set of definitions. A ruleset is a collection of rules and other definitions that are all intended to be evaluated at the same time. A ruleset may also contain executable actions, may include or contain other rulesets, and may import Java classes and packages.

Format

ruleset ::= named-ruleset | unnamed-ruleset

named-ruleset ::= ruleset ruleset-name { unnamed-ruleset }

unnamed-ruleset ::= ( import | include | named-ruleset | definition | action | fact-class | rulegroup)*

ruleset-name ::= identifier

Usage Notes

A named-ruleset creates or adds definitions to the specified ruleset named ruleset-name.

An unnamed-ruleset adds definitions to the default ruleset named main.

Rulesets may be nested, that is they may contain or include other rulesets. Nesting does not affect ruleset naming, but it does affect ruleset visibility in a way similar to Java import's affect on package visibility.

You can execute a ruleset using the RL Language command-line, or using the Java RuleSession API.

A named-ruleset ruleset-name must be unique within a RuleSession.

Examples

Example 2-1 contains two definitions, enterRoom and sayHello, and two actions (assert and run).

The rule shown in Example 2-1 will not fire until:

  1. An enterRoom fact is asserted.

  2. The run function executes, which pushes the rule's containing ruleset, hello onto the ruleset stack.

Example 2-1 Using a Named Ruleset

ruleset hello {
  class enterRoom { String who; }
  rule sayHello {
    if (fact enterRoom) {
      println("Hello " + enterRoom.who);
    }
  }
  assert(new enterRoom(who: "Bob"));
  run("hello");
}

In Example 2-2, if ruleset R2 is nested in ruleset R1, the name R2 must be unique within the rule session. R2 is not named relative to R1. For example, the class C2 defined in R2 is globally named R2.C2, not R1.R2.C2. If R2 is nested in R1, a public class C1 defined in R1 may be referenced in R2 using either the full name R1.C1 or the short name C1 (assuming R2 does not also define C1).

Example 2-2 Using a Nested Ruleset

ruleset R1 {
  public class C1 { 
    public String s;
  }
  C1 apple = new C1(s: "apple");
  ruleset R2 {
    public class C2 { 
      public String s;
    }
    C1 c1 = apple;        // finds C1 and apple in containing ruleset R1
    c1.s = "delicious";
    C2 c2 = new C2(s: "pear");
  }
  R2.C2 pear = R2.c2; // finds R2.C2 and R2.c2 because they are fully qualified
  println(apple.s + " " + pear.s); // prints "delicious pear"
  
  pear = c2;  // UndefinedException: c2 not in R1 or a containing ruleset
}

Types

RL Language is a strongly typed language. Each variable and value has a specified type.

Format

type ::= simple-type [ [ ] ]

simple-type ::= primitive | object-type

primitive ::= boolean | numeric

numeric ::= int | double | float | long | short | byte | char

object-type ::= class-definition-name | Java-class-name

class-definition-name ::= qname

Java-class-name ::= qname

Type Conversion

There are several ways that a value can be converted from one type to another:

  1. Conversion from any type to String using the String concatenation operator + .

  2. Implicitly from context. For example, by adding an int to a double first converts the int to a double and then adds the 2 doubles.

  3. Casting between 2 numeric types.

  4. Casting between 2 classes related by inheritance.

  5. Invoking a function or method that performs the conversion. For example, toString.

Table 2-1 summarizes the implicit conversions for various types. Rows indicate how the type in the From column may be implicitly converted, as shown in the list of types shown in the To column.

Table 2-1 Implicit Type Conversions

From To

int

double, float, long

float

double

long

double, float

short

int, double, float, long

byte

int, double, float, long, short

char

int, double, float, long

String

Object

Object

Object (if the From Object is a subclass of the To Object)

fact set

boolean

array

Object


Note:

An Object is an instance of a Java or RL Language class or array. Type conversion is possible only if the classes are related by inheritance (implements or extends).

Table 2-2 summarizes the allowed cast conversions for various types where a cast can be used to convert a primitive with more bits to a primitive with fewer bits, without throwing an exception.

The type conversions shown in Table 2-2 require an explicit cast operator. For example,

int i = 1;
short s = (short)i;

Note:

Type conversions such as those shown in Table 2-2 that involve numeric types may lose high order bits, and such conversions involving Objects may throw a RLClassCastExeption.

Table 2-2 Explicit Type Conversions

From To

double

float, long, int, short, byte, char

float

long, int, short, byte, char

long

int, short, byte, char

short

byte, char

byte

char

char

byte


When you use a cast to convert a primitive with more bits, to a primitive with fewer bits, the RL Language discards extra, high order, bits without throwing an exception.

For example,

short s = -134;
byte b = (byte)s;
println("s = " + s + ", b = " + b);
prints: s = -134, b = 122

Primitive Types

A primitive type may be any of the following

Object Types

An object type may be:

String Types

RL Language uses Java strings, where:

Array Types

Square brackets [] denote arrays. An array in RL Language has the same syntax and semantics as a Java 1-dimensional array.

Note:

RL Language does not support multi-dimensional arrays.


Identifiers

RL Language supports both the Java and the XML variant of identifiers and namespace packages. To use the XML variant, the identifier must be enclosed in back quotes.

Format

identifier ::= java-identifier | xml-identifier

java-identifier ::= valid-Java-identifier

xml-identifier ::= `valid-xml-identifier or URI `

Where:

valid-Java-identifier is: a legal Java identifier, for example, JLd_0.

valid-xml-identifier is: a legal XML identifier, for example x-1.

URI is: a legal Uniform Resource Identifier, for example, http://www.oracle.com/rules

Usage Notes

An xml-identifier can contain characters that are illegal Java identifier characters, for example, ':' and '-'. The JAXB specification defines a standard mapping of XML identifiers to Java identifiers, and includes preserving the Java conventions of capitalization. The JAXB specification also defines a standard mapping from the schema target namespace URI to a Java package name, and a mapping from anonymous types to Java static nested classes.

Examples

RL Language supports both the Java and the XML variant of identifiers and namespaces or packages. Enclose an identifier in back quotes to use the XML variant, as shown in Example 2-3.

You can use the back quote notation anywhere an identifier or package name is legal in RL Language. To use the XML variant of identifiers in String arguments to assertXPath, back quotes are not needed.

Example 2-3 Sample Mapping for XML Identifiers Using Back Quotes

`http://www.example.com/po.xsd` -> com.mycompany.po
`my-attribute` -> myAttribute
`Items/item` -> Items$ItemType

Literals

Table 2-3 summarizes the RL Language literals. The literals are the same as Java literals.

Table 2-3 RL Language Literals

A literal such as Can be assigned to variables of these types

An integer in range 0..127 or a char with UCS2 encoding in range 0...127

byte, char, short, int, long, float, double

An integer in range 0..65535 or a char

char, int, long, float, double

An integer in range -128..127

byte, short, int, long, float, double

An integer in range -32768..32767

short, int, long, float, double

An integer

int, long, float, double

An integer with L suffix

long, float, double

A floating point constant

double

A floating point constant with F suffix

float, double

A String enclosed in ""

String, Object



Definitions

When a definition within a ruleset is executed, it is checked for correctness and then saved for use later in the rule session.

Format

definition ::= variable | rule | rl-class-definition | function

name ::= identifier

qname ::= [ ruleset-or-packagename. ]name

ruleset-or-packagename ::= qname

Usage Notes

Every definition has a unique name within its containing ruleset, and thus a unique qualified name, qname, within the rule session.

Variables defined at the ruleset level are global. Global variables are visible to all expressions contained in the ruleset using the name of the variable and visible to expressions in other rulesets using the variable qname. Functions and public classes may also be referenced from other rulesets using the respective qname.

Java classes and their methods and properties also have qnames.

Example

The qname of the class definition in Example 2-4 is hello.enterRoom.

Example 2-4 Class Definition Within a Named Ruleset

ruleset hello {
  class enterRoom { String who; }
  rule sayHello {
    if (fact enterRoom) {
      println("Hello " + enterRoom.who);
    }
  }
  assert(new enterRoom(who: "Bob"));
  run("hello");
}

Variable Definitions

Variables are declared as in Java, but initialization is always required.

Format

variable ::= [ final ] ( numeric name = numeric-expression

| boolean name = boolean-expression

| type [ ] name = array-expression | null

| object-type name = object-expression | null )

) ;

Usage Notes

The type of the array initialized with the array-expression must be the same as the type specified for the array elements.

A variable can have a primitive type, a Java class name, or an RL Language class name, and may be an array of elements of the same type.

The type of the object-expression must be the same as the object-type of the variable being declared. A class instance or array may be initialized to null.

Variables may be local or global in scope. The initialization expression is required. Local variables may not be final.

Global Variables

Variables immediately enclosed in a ruleset, that is, in a definition, are global to a rule session in scope. The initialization expression for a final global variable is executed when the global variable is defined.

The initialization expression for a non-final global variable is executed both:

Global variables declared as final may not be modified after they are initialized.

Global variables referenced in a rule condition (fact-set-condition) must be final.

Examples

Example 2-5 shows that the reset function performs initialization for the non-final global variable i. Thus, this example prints 0, not 1.

Example 2-5 Non-Final Global Variable Initialization After Reset Function

RL> int i = 0;
RL> i++;
RL> reset();
RL> println(i);

Be careful when initializing global variables with functions that have side effects. If you do not want the side effects repeated when calling reset, you should declare the variable final. For example, Example 2-6 prints "once" twice and Example 2-7 prints "once" once.

Example 2-6 Initializing a Global Variable with Side Effects with Reset

RL> clear;
RL> function once() returns int
{ 
  println("once");
  return 1;
}
RL> int i = once();
once
RL> reset();
once
RL>

Example 2-7 Initializing a Final Global Variable to Avoid Side Effects with Reset

RL> clear;
RL> function once() returns int
{ 
  println("once");
  return 1;
}
RL> final int i = once();
once
RL> reset();
RL>

Rule Definitions

The Oracle Rules Engine matches facts against the fact-set-conditions of all rules in the rule session to build the agenda of rules to execute. A fact set row is a combination of facts that makes the conditions of a rule true. An activation is a fact set row paired with a reference to the action-block of the rule. The agenda is the list of all activations in the rules session. The Oracle Rules Engine matches facts and rules when the state of working memory changes, typically when a fact is asserted or retracted.

The run, runUntilHalt, and step functions execute activations. Activations are removed from the agenda after they are executed, or if the facts referenced in their fact set row are modified or retracted such that they no longer match the rule's condition.

Activations are executed in order of the ruleset stack. You can manage the ruleset stack with the getRulesetStack, clearRulesetStack, pushRuleset, and popRuleset functions.

In order for a rule to fire, three things must occur:

  1. An activation of that rule must be on the agenda.

  2. The containing ruleset must be at the top of the ruleset stack.

  3. You must invoke run, runUntilHalt, or step.

The fact set produced in a fact-set-condition is available to the rule actions. For each row in the fact set, the action-block is activated as follows:

Format

rule ::= rule rule-name { property* fact-set-condition action-block }

rule-name ::= name

property ::= priority | autofocus | logical | active

priority ::= priority = numeric-expression

autofocus ::= autofocus = boolean-literal

logical ::= logical = ( boolean-literal | positive-integer-literal )

active ::= active = boolean-literal

effectiveDateForm ::= effectiveDateForm = an int restricted to one of values defined in oracle.rules.rl.Rule: EDFORM_DATE, EDFORM_DATETIME, or EDFORM_TIME

effectiveStartDate ::= effectiveStartDate = expression of type java.util.Calendar

effectiveEndDate ::= effectiveEndDate = expression of type java.util.Calendar

Where:

positive-integer-literal is: an integer literal that is > 0

Usage Notes

The priority property specifies the priority for a rule. Within a set of activations of rules from the same ruleset, activations are executed in priority order (see "Ordering Rule Firing"). When rules have different priorities, the rules with a higher priority are activated before those with a lower priority. The default priority is 0. Within a set of activations of rules of the same priority, the most recently added activations are executed first, but this behavior can be changed (see the getStrategy and setStrategy functions).

A rule with the autofocus property equal to true automatically pushes its containing ruleset onto the ruleset stack whenever it is activated.

A rule with the logical property makes all facts asserted by the rule's action block dependent on some or all facts matched by the rule's condition. An integer value of n for the logical property makes the dependency on the first n top-level &&ed fact set expressions in the rule's condition. A boolean value of true for the logical property makes the dependency on the fact set expression of the condition. Anytime a fact referenced in a row of the fact set changes such that the rule's logical conditions no longer apply, the facts asserted by the activation associated with that fact set row are automatically retracted. A rule with the logical property enabled makes all facts that are asserted by an action block in the rule dependent on facts matched in the rule condition. Anytime a fact referenced in the rule condition changes, such that the rule's conditions no longer apply, the facts asserted by the rule condition are automatically retracted.

The active property defaults to true.

effectiveStartDate date defaults to null.

effectiveEndDate date default to null.

effectiveDateForm defaults to Rule.EDFORM_DATETIME

Examples

Example 2-8 shows a rule with the inference, Socrates is mortal, which depends on the fact, Socrates is a man.

Example 2-8 Defining and Using Rule allMenAreMortal

RL> clear;
RL> class Man    {String name;}
RL> class Mortal {String name;}
RL> Mortal lastMortal = null;
RL> rule allMenAreMortal {
  logical = true;
  if (fact Man)
  {
    assert(lastMortal = new Mortal(name: Man.name));
  }
}
RL> watchAll();
RL> Man socrates = new Man(name: "Socrates");
RL> assert(socrates);
 ==> f-1 main.Man (name : "Socrates")
==> Activation: main.allMenAreMortal :  f-1
RL> run();
Fire 1 main.allMenAreMortal f-1
 ==> f-2 main.Mortal (name : "Socrates")
 <== Focus main, Ruleset stack: {}
RL> retract(socrates);
 <== f-1 main.Man (name : "Socrates")
 <== f-2 main.Mortal (name : "Socrates")
RL> showFacts();
f-0   initial-fact()

Example 2-9 shows that it is possible for the same fact to be asserted by multiple rules, or to be asserted by a top-level ruleset action or function. Such a fact will not be automatically retracted unless all asserters have logical clauses that call for automatic retraction. A fact that is asserted by a top level action or function will never be automatically retracted.

Note that the fact that Socrates is mortal is not retracted, because it was asserted by a top level action that is not dependent on the fact that Socrates is a man.

Example 2-9 Asserting Facts Unconditionally

RL> assert(socrates);
 ==> f-3 main.Man(name : "Socrates")
==> Activation: main.allMenAreMortal :  f-3
RL> run();
Fire 1 main.allMenAreMortal f-3
 ==> f-4 main.Mortal(name : "Socrates")
 <== Focus main, Ruleset stack: {}
RL> assert(lastMortal);
 <=> f-4 main.Mortal(name : "Socrates")
RL> retract(socrates);
 <== f-3 main.Man(name: "Socrates")
RL> showFacts();
f-0   initial-fact()
f-2   main.Mortal(name: "Socrates")

Class Definitions

All referenced classes must be defined with an RL Language class definition or must be on the Java classpath (Java classes must be imported).

Both RL Language classes and Java classes can support xpath using the supports keyword, with a supplied xpath.

Format

rl-class-definition ::= [ public ] [ final ] class name [ extends ] [ supports ] { type-property* }

type-property ::= [ public ] type name [ = expression ] ;

extends ::= extends qname extended-class-name

extended-class-name ::= qname

Usage Notes

The type of the optional initialization expression must be the same as the type of the property or implicitly convertible to that type.

A public class is visible from all rulesets. A non-public class is visible only in the containing ruleset.

A final class cannot be extended.

The extended class must be a defined RL Language class not an imported Java class.

Each property may have an optional initializer. The initializer is evaluated when the class is instantiated by new. If an initial value is also passed to new, the value passed to new overwrites the value computed by the initializer in the class definition.

A public property is visible from all rulesets. A non-public property is visible only within its containing ruleset.

Examples

In RL Language, the type of an property may be the name of the containing class definition (see Example 2-10). RL Language, unlike Java, does not support forward references to class definitions (see Example 2-11).

Example 2-10 Class Definition with Type of Property with Name of Containing Class

class C0 {
  C0 next;
}

Example 2-11 Class Definitions with Forward References are Not Allowed

class C1 {
  C2 c2;  // causes an UndefinedException
}
class C2 {
  C1 c1;
}

xpath Support

Note:

xpath support has been deprecated. For more information, see assertTree.

Both RL Language classes and Java classes support xpath.

An XML identifier does not need to be surrounded by back quotes within an xpath.

The built-in assertXPath function supports a simple xpath-like syntax to assert a tree of objects as facts. The nodes in the tree are objects from classes in the same package or ruleset that support xpath. The links between parent and child nodes are instances of the XLink class. All of the properties in a class that supports xpath may be used in the xpath expression.

Format

supports ::= supports xpath

xpath ::= first-step next-step*

first-step ::= ( . | /* | [ // ] ( identifier | * ) ) predicate*

predicate ::= [ identifier xrelop literal ]

next-step ::= ( / | // ) ( identifier | * ) predicate*

xrelop ::= eq | lt | gt | le | ge | ne | == | < | > | <= | >= | !=

literal ::= integer-literal | decimal-literal | double-literal | string-literal | true | false | dateTime-literal
| date-literal | time-literal

integer-literal ::= [-] d+

d ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

decimal-literal ::= [-] ( . d+ | d+ . d*)

double-literal ::= [-] ( . d+ | d+ [ . d* ] ) ( e | E ) [+ | -] d+

string-literal ::= " char* " | ' char* '

dateTime-literal ::= local-date T time-literal

date-literal ::= local-date [ time-zone ]

time-zone ::= Z | ( + | - ) d d : d d

local-date ::= d d d d - d d - d d

time-literal ::= d d : d d : d d [. d+] [ time-zone ]

Usage Notes

RL Language xpath support was designed to work with classes that conform to the Java XML Binding (JAXB) 1.0 standard. All JAXB elements from the given root to the elements selected by the xpath, inclusive, are asserted. Additional XLink facts are asserted to aid in writing rules about the parent-child relationships among the asserted elements.

If a JAXB element is retracted or re-asserted, using assert, then all of its children, and XLinks, are retracted. Instead of re-asserting, use assertXPath again.

Note that RL Language Xpath is not a proper subset of W3C Xpath 2.0. Note the following differences:

Examples

Table 2-4 shows the xpath selection options for use with the built-in assertXPath function. In the descriptions, select means that the element is asserted as a fact, and the selected property of the XLink whose element property refers to the asserted element is true. The ancestors of a selected element, up to and including the root element, are always asserted, but not necessarily selected.

Table 2-4 xpath Selection Strings

xpath Select String Description of Selection

//*

Select all elements including the root

.//*

Select all but the root

.

Select only the root

//foo

Select all objects that are the value of a property named foo.

.[x==1]/y

Select children or attributes of root named y only if the root has a child element or attribute named x and equal to 1


Example 2-12 instantiates an RL Language class called Person to build a family tree, as follows:

First Generation   Second Generation     Third Generation
Ida
                   Mary
                                          Fred
                                          John
                   Rachel
                                          Sally
                                          Evan

Example 2-12 uses the assertXPath function twice, with two xpaths:

//kids[male==true]
//kids[male==false]

Example 2-12 defines two rules:

Example 2-13 shows the output from running Example 2-12.

Example 2-12 Sample Family Tree Rule Using supports xpath

import java.util.*;
ruleset xp {
  public class Person supports xpath {
    public String name;
    public boolean male;
    public List kids;
  }
        // Build the Family Tree
  Person p = new Person(name: "Fred", male: true);
  List k = new ArrayList();
  k.add(p);
  p = new Person(name: "John", male: true);
  k.add(p);
  p = new Person(name: "Mary", male: false, kids: k);
  Person gramma = new Person(name: "Ida", male: false, kids: new ArrayList());
  gramma.kids.add(p);
  p = new Person(name: "Sally", male: false);
  k = new ArrayList();
  k.add(p);
  p = new Person(name: "Evan", male: true);
  k.add(p);
  p = new Person(name: "Rachel", male: false, kids: k);
  gramma.kids.add(p);
  // test for siblings.
  // Note the test id(p1) < id(p2) halves the Cartesian product p1 X p2.
  rule sibling {
    if (fact Person p1 && fact Person p2 && id(p1) < id(p2) &&
        exists(fact XLink(element: p1) x && 
               fact XLink(element: p2, parent: x.parent))) {
      println(p1.name + " is sibling of " + p2.name);
    }
  }
  // test for brothers and sisters, given the following 2 assertXPath() calls
  rule brotherSister {
    if (fact Person p1 && fact Person p2 && id(p1) < id(p2) &&
        exists(fact XLink(element: p1, selected: true) x && 
               fact XLink(element: p2, selected: true, 
                          parent: x.parent) y && 
               x.samePath(y))) {
      println(p1.name + " and " + p2.name + " are " +
              (p1.male ? "brothers" : "sisters"));
    }
  }
  assertXPath("xp", gramma, "//kids[male==true]");
  assertXPath("xp", gramma, "//kids[male==false]");
  run("xp");
}

Example 2-13 Output from Run of Family Tree Example

Mary and Rachel are sisters
Evan is sibling of Sally
Fred and John are brothers
Fred is sibling of John
Mary is sibling of Rachel

Example 2-14 shows that when you retract an element that was asserted with assertXPath, all its descendents are retracted as well.

The result is:

f-0   initial-fact()

For a total of 1 fact.

Example 2-14 Retract the Family Tree

retract(xp.gramma);
showFacts();

Example 2-15 prints all pairs of ancestors. First, the family tree is asserted. Example 2-16 shows the output of a run of the code from Example 2-15.

Example 2-15 Print Ancestor Pairs with Class Ancestor

assertXPath("xp", xp.gramma, "//*");
class Ancestor { Object element; Object ancestor; }
rule parents {
  if (fact XLink x) {
    assert(new Ancestor(element: x.element, ancestor: x.parent));
  }
}
rule ancestors {
  if (fact XLink x && fact Ancestor(ancestor: x.element) a) {
    assert(new Ancestor(element: a.element, ancestor: x.parent));
  }
}
rule printAncestor {
  if (fact xp.Person p && fact xp.Person a && 
      fact Ancestor(element: p, ancestor: a) {
    println(a.name + " is an ancestor of " p.name);
  }
}
run();

Example 2-16 Output from Run of Ancestor Example

Mary is an ancestor of John
Ida is an ancestor of John
Mary is an ancestor of Fred
Ida is an ancestor of Fred
Ida is an ancestor of Mary
Rachel is an ancestor of Evan
Ida is an ancestor of Evan
Rachel is an ancestor of Sally
Ida is an ancestor of Sally
Ida is an ancestor of Rachel

Function Definitions

A function is similar to a Java static method.

Format

function ::= function name parameters [ returns type ] action-block

parameters ::= ( [ type identifier ( , type identifier )* ] )

Usage Notes

The action-block may invoke the function being defined. However, the action-block may not contain a forward reference to a function that has not already been defined (see Example 2-17 and Example 2-18).

Functions may be overloaded. For example, the built-in println function is overloaded.

Examples

Example 2-17 Valid Function Definition Containing Recursive Reference

function factorial(long x) returns long {
  if (x <= 1) { return 1; }
  else { return x * factorial(x - 1); }
}

Example 2-18 Invalid Function Definition Containing Reference to Undefined Function

function f1() {
  f2();  // causes an UndefinedException
}
function f2() {
}

Fact Class Declarations

Any Java class can be used as an RL Language fact in a fact context.

A fact context is one of:

If a class or interface B implements or extends class or interface A, and both A and B appear in fact contexts, then A must appear before B. Failure to follow this rule will result in a FactClassException.

Fact class definitions are not required when using RL Language classes.

For xpath support, use the supports xpath clause of the RL Language class definition.

Format

fact-class ::= fact class class-name [ supports ] ( fact-class-body | ; )

class-name ::= qname

fact-class-body ::= { [ hidden-properties | properties ]}

hidden-properties ::= hide property * ; | ( hide property ( ( name , )* name | * ) ; )+

properties ::= property * ; | ( property ( ( name , )* name | * ) ; )+

Usage Notes

The fact-class-body is optional in a fact-class declaration. The default fact-class-body is:

{ property *; }

Either the property or hide property keywords can be used in a body, but not both.

If hide property is used with a list of property names, then those property names are hidden and not available for use in RL Language.

If hide property is used with the wildcard "*", then no properties other than those exposed by a superclass or superinterface are available for use in RL Language.

If property is used with a list of property names, then those properties are exposed and available for use in RL Language. If property is used with the wildcard *, then all properties other than those hidden by a superclass or superinterface are available for use in RL Language.

A HiddenPropertyException will be thrown if a superclass exposes a property that its subclass hides or if a subclass exposes a property that its superclass hides.

Examples

Suppose a Java class Vehicle has subclasses Car and Truck. The rule shown in Example 2-19, matchVehicle, generates a TypeCheckException wrapping a FactClassException because the subclasses are referenced before the superclass. Wrapping is used instead of subclassing for both FactClassException and MultipleInheritanceException because in some fact contexts, these exceptions are not thrown until runtime and then are wrapped by a RLRuntimeException.

Example 2-19 matchVehicle Rule with Subclasses Referenced Before the Superclass

assert(new Car());   // fact context for Car
assert(new Truck()); // fact context for Truck
rule matchVehicle {
  if (fact Vehicle v) { // fact context for Vehicle - too late!
    if (v instanceof Car) {
      println("car");
     } else {
      println("truck");
     }
   }
 } // generates a TypeCheckException wrapping a FactClassException

In Example 2-20, the matchVehicle rule is the first reference to the superclass, so no exception is thrown.

Example 2-20 matchVehicle Rule with References to Superclass First

clear;
rule matchVehicle {
  if (fact Vehicle v) {
    if (v instanceof Car) {
      println("car");
     } else {
      println("truck");
     }
   }
 }
assert(new Car());
assert(new Truck());
run();  // prints "truck" then "car"

In Example 2-21, a fact class declaration is the first reference to the superclass, so no exception is thrown.

Example 2-21 matchVehicle Rule with Fact Class Declaration with Reference to Superclass First

clear;
fact class Vehicle;
assert(new Car());
assert(new Truck());
rule matchVehicle {
  if (fact Vehicle v) {
    if (v instanceof Car) {
      println("car");
     } else {
      println("truck");
     }
   }
 }
run();  // prints "truck" then "car"

Facts do not support multiple inheritance. Consider the Java classes and interfaces shown in Example 2-22.

Example 2-22 Java Classes and Sample Multiple Inheritance

package example;
public class Car {}
public interface Sporty {}
public class SportsCar extends Car implements Sporty {}

Example 2-23 entered at the command-line results in a TypeCheckException that wraps a MultipleInheritanceException. Use the getCause method on the TypeCheckException to retrieve the wrapped MultipleInheritanceException exception.

Example 2-23 MultipleInheritance Exception for Facts

import example.*;
fact class Sporty;
fact class Car;
fact class SportsCar; // throws TypeCheckException wrapping a MultipleInheritanceException

Example 2-24 illustrates an exception that occurs at runtime when the Oracle Rules Engine attempts to assert the rx8 object and discovers its true type is SportsCar, not Object. To avoid the MultipleInheritanceException, you must choose whether to use Sporty or Car in a fact class context. You cannot use both.

Example 2-24 RLRuntimeException wraps MultipleInheritanceException

import example.*;
fact class Sporty;
fact class Car;
Object rx8 = new SportsCar();
assert(rx8);  // throws RLRuntimeException wrapping a MultipleInheritanceException

Example 2-25 FactClassException Possible Cause

oracle.rules.rl.FactClassException: fact class for 'X' should be declared earlier in rule session

Note the fact context rule is:

If X is a subclass or subinterface, of Y, then Y must appear in a fact context before X. A fact context is a fact-class declaration, a rule fact pattern, or the argument of assert, assertXPath, or retract.

In some cases you need to consider the fact context. For example, with an XML schema such as the following:

<schema>
  <element name=A type=T/>
  <complexType name=T>
    <sequence>
      <element name=B type=T/>
    </sequence>
  </complexType>
</schema>

JAXB generates:

interface T {
  List getB();  // List has TImpl objects
}
interface A extends T;
class AImpl implements A extends TImpl;
class TImpl implements T;

In an example with the following order of appearance in fact contexts:

  1. fact class T

  2. assertXPath AImpl

  3. assert TImpl (performed internally by the assertXPath implementation)

The, AImpl precedes TImpl in the ordering, yet AImpl extends TImpl, which would give the exception. The fix for this fact context is to explicitly issue fact class TImpl; anywhere before Step 2.


Import Statement

An import statement makes it possible to omit the package name qualification when referencing Java classes.

Format

import ::= import ( Java-class-name | Java-package-name.* ) ;

Java-package-name ::= qname

Usage Notes

Import commands can be placed inside a ruleset, implying that the scope of the import is the ruleset where the import is located, but the import actually applies globally. For example, in the following code if the imports were scoped to the rulesets, then the PrintWriter reference in r2 would not compile.

class X { }

ruleset rl {
  import java.io.*; 
  rule A {
  if ( fact X ) {
@ PrintWriter pw = null;
  }
} 
} 

ruleset r2 { 
  rule B {
    if ( fact X ) {
      @ PrintWriter pw = null;
    }
  }
}

Include Statement

Include the ruleset at the location specified by the URL.

Format

include ::= include URL ;

Where:

URL is: A legal Uniform Resource Locator.

Usage Notes

The file: and http: schemes are supported.

Example

include file:example.rl;

Using Expressions

Expressions in RL Language use familiar Java syntax (with minor variations as noted). For example,

(a + 1) * (b - 2)

Use expressions in a condition or in an action, with some restrictions. Expressions are strongly typed.

Format

expression ::= boolean-expression

| numeric-expression

| string-expression

| array-expression

| fact-set-expression | object-expression

| comparable-expression


Boolean Expressions

Boolean expressions, as in Java, may be either true or false.

Format

boolean-expression ::= boolean-assignment

| boolean-expression ? boolean-expression : boolean-expression

| boolean-expression || boolean-expression

| boolean-expression && boolean-expression

| numeric-expression equal-op numeric-expression

| object-expression equal-op object-expression

| boolean-expression equal-op boolean-expression

| object-expression instanceof type-name

| numeric-expression relop numeric-expression

| string-expression relop string-expression

| ! boolean-expression

| boolean-primary-expression

boolean-assignment ::= boolean-target-expression = boolean-expression

equal-op ::= == | !=

relop ::= < | > | <= | >=

type-name ::= qname

Usage Notes

For strings, < is Unicode UCS2 code point order.

For objects,!= does not test for inequality of object references, but rather is the negation of the equals methods.

Thus, the statement:

if (object1 != object2){}

Is equivalent to the statement:

if (! (object1.equals(object2)){}

RL Language, unlike Java, does not support testing for equality of object references.

Example

Example 2-26 shows use of a boolean expression in RL Language.

Example 2-26 RL Boolean Expression

if (
  (true ? "a" < "b" : false)
  && (1 == 0 || 1.0 > 0)
  && "x" instanceof Object )
{
  println("all true");
};

Numeric Expressions

Numeric expressions, as in Java, implicitly convert integer operands to floating point if other operands are floating point. Table 2-1 shows other implicit conversions.

Format

numeric-expression ::= numeric-assignment

| boolean-expression ? numeric-expression : numeric-expression

| numeric-expression( + | - ) numeric-expression

| numeric-expression ( * | / | % ) numeric-expression

| numeric-expression ** numeric-expression

| ( numeric-cast ) numeric-expression

| ( + | - ) numeric-expression

| ( ++ | -- ) numeric-primary-expression

| numeric-primary-expression [ ++ | -- ]

numeric-assignment ::= numeric-target-expression ( = | += | -= | *= | /= | %= ) numeric-expression

numeric-cast ::= numeric

Usage Notes

Table 2-5 shows the precedence order, from highest to lowest, for a numeric-expression.

Table 2-5 Expression Operator Precedence

Symbols Category Description

++
--

Post-increment or Post-decrement

numeric-primary-expression [ ++ | -- ]

++
--

Pre-increment or Pre-decrement

( ++ | -- ) numeric-primary-expression

-
+

Unary minus or
Unary plus

( + | - ) numeric-expression

(type)

Type cast

( numeric cast ) numeric-expression

**

Exponentiation

numeric-expression ** numeric-expression

*, /, %

Multiply or Divide or Remainder

numeric-expression ( * | / | % ) numeric-expression

+ , -

Addition or Subtraction

numeric-expression( + | - ) numeric-expression

 

Conditional

boolean-expression ? numeric-expression : numeric-expression

=

Assignment Operators

numeric-target-expression ( = | += | -= | *= | /= | %= ) numeric-expression



String Expressions

As in Java, any expression can be converted to a string using the concatenation + operator. In RL Language, unlike Java, when an array is converted to a string, the array contents are converted to a string, with array elements separated by commas and surrounded with curly braces. When an instance of an RL Language class is converted to a string, the class name appears followed by property value pairs separated by commas and surrounded with parentheses. This RL Language feature is useful for logging, tracing, and debugging.

When + operator is applied to an operand that is a String, then all operands are converted to Strings and the operands are concatenated.

Format

string-expression ::= string-assignment

| boolean-expression ? string-expression : string-expression

| string-expression + expression

| expression + string-expression

| string-primary-expression

|

string-assignment ::= string-target-expression ( = | += ) string-expression

Example

Example 2-27 shows use of a string expression in RL Language. The example prints "1 2.0 true {1,2}"

Example 2-27 RL String Expression

int i = 1;
double f = 2.0;
boolean b = true;
int[] v = new int[]{i, 2};
println(i + " " + f + " " + b + " " + v);

Array Expressions

RL Language arrays behave just like Java arrays, but are limited to one dimension. The base type of an array is the type of the members of the array. All members must be of the same type. An array element may contain an array but only if the containing array is of type Object[].

Note:

RL Language does not directly support multi-dimensional arrays.

Format

array-expression ::= array-assignment

| boolean-expression ? array-expression : array-expression

| ( array-cast ) ( array-expression | object-expression )

| array-primary-expression

array-assignment ::= array-target-expression = array-expression

array-cast ::= type

Usage Notes

The type of an array-cast must be an array type.


Fact Set Expressions

A fact-set-expression matches, filters, and returns facts from working memory. A fact-set-expression is legal only in a rule fact-set-condition. The if keyword indicates a fact-set-condition; however, a fact-set-condition is different from an if action. A rule's fact-set-condition iterates through all the rows in a fact set that match the fact-set-condition. The if action tests a boolean expression.

Format

fact-set-condition ::= if fact-set-expression

fact-set-expression ::= fact-set-expression || fact-set-expression

| fact-set-expression && fact-set-expression

| fact-set-expression && boolean-expression

| ! fact-set-expression

| exists fact-set-expression

| fact-set-pattern

| (fact-set-expression)

| aggregate

fact-set-pattern ::= fact [ ( property-pattern ( , property-pattern )* ) ]

[ var ] local-object-variable

local-object-variable ::= identifier

property-pattern ::= property-name : field-pattern

field-pattern ::= var local-property-variable | constraint

local-property-variable ::= identifier

simple-expression ::= string literal

| object-target-expression

| numeric literal

| numeric-target-expression

| boolean-literal

| boolean-target-expression

constraint ::= simple-expression

property-name ::= name

aggregate ::= aggregate fact-set-expression : aggregate-spec ( , aggregate-spec )*

aggregate-spec ::= aggregate-function [ var ] identifier

aggregate-function ::=

average ( numeric-expression )

| sum ( numeric-expression )

| minimum ( comparable-expression )

| maximum ( comparable-expression )

| count ()

| collection ( object-expression )

| user-defined ( expression type Tin )

user-defined ::= qname

Usage Notes

A fact-set-expression can limit the facts it returns using either a simple-expression as a constraint in a fact-set-pattern or using a supported operator with the fact-set-expression.

A fact-set-expression may not contain any of the following:

Operator precedence is as in Java. Use parentheses to force desired precedence. For example,

fact person var p && (p.age < 21 || p.age > 65)

Without the parentheses, the p in p.age is undefined (see Table 2-5 for more details on operator precedence).

A local-object-variable or local-property-variable is in scope for all expressions following the pattern that are following the pattern and connected with the && operator. If the pattern is not contained in an exists, ||, or ! expression, the variable is also in scope in the rule's action-block. The &&'ed expressions may filter the returned facts, so that only the facts surviving the filter are returned.

Fact Set Pattern - Fetch From Working Memory

The most primitive fact-set-expression is the fact-set-pattern that returns some or all facts of the given class that have been asserted into working memory. A fact-set-pattern searches working memory for facts of the given class and with the optional constraint on the property values. The returned fact set contains a row for each matching fact. A local row variable can be defined to refer to each row, or local field variables can be defined to refer to fields within a row. If no local row variable is supplied, the name part of the class qname can be used to refer to each row (see Example 2-31).

Join Operator

The && operator defines the cross product or join of two fact-set-expression operands. The left-hand-side of a fact-set-expression && operator must be a fact set. The right-hand-side of a join operator is another fact-set-expression. The result of applying the && operator to two fact sets is the joined fact set.

Filter Operator

The && operator defines a filter operator that rejects facts in its left-hand-side fact-set-expression that do not match the right-hand-side boolean-expression. The left-hand-side of filter must be a fact-set-expression. The right-hand-side of a filter is a boolean-expression.

A filter right-hand-side may include references to variables defined, using the var keyword, in the left-hand-side.

Union Operator

The || operator defines the union of two fact-set-expression operands. When the|| operator is applied to fact-set-expressions, the following is true:

Note:

In the following construction:

if (fact X || fact W) {}

If both an X and a W are asserted, this rule fires twice, one time for each fact.

Empty Operator

The ! operator tests if the fact-set-expression is empty. When the ! is applied to the fact-set-expression, the following is true:

Exists (Not Empty) Operator

The exists operator tests if the fact-set-expression is not empty.

When the exists operator is applied to the fact-set-expression, the following is true:

Var Keyword

Note that when you use var, the fact is only visible using the var defined variable (and not using the original name). Thus, the following example works, assuming action.kind is defined:

if (fact action) {
   println(action.kind);
}

However, for the following example, after var a is defined, the action.kind reference produces a syntax error because you need to use a.kind after the var a definition.

if (fact action var a) {
  println(action.kind);
}

Aggregate

Aggregates support the following functions:

Table 2-6 Aggregate Functions

Function Description

average()

Provides the average for matching facts. The result is double.

sum()

Provides the sum for the matching facts. The result is double or long.

count()

The result is long.

minimum()

Provides the minimum for the matching facts.

maximum()

Provides the maximum for the matching facts.

collection()

The result is java.util.List of Facts.

user defined

For a user-defined function the result is type Tout.


RL Language supports the aggregate pattern that applies one or more aggregate functions to a factRowCollection, and binds the aggregates to pattern variables. The usual SQL set of built-in aggregates is supported, and user-defined aggregates are supported when a user-supplied Java class is supplied.

If an aggregate function uses primitive wrapper types, for example Long, Double, then these will be unboxed such that the bind variable for the result has the appropriate raw primitive type.

If the fact expression in an aggregate is empty, then the rule will not fire. This ensures that if there are no matching facts for the expression, the aggregate function does not return a number that is meaningless in this context. For example, the "sum" of a property of a zero-size set is not meaningful.

For example, print the names of employees who are paid better than average:

if fact Emp emp && aggregate fact Emp(salary: var sal) : average(sal) var avgSal 
&& emp.salary > avgSal {
   println(emp.name);
}

Print the names of employees, who are paid better than the average of employees who make over $100,000:

if fact Emp emp && aggregate fact Emp(salary: var sal) && Emp.salary > 100000 :  average(sal) var avgSal 
&& emp.salary > avgSal {
   println(emp.name);
}

User-defined aggregates are supported by providing a public class named user-defined with a public 0-arg constructor that implements:

public interface IncrementalAggregate<Tin, Tout> extends Serializable
{
        public void initialize();
        public void add(Tin value);
        public void remove(Tin value);
        public Tout getResult();
        public boolean isValid();
}

Implementations must support the following invocation sequence:

new (initialize (add|remove)+ isValid getResult)*

isValid should return true when the result of the user defined aggregate is valid and false otherwise.

Examples

Example 2-28 shows the action is placed on the agenda for all Counter facts with a value of 1.

Example 2-28 Fact Set Expression for Counter.value

class Counter  { int id; int value; }
rule ex1a {
  if (fact Counter c && c.value == 1) 
  { println("counter id " + c.id + " is 1"); }
}

Example 2-29 shows an equivalent way to express the rule from Example 2-28, using a constraint.

Example 2-29 Using a Fact Set Constraint

rule ex1b {
  if (fact Counter(value: 1) c) 
  { println("counter id " + c.id + " is 1"); }
}
assert(new Counter(id: 1, value: 99));
run();  // prints twice, once for each rule

Example 2-30 shows an illegal use of a fact set, because c is used before it is defined.

Example 2-30 Illegal Use of Fact Set

rule ex2 {  
  if (c.value == 1 && fact Counter c)
  { println("counter id " + c.id + " is 1"); }
}

Example 2-31 shows an action is placed on the agenda for all AttFacts with the property a2==0 and without a matching, equal first elements, Counter.

Example 2-31 Using a Fact Set with && Operator for Counter Fact

class AttFact {int a1; int a2;}
rule ex3 {
  if (fact AttFact(a2: 0) && ! fact Counter(id: AttFact.a1))
  { println(AttFact.a1); }
}
assert(new AttFact()); // will match because a1=a2=0
assert(new AttFact(a1: 1, a2: 0));  // will not match
run();  // rule fires once

Example 2-32 shows the condition, if (fact Ca a && fact Cb(v: a.v) b) is interpreted as follows:

Example 2-32 Using a Fact Set with && Operator

class Ca {int v;}
assert(new Ca(v: 1));
assert(new Ca(v: 2));
assert(new Ca(v: 3));
class Cb {int v;}
assert(new Cb(v: 0));
assert(new Cb(v: 1));
assert(new Cb(v: 2));
rule r {
  if (fact Ca a && fact Cb(v: a.v) b) {
    println("row: " + a + " " + b);
  }
}
run();  // prints 2 rows


Comparable Expression

Comparable expressions allow objects that implement java.lang.Comparable to be compared using the ==, !=, <, <=, >, and >= operators. This allows dates to be easily compared. Also, BigDecimal, often used to represent money, can be compared in such expressions.

Format

comparable-expression ::=

qname variable of type implementing java.lang.Comparable | member of type implementing java.lang.Comparable


Object Expressions

The only expression operators for objects are assignment and cast.

Format

object-expression ::= object-assignment | ( ob-cast ) object-expression |
boolean-expression ? object-expression : object-expression

object-assignment ::= object-target-expression = object-primary-expression

ob-cast ::= object-type


Primary Expressions

Primary expressions include assignment targets such as variables, properties, array elements, class members and other tightly binding expression syntax such as literals, method and function calls, and object and fact construction. The syntax is very similar to Java except where noted.

Format

primary-expression ::= array-primary-expression

| string-primary-expression

| numeric-primary-expression

| boolean-primary-expression

| object-primary-expression

array-primary-expression ::=

array-constructor

| function-call returning array

| method-call* returning 1-dim Java array

| ( array-expression )

| array-target-expression

array-constructor ::= new (

simple-type [ numeric-expression integer ]

| numeric [ ] { numeric-expression ( , numeric-expression )* } numeric expression must be implicitly convertible to base

| boolean [ ] { boolean-expression ( , boolean-expression )* }

| object-type [ ] { object-expression ( , object-expression )* }

)

array-target-expression ::=

qname variable of type array

| member of type array

| array-primary-expression base type is Object [ numeric-expression int ]

string-primary-expression ::=

string literal (see "Literals")

| object-primary-expression object is java.lang.String

string-target-expression ::= object-target-expression object is java.lang.String

numeric-primary-expression ::=

numeric literal

| function-call returning numeric

| method-call returning numeric

| array-primary-expression . length

| ( numeric-expression )

| numeric-target-expression

numeric-target-expression ::=

qname variable of type numeric

| member of type numeric

| array-primary-expression base type is numeric [ numeric-expression ]

boolean-primary-expression ::=

boolean-literal

| function-call returning boolean

| method-call returning boolean

| ( boolean-expression )

| boolean-target-expression

boolean-literal ::= true | false

boolean-target-expression ::=

qname variable of type boolean

| member of type boolean

| array-primary-expression base type is boolean [ numeric-expression int ]

object-primary-expression ::=

new class-definition-name ( [ expression ( , expression )* ] argument list )

| new class-definition-name ( [ property-pattern ( , property-pattern )* ] property-value pairs )

| function-call returning Java object

| method-call returning Java object

| object-target-expression

object-target-expression ::=

qname variable of type object

| member of type Java object

| array-primary-expression base type is object [ numeric-expression int ]

function-call ::= qname function name ( [ expression ( , expression )* ] argument list )

method-call ::= object-primary-expression . identifier method name
( [ expression ( , expression )* ] argument list )

member ::= object-primary-expression . identifier member name

Examples

Example 2-33 shows the RL Language literal syntax (which is the same as Java).

Example 2-33 Use of Literals

String s = "This is a string."
int i = 23;
double f = 3.14;
boolean b = false;

Methods and functions can be overloaded. However, unlike Java, RL Language uses a first fit algorithm to match an actual argument list to the overloaded functions.

Example 2-34 shows an example of example of overloading

Example 2-34 Overloading

function f(int i);
function f(Object o);
function f(String s);  // can never be called
 
f(1);        // calls first f
f("a"); // calls second f, because "a" is an Object

new

RL Language classes do not have user-defined constructors. The default constructor initializes properties to their default values. The RL Language new operator permits specifying some property values (this works for Java bean properties, too).

A Java bean property may have a getter but no setter. Such a property may not be modified.

Example

Example 2-35 Initialization Using the New Operator

class C { int i = 1; int j = 2; }
C c = new C();  
println(c); // c.i == 1 and c.j == 2
c = new C(i: 3); 
println(c); // c.i == 3 and c.j == 2
c = new C(i: 0, j: 0);
println(c); // c.i == c.j == 0

Actions and Action Blocks

RL Language, unlike Java, requires action blocks and does not allow a single semicolon terminated action.

Format

action ::= action-block | if | while | for | try | synchronized | return | throw

| assign | incr-decr-expression | primary-action

action-block ::= { ( variable | action )* }

Usage Notes

An action block is any number of local variable declarations and actions. The variables are visible to subsequent variable initialization expressions and actions within the same action block.

In RL Language, unlike in Java, all local variables must be initialized when they are declared. Local variables may not be final.

To exit, you can invoke the System.exit(int) method from within an action.

Example

Example 2-36 Action Block Sample

RL> {
  int i = 2;
  while (i-- > 0) { println("bye"); }
}
bye
bye
RL>

If Else Action Block

Using the if else action, if the test is true, execute the first action block, and if the test is false, execute the optional else part, which may be another if action or an action block.

RL Language, unlike Java, requires action blocks and does not allow a single semicolon terminated action.

Format

if ::= if if-test action-block [ else if | action-block ]

if-test ::= boolean-expression

Examples

Example 2-37 shows an RL Language if else action block. Example 2-38 shows that an action block is required.

Example 2-37 Sample If Else Action

String s = "b";
 
if (s=="a") { println("no"); } else 
if (s=="b") { println("yes");}
else        { println("no"); }

Example 2-38 Illegal If Action Without an Action Block

if (s=="a") println("no");

While Action Block

While the test is true, execute the action block. A return, throw, or halt may exit the action block.

Format

while ::= while while-test action-block

while-test ::= boolean-expression

Usage Notes

RL Language, unlike Java, requires action blocks and does not allow single semicolon terminated action.

Examples

Example 2-39 prints "bye" twice.

Example 2-39 Sample While Action

int i = 2;
while (i-- > 0) {
  println("bye");
}

Example 2-40 Illegal While Action Without an Action Block

while (i-- > 0) println("no");

For Action Block

RL Language, like Java, has a for loop. Using the for action block, the for-init portion executes, then while the boolean-expression is true, first the specified action block is executed then the for-update executes. A return, throw, or halt may exit the action block.

Format

for ::= for ( for-init ; boolean-expression ; for-update ) action-block

for-init ::= variable | for-update

for-update ::= incr-decr-expression | assign | primary-expression

Usage Notes

RL Language does not allow a comma separated list of expressions in the for init or for update clauses (Java does allow this).

Example

Example 2-41 shows RL Language code that converts an int[] to a double[].

Example 2-41 For Action

int[]    is = new int[]{1,2,3};
double[] fs = is; // error!
double[] fs = new double[3];
for (int i = 0; i < is.length; ++i) {
  fs[i] = is[i]; 
}
println(fs);


Try Catch Finally Action Block

Execute the first action block. Catch exceptions thrown during executions that match the Throwable class in a catch clause. For the first match, execute the associated catch action block. Bind the Throwable class instance to the given identifier and make it available to the catch action block. Whether an exception is thrown in the try action block, execute the finally action block, if given.

Uncaught exceptions are printed as error messages when using the RL Language command-line and are thrown as RLExceptions when using a RuleSession's executeRuleset or callFunction methods. The try, catch, and finally in RL Language is like Java both in syntax and in semantics. There must be at least one catch or finally clause.

Format

try ::= try action-block

( catch (class-implementing-throwable identifier ) action-block )*

[ finally action-block ]

class-implementing-throwable ::= qname

Usage Notes

In order to fully understand how to catch exceptions in RL Language, one must understand how the stack frames are nested during rule execution. Rules do not call other rules the way that functions or methods may call functions or methods. Therefore, you cannot use a catch block in one rule's action block to catch exceptions in another rule's action block. Exceptions thrown during rule firing must either be handled by the firing rule's action block, or must be handled by a caller to the run, runUntilHalt, or step functions that caused the rule to fire.

Examples

Example 2-42 shows the try catch and finally actions. The output from running this example is:

exception in invoked Java method 
this is really bad! 
but at least it's over!

Example 2-42 Try Catch and Finally Action Blocks

try {
  throw new Exception("this is really bad!");
} catch (Exception e) {
  println(e.getMessage());        
  println(e.getCause().getMessage());
} finally {
  println("but at least it's over!");
}

Note that RL Language treats the explicitly thrown Exception ("this is really bad!") as an exception from an invoked Java method, and wraps the Exception in a JavaException. The explicitly thrown Exception is available as the cause of the JavaException.


Synchronized Action Block

As in Java, the synchronized action is useful for synchronizing the actions of multiple threads. The synchronized action block lets you acquire the specified object's lock, then execute the action-block, then release the lock.

Format

synchronized ::= synchronized object-primary-expression action-block

Example

Example 2-43 changes the name of a Person object, adding old names to the nicknames, and synchronizes so that a concurrent reader of the Java object who is also synchronizing will see a consistent view of the Person (See Example 2-12 details on the Person bean).

Example 2-43 Synchronized Action

import example.Person;  // this Java bean is defined in example J1
function changeName(Person p, String first, String last) {
  synchronized(p) {
    java.util.Set s = p.getNicknames();
    s.add(p.getFirstName());
    s.add(p.getLastName());
    p.setFirstName(first);
    p.setLastName(last);
  }
  assert(p);
}
Person person = new Person("Elmer", "Fudd", new String[]{"Wabbit Wuver"});
println(person.nicknames.toArray());
changeName(person, "Bugs", "Bunny");
println(person.nicknames.toArray());

Modify Action

Modify updates the named properties using the associated expressions. It also updates the associated shadow fact, if any, and causes rules whose conditions reference the updated properties and evaluate to true to be activated. Rules whose conditions do not reference the updated properties are not activated.

The object argument to modify must be an object that has already been asserted, then the values of that object are updated and network is updated with the slot-specific semantics. The result is the object and the network are consistent.

Format

modify ::= modify (object-expression , property-update ( , property-update )* )

property-update ::= property-name : expression.

Usage Notes

It is common for a fact to have properties that are set or modified by rules. For example, a customer in an application might have a status of "", "silver", or "gold". The status may be set by rules that examine other properties of customer and related facts (such as past orders). It is also common for these computed properties to be used in further rule conditions. For example, give gold customers a 10% discount. A rule that modifies a fact and reasserts it must be careful to add an extra condition so that it does not reactive itself over and over. For example, if the following rule fires once, it will fire over and over:

if fact Customer c && c.pastYearSpend > 1000 {
   c.status = "gold";
   assert(c);
}

You can fix this looping using the following rule definition:

if fact Customer c && c.pastYearSpend > 1000 && c.status != "gold" {
   c.status = "gold";
   assert(c);
}

Example 2-44 prevents the loop but does not activate rules that are looking for gold customers

Example 2-44 Example Showing Bad Rules Programming Practice to be Avoided

if fact Customer c && c.pastYearSpend > 1000 {
   c.status = "gold";
}

Example 2-44 demonstrates bad rules programming practice because it changes the value of the customer object but not the value of the, shadow, customer fact. The modify action lets you modify the object and fact together. Modify also activates rules that test the modified properties but does not activate rules that test non-modified properties.

if fact Customer c && c.pastYearSpend > 1000 {
   modify(c, status: "gold");
}

This rule does not loop because the tested properties and modified properties are disjoint. This rule can be used in an inference to fire subsequent rules that test for status=="gold".

A second rule that illustrates infinite looping is the rule described as follows:

Give Employees earning at least $50,000 a 5% raise.

if Employee emp && emp.sal > 50000 {
   modify(emp, sal: sal * 1.05);
}

Even using modify, this rule will self-trigger because it is testing the same property (sal) that it is modifying, and the test is true after modification. To avoid looping in this case, you could also add a raise property test, as follows:

if Employee emp && emp.sal > 50000 && !emp.raise {
  modify(emp, sal: emp.sal * 1.05, raise: true);
} 

Alternatively, to avoid looping in this case you could also add a fact to handle the raise. For example:

public class RaiseGiven
{
   Employee emp;  // or possibly just an employee ID
}
 if Employee emp && emp.sal > 500000 && !RaiseGiven(emp: emp) {
   modify(emp, sal: sal * 1.05);
   assert(new RaiseGiven(emp: emp));
}


Return Action

The return action returns from the action block of a function or a rule.

A return action in a rule pops the ruleset stack, so that execution continues with the activations on the agenda that are from the ruleset that is currently at the top of the ruleset stack.

If rule execution was initiated with either the run or step functions, and a return action pops the last ruleset from the ruleset stack, then control returns to the caller of the run or step function.

If rule execution was initiated with the runUntilHalt function, then a return action will not pop the last ruleset from the ruleset stack. The last ruleset is popped with runUntilHalt when there are not any activations left. The Oracle Rules Engine then waits for more activations to appear. When they do, it places the last ruleset on the ruleset stack before resuming ruleset firing.

Format

return ::= return [ return-value] ;

return-value ::= expression

If the function has a returns clause, then the return-value must be specified and it must be of the type specified by the returns clause.

Usage Notes

A return action in a rule or a function without a returns clause must not specify a return-value.


Throw Action

Throw an exception, which must be a Java object that implements java.lang.Throwable. A thrown exception may be caught by a catch in a try action block.

Format

throw ::= throw throwable ;

throwable ::= object-primary-expression


Assign Action

An assignment in RL Language, as in Java, is an expression that can appear as an action.

Format

assign ::= assignment-expression ;

assignment-expression ::= boolean-assignment

| numeric-assignment

| string-assignment

| object-assignment

| array-assignment

Example

Example 2-45 shows the use of the RL Language assignment expression. This prints "6 5".

Example 2-45 Assignment Expression

clear;
int i = 1;
int j = 2;
i += j += 3;
println(i + " " + j);

Increment or Decrement Expressions

Increment and decrement in RL Language, as in Java, are expressions that can appear as actions.

Format

incr-decr ::= incr-decr-expression ;

incr-decr-expression ::= ( ++ | -- ) numeric-target-expression | numeric-target-expression ( ++ | -- )

Examples

Example 2-46 shows the use of the RL Language decrement action. This example prints "0".

Example 2-46 Decrement Action

clear;
int i = 1;
--i;
println(i);

Primary Actions

A primary action is a primary expression such as a function call, assert, or Java method call executed for its side-effects. For example, the println function is often used as a primary action.

Format

primary-action ::= primary-expression ;


Rulegroup

A rulegroup provides support for decision table overrides. This supports the following decision table features: the ability for one rule to override one or more other rules

Format

rulegroup ::= rulegroup rulegroup-name { rulegroup-property* ( rule | rulegroup )* }

rulegroup-name ::= identifier

rulegroup-property ::= mutex

mutex ::= mutex = boolean-literal ;

Usage Notes

A rulegroup construct is a top level construct in a ruleset. A rulegroup has an optional boolean property:

Example

Example 2-47 demonstrates the use of rulegroups with the mutex property. Note that r2 and r3 reference the same set of fact types in the same order in the rule condition. This is required within a mutex group. The tests in the patterns can be different. The restriction on the shape of the rule condition in a mutex group extends to its descendent groups. Thus, rules r4 and r5 also must reference the same set of fact types in the same order. Assume that one instance of A and one instance of B have been asserted and that r1, r2, r3, r4 and r5 have activations on the agenda. r3 will fire since it has a higher priority. The activation of r2 will be removed without firing since r2 is in a group with mutex=true. Since group2 is a member of group1, the activations of r4 and r5 will also be removed without firing. Rule r1 will fire. Now, assume that r2, r4, and r5 have activations on the agenda and assume that r4 fires first. The activation for r2 will be remove without firing since any rule in group2 firing mutually excludes both r2 and r3. r5 will fire. It is not mutually excluded since group2 does not have mutex=true.

Example 2-47 Ruleset with Rulegroup with Specified Fact Order of Reference

ruleset set1
{
 rule r1 { ... }
 rulegroup group1
 {
   mutex = true;
   rule r2 { if fact A && fact B ... { ... }}
   rule r3 { priority = 2; if fact A && fact B ... { ... }}
   rulegroup group2
   {
     rule r4 { if fact A && fact B ... { ... }}
     rule r5 { if fact A && fact B ... { ... }}
   }
 }
}

Built-in Functions

This section covers the following RL Language built-in functions:

assert, assertTree, assertXPath, clearRule, clearRulesetStack, clearWatchRules, clearWatchActivations, clearWatchFacts, clearWatchFocus, clearWatchCompilations, clearWatchAll, contains, getCurrentDate, getDecisionTrace, getDecisionTraceLevel, getDecisionTraceLimit, getEffectiveDate, getFactByType, getFactsByType, getRulesetStack, getRuleSession, getStrategy, halt, id, isErrorInRuleConditionSuppressed, object, println, popRuleset, pushRuleset, retract, reset, run, runUntilHalt, setCurrentDate, setDecisionTraceLevel, setDecisionTraceLimit, setErrorInRuleConditionSuppressed, setEffectiveDate, setRulesetStack, setStrategy, showActivations, showFacts, step, watchRules, watchActivations, watchFacts, watchFocus, watchCompilations


assert

Adds a fact to working memory or updates a fact already in working memory based on the properties of the supplied object obj. If the supplied object obj is a Java instance, then properties are Java bean properties defined by an associated BeanInfo class or by the existence of getter and setter methods. If obj is an RL Language class instance, then the properties are the fields of the class.

Format

function assert(Object obj);

Usage Notes

The fact in working memory is a shadow of the supplied object obj, and this shadow contains a copy, clone, or reference to each property prop. If prop is a primitive type, then prop is copied to the shadow. If prop implements the Java Cloneable interface, then a clone, shallow copy, of prop is shadowed. Otherwise, only the reference to prop is shadowed. The more a shadow can copy its object's properties, the better a rule with references to several facts can be optimized.

Note that because == and != when applied to an Object in RL Language always invokes the Object equals method, whether a shadow contains copies, clones, or references is transparent to the RL Language program.

Assert may affect the agenda. Rules whose conditions now return a fact set because of a new fact place activations on the agenda. Activations that test for non-existence of facts, using !, may be removed from the agenda. Updates to facts may affect the agenda. Activations whose rule conditions no longer match the changed facts are removed from the agenda. Rules whose conditions return a fact set because of the changed facts have activations placed on the agenda.

Assert should be used to update the fact in working memory if any part of the obj's state has been updated that could possibly have an effect on a rule condition, unless the obj is a Java bean that supports registering property change listeners, and all that is changed is the value of a bean property.

Examples

Example 2-48 prints, "Pavi has highest salary 65000.0" and Example 2-49 prints, "dept 10 has no employees!".

Example 2-48 Using Assert Function in the highestSalary Rule

class Emp { String ename; double salary; }
                rule highestSalary {
                     if (fact Emp hi && !(fact Emp e && e.salary > hi.salary))

                        {
                           println(hi.ename + " has highest salary " + hi.salary);
                        }
                }
                Emp e1 = new Emp(ename: "Pavi", salary: 55000.00);
                assert(e1); // put in working memory
                Emp e2 = new Emp(ename: "Fred", salary: 60000.00);
                assert(e2);        // put in working memory
                e1.salary += 10000.00;    // Pavi is now the highest paid
                assert(e1);       // MUST re-assert before allowing rules to fire
                run();        

Example 2-49 Using Assert Function in the emptyDept Rule

import java.util.*;
class Dept { int deptno; List emps = new ArrayList(); }
             rule emptyDept {
                  if (fact Dept d && d.emps.isEmpty()) {
                         println("dept " + d.deptno + " has no employees!");
                        }
                }
                Dept d = new Dept(deptno: 10);
                d.emps.add(e1);
                assert(d);         // put in working memory with 1 employee
                d.emps.remove(0);
                assert(d);         // MUST re-assert before allowing rules to fire
                run();

See Also

assertTree, id, object, retract


assertTree

The assertTree built-in function asserts object in an object tree as facts.

The assertTree built-in function supports JAXB 2.0.

Format

assertTree(Object root)

assertTree(String spec, Object root)

Usage Notes

There are two assertTree() signatures:

The assertTree function does the following:

See Also

assert


assertXPath

The assertXPath function is deprecated. Use assertTree instead.

Add a tree of facts to working memory using the specified element as the root and an XML xpath-like expression to define the objects in the tree. The pkg is the Java package or RL Language ruleset that contains the classes of objects in the tree. All objects in the tree must be in the same package or ruleset.

In addition to asserting "element" and selected descendants, XLink facts are asserted that link parent and child objects. The classes of all objects in the tree must use the supports xpath (supports) clause of the RL class (rl-class-definition) or fact-class declaration.

Format

function assertXPath(String pkg, Object element, String xpath);

See Also

assert, id, object, retract


clearRule

Clears the named rule from the rule session. Removes all of the rule's activations from the agenda.

Format

function clearRule(String name);

See Also

getRuleSession


clearRulesetStack

Empties the ruleset stack.

Format

function clearRulesetStack();

See Also

getRulesetStack, getStrategy, popRuleset, pushRuleset, run, setStrategy


clearWatchRules, clearWatchActivations, clearWatchFacts, clearWatchFocus, clearWatchCompilations, clearWatchAll

The clearWatch functions stop printing debug information.

Format

function clearWatchRules();

function clearWatchActivations();

function clearWatchFacts();

function clearWatchFocus();

function clearWatchCompilations();

function clearWatchAll();

See Also

watchRules, watchActivations, watchFacts, watchFocus, watchCompilations


contains

The contains() function is similar to the contains() method on Java Collection but with includes the ability to handle the presence of JAXBElement in the collection.

Format

contains(Collection c, Object o) returns boolean

Usage

When contains() encounters a JAXBElement in the collection c, it obtains the value class from the JAXBElement and compares it to the Object o.

See Also

assertTree


getCurrentDate

The getCurrentDate function returns the date associated with the CurrentDate fact.

Format

getCurrentDate() returns Calendar

Usage Notes

The effective date and the current date are two orthogonal items. The effective date is used to determine which rules are in affect according to the start and end effective date properties. The CurrentDate fact allows reasoning on a rules engine managed fact representing the "current" date.

Setting the current date does not affect the effective date semantics.

If you want to create rules to reason on the date explicitly in the rules, then use the CurrentDate fact. If you want to assign start and or end effective dates to rules and have the rules in effect determined from a date in the data, then use setEffectiveDate().

See Also

setCurrentDate, getEffectiveDate, setEffectiveDate


getDecisionTrace

Returns the current trace and starts a new trace.

Format

getDecisionTrace() returns DecisionTrace

Usage Notes

See Also

getDecisionTraceLevel, getDecisionTraceLevel, watchRules, watchActivations, watchFacts, watchFocus, watchCompilations


getDecisionTraceLevel

Gets the current decision trace level.

Format

getDecisionTraceLevel() returns int

Usage Notes

Supported decision trace levels include the following levels:

See Also

getDecisionTrace, getDecisionTraceLimit, watchRules, watchActivations, watchFacts, watchFocus, watchCompilations


getDecisionTraceLimit

Returns the current limit on the number of events in a trace.

Format

getDecisionTraceLimit() returns int

Usage Notes

See Also

getDecisionTrace, getDecisionTraceLevel


getEffectiveDate

The getEffectiveDate function returns the current value of the effective date.

Format

getEffectiveDate() returns Calendar

Usage Notes

The effective date and the current date are two orthogonal items. The effective date is used to determine which rules are in affect according to the start and end effective date properties. The CurrentDate fact allows reasoning on a engine managed fact representing the "current" date. Both may be set explicitly.

Setting the current date does not affect the effective date semantics. Setting the effective date does not affect the CurrentDate fact.

If you want to create rules to reason on the date explicitly in the rules, then use the CurrentDate (setCurrentDate()). If you want to assign start and or end effective dates to rules and have the rules in effect determined from a date in the data, then use setEffectiveDate().

See Also

setEffectiveDate, getCurrentDate, setCurrentDate


getFactByType

This function returns an instance of the fact type identified by className if exactly one instance exists in working memory. If no existence exists, null is returned. If more than one instance of the fact type exists in working memory an exception is thrown.

Format

function getFactByType(String className) returns Object

See Also

showFacts


getFactsByType

Returns a list of all facts in working memory that are instances of a specified class.

Format

function getFactsByType(String className) returns List

See Also

showFacts


getRulesetStack

Returns the ruleset stack as an array of ruleset names.

Format

function getRulesetStack() returns String[];

Usage Notes

Returns: the ruleset stack as an array of ruleset names.

Entry 0, the top of the stack, is the focus ruleset. The focus ruleset is the ruleset whose activations are fired first by a subsequent run, runUntilHalt, or step function execution.

See Also

clearRulesetStack, getStrategy, popRuleset, pushRuleset, setRulesetStack, setStrategy


getRuleSession

Returns a Java RuleSession object. An RL Language program could use this RuleSession to dynamically define new classes, rules, functions, or variables.

Format

function getRuleSession() returns RuleSession;

Example

rule learn {
  if (fact f1 && …)
  {
    RuleSession rs = getRuleSession();
    rs.executeRuleset("rule newRule { if fact f1 && fact f2 && … { … } }");
  }
}

See Also

clearRule


getStrategy

Returns the current strategy. Table 2-7 shows the possible strategy values.

Format

function getStrategy() returns String;

See Also

clearRulesetStack, getRulesetStack, popRuleset, pushRuleset, setStrategy


halt

The halt function halts execution of the currently firing rule, and returns control to the run, runUntilHalt, or step function that caused the halted rule to run. The agenda is left intact, so that a subsequent run, runUntilHalt, or step can be executed to resume rule firings.

The halt function has no effect if it is invoked outside the context of a run, runUntilHalt, or step function.

Format

function halt();

See Also

reset, run, runUntilHalt, step


id

Return the fact id associated with the object obj. If obj is not associated with a fact, returns -1.

Format

function id(Object obj) returns int;

See Also

assert, object, retract


isErrorInRuleConditionSuppressed

Error suppression happens at each test in the rule condition. Each test is evaluated separately and if an error happens during the evaluation and error suppression is enabled, the error is suppressed. When an error occurs during the evaluation of a test, it means that the result of the test is unknown. Internally, the rule engine uses three-valued logic to represent this state (true/false/unknown, see http://en.wikipedia.org/wiki/Three-valued_logic). When a true/false value is required, a value of unknown is mapped to false.

Errors in a test can either be in the RL domain (detected by the engine) or in the Java domain (thrown by a Java method invoked in the test). In the RL domain, RLNullPointerException, an attempt to de-reference a null object reference in an RL expression, is the most common error. RLArithmeticException (integer divide by 0) and RLIllegalArgumentException are infrequent. RLArrayIndexOutOfBoundsException, RLClassCastException, and RLCloneNotSupportedException are rare.

Java domain exceptions are those thrown by a Java method invoked from the rule condition. Those exceptions are wrapped in an RL exception, JavaException with the exception thrown by the method available via getCause(). When an exception is thrown by a Java method the engine can not make any further distinction. For example, it is possible that a null value passed to the method caused the method to throw an exception but the rule engine has no way to know whether or not the null was the cause.

Error suppression can be controlled by invoking a built-in function. A common place to invoke it is in the initial actions of a decision function.

Format

isErrorInRuleConditionSuppressed() returns boolean

Usage Notes

The RL signature is: isErrorInRuleConditionSuppressed() returns boolean.

See Also

setErrorInRuleConditionSuppressed


object

Return the object associated with the given fact id. If there is no such fact id, returns null.

Format

function object(int factId) returns Object;

See Also

assert, id, retract


println

Print the given value to the RuleSession output writer.

Format

function println(char c);

function println(char[] ca);

function println(int i);

function println(long l);

function println(float f);

function println(double d);

function println(boolean b);

function println(Object obj);


popRuleset

If the stack is empty, popRuleset throws RLRuntimeException. If the stack is not empty, popRuleset pops the focus off the stack and returns it.

All entries are shifted down one position, and the new focus is the new top of stack, entry 0.

Entry 0, the top of the stack, is the focus ruleset. The focus ruleset is the ruleset whose activations are fired first by a subsequent run, runUntilHalt, or step function execution.

Format

function popRuleset() returns String;

Example 2-50 Using popRuleset and Throwing RLRuntimeException

clearRulesetStack();
popRuleset();        // RLRuntimeException

See Also

clearRulesetStack, getRulesetStack, getStrategy, pushRuleset, setStrategy


pushRuleset

Push the given ruleset onto the stack and make it the focus. It is an error to push a ruleset that is already the focus (RLIllegalArgumentException is thrown for this error).

Entry 0, the top of the stack, is the focus ruleset. The focus ruleset is the ruleset whose activations are fired first by a subsequent run, runUntilHalt, or step function execution.

Format

function pushRuleset(String focus);

Examples

Example 2-51 shows the RL Language using the pushRuleset function. Example 2-52 shows the RL Language using the popRuleset function.

Example 2-51 Using pushRuleset - Throws RLIllegalArgumentException

clearRulesetStack();
pushRuleset("main");        // focus is "main"
pushRuleset("main");        // RLIllegalArgumentException

Example 2-52 Using popRuleset - Throws RLRuntimeException

clearRulesetStack();
popRuleset();        // RLRuntimeException

See Also

clearRulesetStack, getRulesetStack, getStrategy, popRuleset, setStrategy


retract

Remove the fact associated with the object obj from working memory.

Format

function retract(Object obj);

Usage Notes

Retract may affect the agenda. Activations that depend on the retracted fact are removed from the agenda.

Note, rules that have conditions that test for non-existence of facts (using !) may place new activations on the agenda.

See Also

assert, id, object


reset

Clears all facts from working memory, clears all activations from the agenda, and reevaluates non-final global variable initialization expressions.

Format

function reset();

See Also

halt, run, runUntilHalt, step


run

Fire rule activations on the agenda until:

Format

function run() returns int;

function run(String rulesetName) returns int;

Usage Notes

If the argument, rulesetName is supplied, the named ruleset is pushed on the top of the ruleset stack before firing any rules.

If a null rulesetName is supplied, the ruleset stack is not modified before firing rules.

If no rulesetName is supplied and the default main ruleset is not on the ruleset stack, then the main ruleset is placed at the bottom of the ruleset stack before firing any rules.

Returns: int, the number of rules fired.

See Also

halt, reset, runUntilHalt, step


runUntilHalt

This function fires rule activations until halt is called. Unlike run and step, runUntilHalt does not return when the agenda is empty. Also, runUntilHalt does not pop the bottommost ruleset name from the ruleset stack. Instead, it waits for the agenda to contain activations.

Format

function runUntilHalt() returns int;

Usage Notes

The only way for activations to be added to the agenda while the main RuleSession thread is busy executing runUntilHalt is for a second thread to either:

  1. Modify Java bean facts with PropertyChangeListeners.

  2. Execute assert or retract functions.

Rules must be designed carefully when using runUntilHalt. For example, a rule that attempts to find a fact with the minimum value of a property will fire when the first instance of the fact is asserted, and then every time another instance is asserted with a lower valued property.

See Also

halt, reset, run, step


setCurrentDate

The setCurrentDate function sets the date for reasoning on an engine managed fact representing the "current" date (with the CurrentDate fact).

Format

setCurrentDate(Calendar newDate)

Usage Notes

The RLIllegalArgumentException exception is thrown if the newDate argument is null.

If you need to reason on the date explicitly in the rules, then use the CurrentDate fact. If you want to assign start and end effective dates to rules and have the rules in effect determined from a date in the data, then they should use setEffectiveDate. The setEffectiveDate function does not affect the CurrentDate fact.

By default the value of the current date is managed implicitly by the rules engine. The value of the CurrentDate fact is updated to the current system date and (re)asserted internally when a run family of built-in functions is invoked. This is done before any rules fire so that the new current date is evaluated in rule conditions. In the case of runUntilHalt, this update occurs each time there is a transition from 0 rules on the agenda to > 0 rules on the agenda.

After the user invokes the setCurrentDate function, it becomes the responsibility of the user to update the current date as required. The rules engine no longer manages it implicitly. This remains in effect until the reset function is invoked. After the current date is set explicitly with setCurrentDate, any invocation of setCurrentDate function that would result in time going backward, set to an earlier point in time, is an error and an RLIllegalArgumentException is thrown. After the reset function is invoked, the current date may be set to any value.

See Also

getCurrentDate, getEffectiveDate, setEffectiveDate


setDecisionTraceLevel

Sets the decision trace level to the specified level.

Format

setDecisionTraceLevel(int level)

Usage Notes

Supported decision trace levels include the following levels:

See Also

getDecisionTrace, getDecisionTraceLevel, getDecisionTraceLevel, setDecisionTraceLimit, watchRules, watchActivations, watchFacts, watchFocus, watchCompilations


setDecisionTraceLimit

Sets the limit on the number of events in a trace.

Format

setDecisionTraceLimit(int count)

Usage Notes

The default value is 10000.

See Also

getDecisionTrace, getDecisionTraceLevel, getDecisionTraceLevel, setDecisionTraceLevel


setEffectiveDate

The setEffectiveDate function updates the effective date in the rules engine.

By default, the value of the effective date is managed implicitly by the rules engine. In this case, when a run family of built-in functions is invoked the effective date is updated to the current system date. This is done before any rules fire so that the new effective date is applied before rules begin to fire. In the case of runUntilHalt, this update occurs each time there is a transition from 0 rule activations on the agenda to > 0 rule activations on the agenda.

Format

setEffectiveDate(Calendar newDate)

Usage Notes

Invoking setEffectiveDate is the only way that you can alter the effective date. After the reset function is invoked, the effective date may be set to any value.

The RLIllegalArgumentException exception is thrown if the newDate argument is null.

After you invoke the setEffectiveDate function, it becomes the responsibility of the application to update the effective date as required. The rules engine no longer manages it implicitly.

This remains in effect until the reset function is invoked.

This is useful for debugging, performing rule evaluation at a "point in time", or other use cases that require application control of the effective date.

See Also

getEffectiveDate, getCurrentDate, setCurrentDate


setErrorInRuleConditionSuppressed

Error suppression happens at each test in the rule condition. Each test is evaluated separately and if an error happens during the evaluation and error suppression is enabled, the error is suppressed. When an error occurs during the evaluation of a test, it means that the result of the test is unknown. Internally, the rule engine uses three-valued logic to represent this state (true/false/unknown, see http://en.wikipedia.org/wiki/Three-valued_logic). When a true/false value is required, a value of unknown is mapped to false.

Errors in a test can either be in the RL domain (detected by the engine) or in the Java domain (thrown by a Java method invoked in the test). In the RL domain, RLNullPointerException, an attempt to de-reference a null object reference in an RL expression, is the most common error. RLArithmeticException (integer divide by 0) and RLIllegalArgumentException are infrequent. RLArrayIndexOutOfBoundsException, RLClassCastException, and RLCloneNotSupportedException are rare.

Java domain exceptions are those thrown by a Java method invoked from the rule condition. Those exceptions are wrapped in an RL exception, JavaException with the exception thrown by the method available via getCause(). When an exception is thrown by a Java method the engine can not make any further distinction. For example, it is possible that a null value passed to the method caused the method to throw an exception but the rule engine has no way to know whether or not the null was the cause.

Error suppression can be controlled by invoking a built-in function. A common place to invoke it is in the initial actions of a decision function.

Format

setErrorInRuleConditionSuppressed(boolean bv) returns boolean

Usage Notes

The RL signature is: setErrorInRuleConditionSuppressed(boolean bv) returns boolean.

Passing a value of true will enable error suppression. The return value is the previous setting.

The current setting can be queried with the isErrorInRuleConditionSuppressed built-in function.

See Also

isErrorInRuleConditionSuppressed


setRulesetStack

Sets the ruleset stack to the given array of ruleset names.

Entry 0, the top of the stack, is the focus ruleset, which is the ruleset whose activations will be fired first by a subsequent run, runUntilHalt, or step function execution.

Format

function setRulesetStack(String[] rulesetStack

See Also

clearRulesetStack, getRulesetStack, getStrategy, popRuleset, pushRuleset, setStrategy


setStrategy

Strategy specifies the order in which activations from the same ruleset and with the same priority are executed. Table 2-7 shows the valid strategy values.

Table 2-7 Strategy Values for setStrategy and getStrategy Functions

Strategy Description

queue

Activations are fired in order from oldest to newest.

stack

Activations are fired in order from newest to oldest.


Format

function setStrategy(String strategy);

See Also

clearRulesetStack, getRulesetStack, getStrategy, popRuleset, pushRuleset


showActivations

The show functions print rule session state to the output Writer. State that can be shown is: Activations all activations on the agenda

Format

function showActivations();

See Also

clearWatchRules, clearWatchActivations, clearWatchFacts, clearWatchFocus, clearWatchCompilations, clearWatchAll, showFacts, watchRules, watchActivations, watchFacts, watchFocus, watchCompilations


showFacts

The show functions print rule session state to the output Writer. State that can be shown is: all facts in working memory.

Format

function showFacts();

See Also

clearWatchRules, clearWatchActivations, clearWatchFacts, clearWatchFocus, clearWatchCompilations, clearWatchAll, showActivations, watchRules, watchActivations, watchFacts, watchFocus, watchCompilations


step

Fire rule activations on the agenda until:

Format

function step(int numRulesToFire) returns int;

function step(int numRulesToFire, String rulesetName) returns int;

function step(int numRulesToFire, boolean errorIfLimitHit) returns int;

function step(int numRulesToFire, String rulesetName, boolean errorIfLimitHit) returns int;

Usage Notes

If no ruleset name is supplied and the main ruleset is not on the ruleset stack, then the main ruleset is placed at the bottom of the ruleset stack before firing any rules.

If a ruleset named, rulesetName, is supplied, the specified ruleset is pushed on the top of the ruleset stack before firing any rules. If a null ruleset name is supplied, the ruleset stack is not modified before firing rules.

Returns the integer number of rules fired.

The last two signatures allow the caller to specify whether hitting the firing limit (numRulesToFire) should be treated as an error condition or not. The default is false, it is not an error condition to hit the limit.

Invoking the step function with a value of true for the errorIfLimitHit argument can be used to catch infinite rule firing loops that can occur due to a bug in the rules as written.

See Also

halt, reset, run, runUntilHalt


watchRules, watchActivations, watchFacts, watchFocus, watchCompilations

The watch functions turn on printing of information about important rule session events. The information is printed to the output Writer whenever the events occur. Use a clearWatch function to turn off printing.

Table 2-8 describes the available debugging information.

Table 2-8 Watch Functions Event Descriptions

Debug Watch Rule Session Event Description

watch

Rule session event description

Rules

Information about rule firings (execution of activations)

Activations

Addition or removal of activations from the agenda

Facts

Assertion, retraction, or modification of facts in working memory

Focus

Pushing or popping of the ruleset stack. The top of the ruleset stack is called the focus ruleset, and all activations on the agenda from the focus ruleset will be fired before the focus is popped and the next ruleset on the stack becomes the focus.

Compilations

When a rule's conditions are added to the rete network, information about how the condition parts are shared with existing rules is printed. "=" indicates sharing. The order that rules are defined can affect sharing and thus can affect performance.

All

Includes information shown with watch Rules, watch Activations, watch Facts, watch Compilations and watch Focus.


Format

function watchRules();

function watchActivations();

function watchFacts();

function watchFocus();

function watchCompilations();

function watchAll();

See Also

clearWatchRules, clearWatchActivations, clearWatchFacts, clearWatchFocus, clearWatchCompilations, clearWatchAll, showActivations, showFacts