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Oracle® Database PL/SQL Packages and Types Reference
11g Release 2 (11.2)

Part Number E16760-04
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125 DBMS_RULE

The DBMS_RULE package contains subprograms that enable the evaluation of a rule set for a specified event.

This chapter contains the following topics:


Using DBMS_RULE

This section contains topics which relate to using the DBMS_RULE package.


Overview

This package contains subprograms that enable the evaluation of a rule set for a specified event.

See Also:


Security Model

PUBLIC is granted EXECUTE privilege on this package.

See Also:

Oracle Database Security Guide for more information about user group PUBLIC

Summary of DBMS_RULE Subprograms

Table 125-1 DBMS_RULE Package Subprograms

Subprogram Description

CLOSE_ITERATOR Procedure

Closes an open iterator

EVALUATE Procedures

Evaluates the rules in the specified rule set that use the evaluation context specified

GET_NEXT_HIT Function

Returns the next rule that evaluated to TRUE from a true rules iterator, or returns the next rule that evaluated to MAYBE from a maybe rules iterator; returns NULL if there are no more rules that evaluated to TRUE or MAYBE.



CLOSE_ITERATOR Procedure

This procedure closes an open iterator.

Syntax

DBMS_RULE.CLOSE_ITERATOR(
  iterator  IN  BINARY_INTEGER);

Parameter

Table 125-2 CLOSE_ITERATOR Procedure Parameter

Parameter Description

iterator

The iterator to be closed


Usage Notes

This procedure requires an open iterator that was returned by an earlier call to DBMS_RULE.EVALUATE in the same session. The user who runs this procedure does not require any privileges on the rule set being evaluated.

Closing an iterator frees resources, such as memory, associated with the iterator. Therefore, Oracle recommends that you close an iterator when it is no longer needed.


EVALUATE Procedures

This procedure evaluates the rules in the specified rule set that use the evaluation context specified for a specified event.

This procedure is overloaded. The true_rules and maybe_rules parameters are mutually exclusive with the true_rules_iterator and maybe_rules_iterator parameters. In addition, the procedure with the true_rules and maybe_rules parameters includes the stop_on_first_hit parameter, but the other procedure does not.

Syntax

DBMS_RULE.EVALUATE(
  rule_set_name        IN   VARCHAR2,
  evaluation_context   IN   VARCHAR2,
  event_context        IN   SYS.RE$NV_LIST               DEFAULT NULL,
  table_values         IN   SYS.RE$TABLE_VALUE_LIST      DEFAULT NULL,
  column_values        IN   SYS.RE$COLUMN_VALUE_LIST     DEFAULT NULL,
  variable_values      IN   SYS.RE$VARIABLE_VALUE_LIST   DEFAULT NULL,
  attribute_values     IN   SYS.RE$ATTRIBUTE_VALUE_LIST  DEFAULT NULL,
  stop_on_first_hit    IN   BOOLEAN                      DEFAULT FALSE,
  simple_rules_only    IN   BOOLEAN                      DEFAULT FALSE,
  true_rules           OUT  SYS.RE$RULE_HIT_LIST,
  maybe_rules          OUT  SYS.RE$RULE_HIT_LIST);

DBMS_RULE.EVALUATE(
  rule_set_name         IN   VARCHAR2,
  evaluation_context    IN   VARCHAR2,
  event_context         IN   SYS.RE$NV_LIST               DEFAULT NULL,
  table_values          IN   SYS.RE$TABLE_VALUE_LIST      DEFAULT NULL,
  column_values         IN   SYS.RE$COLUMN_VALUE_LIST     DEFAULT NULL,
  variable_values       IN   SYS.RE$VARIABLE_VALUE_LIST   DEFAULT NULL,
  attribute_values      IN   SYS.RE$ATTRIBUTE_VALUE_LIST  DEFAULT NULL,
  simple_rules_only     IN   BOOLEAN                      DEFAULT FALSE,
  true_rules_iterator   OUT  BINARY_INTEGER,
  maybe_rules_iterator  OUT  BINARY_INTEGER);

Parameters

Table 125-3 EVALUATE Procedure Parameters

Parameter Description

rule_set_name

Name of the rule set in the form [schema_name.]rule_set_name. For example, to evaluate all of the rules in a rule set named hr_rules in the hr schema, enter hr.hr_rules for this parameter. If the schema is not specified, then the schema of the current user is used.

evaluation_context

An evaluation context name in the form [schema_name.]evaluation_context_name. If the schema is not specified, then the name of the current user is used.

Only rules that use the specified evaluation context are evaluated.

event_context

A list of name-value pairs that identify events that cause evaluation

table_values

Contains the data for table rows using the table aliases specified when the evaluation context was created. Each table alias in the list must be unique.

column_values

Contains the partial data for table rows. It must not contain column values for tables, whose values are already specified in table_values.

variable_values

A list containing the data for variables.

The only way for an explicit variable value to be known is to specify its value in this list.

If an implicit variable value is not specified in the list, then the function used to obtain the value of the implicit variable is invoked. If an implicit variable value is specified in the list, then this value is used and the function is not invoked.

attribute_values

Contains the partial data for variables. It must not contain attribute values for variables whose values are already specified in variable_values.

stop_on_first_hit

If TRUE, then the rules engine stops evaluation as soon as it finds a TRUE rule.

If TRUE and there are no TRUE rules, then the rules engine stops evaluation as soon as it finds a rule that may evaluate to TRUE given more data.

If FALSE, then the rules engine continues to evaluate rules even after it finds a TRUE rule.

simple_rules_only

If TRUE, then only those rules that are simple enough to be evaluated fast (without issuing SQL) are considered for evaluation.

If FALSE, then evaluates all rules.

true_rules

Receives the output of the EVALUATE procedure into a varray of RE$RULE_HIT_LIST type.

If no rules evaluate to TRUE, then true_rules is empty.

If at least one rule evaluates to TRUE and stop_on_first_hit is TRUE, then true_rules contains one rule that evaluates to TRUE.

If stop_on_first_hit is FALSE, then true_rules contains all rules that evaluate to TRUE.

maybe_rules

If all rules can be evaluated completely, without requiring any additional data, then maybe_rules is empty.

If stop_on_first_hit is TRUE, then if there is at least one rule that may evaluate to TRUE given more data, and no rules evaluate to TRUE, then maybe_rules contains one rule that may evaluate to TRUE.

If stop_on_first_hit is FALSE, then maybe_rules contains all rules that may evaluate to TRUE given more data.

true_rules_iterator

Contains the iterator for accessing rules that are TRUE

maybe_rules_iterator

Contains the iterator for accessing rules that may be TRUE given additional data or the ability to issue SQL


Usage Notes

Note:

Rules in the rule set that use an evaluation context different from the one specified are not considered for evaluation.

The rules in the rule set are evaluated using the data specified for table_values, column_values, variable_values, and attribute_values. These values must refer to tables and variables in the specified evaluation context. Otherwise, an error is raised.

The caller may specify, using stop_on_first_hit, if evaluation must stop as soon as the first TRUE rule or the first MAYBE rule (if there are no TRUE rules) is found.

The caller may also specify, using simple_rules_only, if only rules that are simple enough to be evaluated fast (which means without SQL) should be considered for evaluation. This makes evaluation faster, but causes rules that cannot be evaluated without SQL to be returned as MAYBE rules.

Partial evaluation is supported. The EVALUATE procedure can be called with data for only some of the tables, columns, variables, or attributes. In such a case, rules that cannot be evaluated because of a lack of data are returned as MAYBE rules, unless they can be determined to be TRUE or FALSE based on the values of one or more simple expressions within the rule. For example, given a value of 1 for attribute "a.b" of variable "x", a rule with the following rule condition can be returned as TRUE, without a value for table "tab":

(:x.a.b = 1) or (tab.c > 10)

The results of an evaluation are the following:

The caller may specify whether the procedure returns all of the rules that evaluate to TRUE and MAYBE for the event or an iterator for rules that evaluate to TRUE and MAYBE. A true rules iterator enables the client to fetch each rule that evaluates to TRUE one at a time, and a maybe rules iterator enables the client to fetch each rule that evaluates to MAYBE one at a time.

If you use an iterator, then you use the GET_NEXT_HIT function in the DBMS_RULE package to retrieve the next rule that evaluates to TRUE or MAYBE from an iterator. Oracle recommends that you close an iterator if it is no longer needed to free resources, such as memory, used by the iterator. An iterator can be closed in the following ways:

To run the DBMS_RULE.EVALUATE procedure, a user must meet at least one of the following requirements:


GET_NEXT_HIT Function

This function returns the next rule that evaluated to TRUE from a true rules iterator, or returns the next rule that evaluated to MAYBE from a maybe rules iterator. The function returns NULL if there are no more rules that evaluated to TRUE or MAYBE.

Syntax

DBMS_RULE.GET_NEXT_HIT(
  iterator  IN  BINARY_INTEGER)
RETURN SYS.RE$RULE_HIT;

Parameter

Table 125-4 GET_NEXT_HIT Function Parameter

Parameter Description

iterator

The iterator from which the rule that evaluated to TRUE or MAYBE is retrieved


Usage Notes

This procedure requires an open iterator that was returned by an earlier call to DBMS_RULE.EVALUATE in the same session. The user who runs this procedure does not require any privileges on the rule set being evaluated.

When an iterator returns NULL, it is closed automatically. If an open iterator is no longer needed, then use the CLOSE_ITERATOR procedure in the DBMS_RULE package to close it.

Note:

This function raises an error if the rule set being evaluated was modified after the call to the DBMS_RULE.EVALUATE procedure that returned the iterator. Modifications to a rule set include added rules to the rule set, changing existing rules in the rule set, dropping rules from the rule set, and dropping the rule set.

See Also: