|Oracle® Database Application Developer's Guide - Expression Filter
10g Release 1 (10.1)
Part Number B10821-01
Oracle Expression Filter is a feature of Oracle Database that allows application developers to store, index, and evaluate conditional expressions (expressions) in one or more columns of a relational table. Expressions are a useful way to describe interests in expected data. Expression Filter matches incoming data with expressions stored in a column to identify rows of interest. It can also derive complex relationships by matching data in one table with expressions in a second table. Expression Filter simplifies SQL queries; allows expressions to be inserted, updated, and deleted without changing the application; and enables reuse of conditional expressions in business rules by separating them from the application and storing them in the database. Applications involving information distribution, demand analysis, and task assignment can benefit from Expression Filter.
Expression Filter provides a datatype, operator, and indextype to store, evaluate, and index expressions that describe an interest in a data item or piece of information. Expressions are stored in a column of a user table. Expression Filter matches expressions in a column with a data item passed by a SQL statement or with data stored in one or more tables, and evaluates each expression to be true or false. Optionally, expressions can be indexed when using the Enterprise Edition of Oracle Database. Expression Filter includes the following elements:
Expression datatype: A virtual datatype created through a constraint placed on a VARCHAR2 column in a user table that stores expressions.
EVALUATE operator: An operator that evaluates expressions for each data item.
Administrative utilities: A set of utilities that validate expressions and suggest optimal index structure.
Expression indexing: Enhances performance of the
EVALUATE operator for large expression sets. Expression indexing is available in Oracle Database Enterprise Edition.
The following sections are examples of how you can use Expression Filter.
Expression Filter can match incoming data with conditional expressions stored in the database to identify rows of interest. For example, consider an application that matches buyers and sellers of cars. A table called
Consumer includes a column called
BUYER_PREFERENCES with an Expression datatype. The
BUYER_PREFERENCES column stores an expression for each consumer that describes the kind of car the consumer wants to purchase, including make, model, year, mileage, color, options, and price. Data about cars for sale is included with the
EVALUATE operator in the SQL
WHERE clause. The SQL
EVALUATE operator matches the incoming car data with the expressions to find prospective buyers.
EVALUATE operator also enables batch processing of incoming data. Data can be stored in a table called
CARS and matched with expressions stored in the
CONSUMER table using a join between the two tables.
EVALUATE operator saves time by matching a set of expressions with incoming data and enabling large expression sets to be indexed for performance. This saves labor by allowing expressions to be inserted, updated, and deleted without changing the application and providing a results set that can be manipulated in the same SQL statement, for instance to order or group results. In contrast, a procedural approach stores results in a temporary table that must be queried for further processing, and those expressions cannot be indexed.
Expression Filter can convey N-to-M (many-to-many) relationships between tables. Using the previous example:
A car may be of interest to one or more buyers.
A buyer may be interested in one or more cars.
A seller may be interested in one or more buyers.
To answer questions about these relationships, the incoming data about cars is stored in a table called
CARS with an Expression column (column of Expression datatype) called
CONSUMERS table includes a column called
BUYER_PREFERENCES. The SQL
EVALUATE operator can answer questions such as:
What cars are of interest to each consumer?
What buyers are of interest to each seller?
What demand exists for each car? This can help to determine optimal pricing.
What unsatisfied demand is there? This can help to determine inventory requirements.
This declarative approach saves labor. No action is needed if changes are made to the data or the expressions. Compare this to the traditional approach where a mapping table is created to store the relationship between the two tables. A trigger must be defined to recompute the relationships and to update the mapping table if the data or expressions change. In this case, new data must be compared to all expressions, and a new expression must be compared to all data.
Expression Filter is a good fit for applications where the data has the following attributes:
A large number of data items exists to be evaluated.
Each data item has structured data attributes, for example
VARCHAR, NUMBER, DATE, XMLTYPE.
Incoming data is evaluated by a significant number of unique and persistent queries containing expressions.
The expression (in SQL
WHERE clause format) describes an interest in incoming data items.
The expressions compare attributes to values using relational operators (=, !=, <, >, and so on).
Expressions describe interests in an item of data. Expressions are stored in a column of a user table and compared, using the SQL
EVALUATE operator, to incoming data items specified in a SQL
WHERE clause or to a table of data. Expressions are evaluated as true or false or return a null value if an expression does not exist for a row.
An expression describes interest in an item of data using one or more variables, known as elementary attributes. An expression can also include literals, Oracle supplied functions, user-defined functions, and table aliases. A valid expression consists of one or more simple conditions called predicates. The predicates in the expression are linked by the logical operators
OR. Expressions must adhere to the SQL
WHERE clause format. (For more information about the SQL
WHERE clause, see Oracle Database SQL Reference.) An expression is not required to use all the defined elementary attributes; however, the incoming data must provide a value for every elementary attribute. Null is an acceptable value.
For example, the following expression includes the
UPPER Oracle supplied function and captures the interest of a user in a car (the data item) with the model, price, and year as elementary attributes.
UPPER(Model) = 'TAURUS' and Price < 20000 and Year > 2000
Expressions are stored in a column of a user table with an Expression datatype. The values stored in a column of this type are constrained to be expressions. (See Section 1.2.2.) A user table can have one or more Expression columns. A query to display the contents of an Expression column displays the expressions in string format.
You insert, update, and delete expressions using standard SQL. A group of expressions that are stored in a single column is called an expression set and shares a common set of elementary attributes. This set of elementary attributes plus any functions used in the expressions are the metadata for the expression set. This metadata is referred to as the attribute set. The attribute set consists of the elementary attribute names and their datatypes and any functions used in the expressions. The attribute set is used by the Expression column to validate changes and additions to the expression set. An expression stored in the Expression column can use only the elementary attribute and functions defined in the corresponding attribute set. Expressions cannot contain subqueries.
Define an attribute set. See Section 1.2.1.
Define an Expression column in a user table. See Section 1.2.2.
Insert expressions in the table. See Section 1.2.3.
Apply the SQL
EVALUATE operator to compare expressions to incoming data items. See Section 1.3.
The remaining sections in this chapter guide you through this procedure.
A special form of an Oracle object type is used to create an attribute set. (For more information about object types, see Oracle Database Application Developer's Guide - Object-Relational Features.)
The attribute set defines the elementary attributes for an expression set. It implicitly allows all Oracle supplied SQL functions to be valid references in the expression set. If the expression set refers to a user-defined function, it must be explicitly added to the attribute set. An elementary attribute in an attribute set can refer to data stored in another database table using table alias constructs. One or more or all elementary attributes in an attribute set can be table aliases. If an elementary attribute is a table alias, the value assigned to the elementary attribute is a
ROWID from the corresponding table. For more information about table aliases, see Appendix A.
Use an existing object type to create an attribute set with the same name as the object type. This approach is most appropriate to use when the attribute set does not contain any table alias elementary attributes. You use the CREATE_ATTRIBUTE_SET procedure of the DBMS_EXPFIL package. See Example 1-1.
Individually add elementary attributes to an existing attribute set. Expression Filter automatically creates an object type to encapsulate the elementary attributes and gives it the same name as the attribute set. This approach is most appropriate to use when the attribute set contains one or more elementary attributes defined as table aliases. You use the ADD_ELEMENTARY_ATTRIBUTE procedure of the DBMS_EXPFIL package. See Example 1-2.
If the expressions refer to user-defined functions, you must add the functions to the corresponding attribute set, using the ADD_FINCTIONS procedure of the DBMS_EXPFIL package. See Example 1-3.
Example 1-1 shows how to use an existing object type to create an attribute set. It uses the CREATE_ATTRIBUTE_SET procedure.
Example 1-1 Defining an Attribute Set From an Existing Object Type
CREATE OR REPLACE TYPE Car4Sale AS OBJECT (Model VARCHAR2(20), Year NUMBER, Price NUMBER, Mileage NUMBER); / BEGIN DBMS_EXPFIL.CREATE_ATTRIBUTE_SET(attr_set => 'Car4Sale', from_type => 'YES'); END; /
Example 1-2 shows how to create an attribute set
Car4Sale and how to define the variables one at a time. It uses the CREATE_ATTRIBUTE_SET and ADD_ELEMENTARY_ATTRIBUTE procedures.
Example 1-2 Defining an Attribute Set Incrementally
BEGIN DBMS_EXPFIL.CREATE_ATTRIBUTE_SET(attr_set => 'Car4Sale'); DBMS_EXPFIL.ADD_ELEMENTARY_ATTRIBUTE( attr_set => 'Car4Sale', attr_name => 'Model', attr_type => 'VARCHAR2(20)'); DBMS_EXPFIL.ADD_ELEMENTARY_ATTRIBUTE( attr_set => 'Car4Sale', attr_name => 'Year', attr_type => 'NUMBER'); DBMS_EXPFIL.ADD_ELEMENTARY_ATTRIBUTE( attr_set => 'Car4Sale', attr_name => 'Price', attr_type => 'NUMBER'); DBMS_EXPFIL.ADD_ELEMENTARY_ATTRIBUTE( attr_set => 'Car4Sale', attr_name => 'Mileage', attr_type => 'NUMBER'); END;/
If the expressions refer to user-defined functions, you must add the functions to the corresponding attribute set. Example 1-3 shows how to add user-defined functions, using the ADD_FUNCTIONS procedure, to an attribute set.
Example 1-3 Adding User-Defined Functions to an Attribute Set
CREATE or REPLACE FUNCTION HorsePower(Model VARCHAR2, Year VARCHAR2) return NUMBER isBEGIN -- Derive HorsePower from other relational tables uisng Model and Year values.-- return 200; END HorsePower; / CREATE or REPLACE FUNCTION CrashTestRating(Model VARCHAR2, Year VARCHAR2) return NUMBER is BEGIN -- Derive CrashTestRating from other relational tables using Model -- -- and Year values. -- return 5; END CrashTestRating; / BEGIN DBMS_EXPFIL.ADD_FUNCTIONS (attr_set => 'Car4Sale', funcs_name => 'HorsePower'); DBMS_EXPFIL.ADD_FUNCTIONS (attr_set => 'Car4Sale', funcs_name => 'CrashTestRating'); END; /
Expression is a virtual datatype. Assigning an attribute set to a
VARCHAR2 column in a user table creates an Expression column. The attribute set determines which elementary attributes and user-defined functions can be used in the expression set. An attribute set can be used to create multiple columns of Expression datatype in the same table and in other tables in the same schema. Note that an attribute set in one schema cannot be associated with a column in another schema.
VARCHAR2 column to a table or create a table with the
VARCHAR2 column. An existing
VARCHAR2 column in a user table can also be used for this purpose. The following example creates a table with a
Interest, that will be used with an attribute set:
CREATE TABLE Consumer (CId NUMBER, Zipcode NUMBER, Phone VARCHAR2(12), Interest VARCHAR2(200));
BEGIN DBMS_EXPFIL.ASSIGN_ATTRIBUTE_SET ( attr_set => 'Car4Sale', expr_tab => 'Consumer', expr_col => 'Interest'); END; /
Figure 1-1 is a conceptual image of consumers' interests (in trading cars) being captured in a
Figure 1-1 Expression Datatype
You use standard SQL to insert, update, and delete expressions. When an expression is inserted or updated, it is checked for correct syntax and constrained to use the elementary attributes and functions specified in the corresponding attribute set. An error message is returned if the expression is not correct. For more information about evaluation semantics, see Section 1.4.
Example 1-4 Inserting an Expression into the Consumer Table
INSERT INTO Consumer VALUES (1, 32611, '917 768 4633', 'Model=''Taurus'' and Price < 15000 and Mileage < 25000'); INSERT INTO Consumer VALUES (2, 03060, '603 983 3464', 'Model=''Mustang'' and Year > 1999 and Price < 20000');
If an expression refers to a user-defined function, the function must be added to the corresponding attribute set (as shown in Example 1-3). Example 1-5 shows how to insert an expression with a reference to a user-defined function,
HorsePower, into the
Example 1-5 Inserting an Expression That References a User-Defined Function
INSERT INTO Consumer VALUES (3, 03060, '603 484 7013', 'HorsePower(Model, Year) > 200 and Price < 20000');
Expression data can be loaded into an Expression column using SQL*Loader. For more information about bulk loading, see Section 5.1.
You use the SQL
EVALUATE operator in the
WHERE clause of a SQL statement to compare stored expressions to incoming data items. The SQL
EVALUATE operator returns
1 for an expression that matches the data item and
0 for an expression that does not match. For any null values stored in the Expression column, the SQL
EVALUATE operator returns
EVALUATE operator has two arguments: the name of the column storing the expressions and the data item to which the expressions are compared. In the data item argument, values must be provided for all elementary attributes in the attribute set associated with the Expression column. Null is an acceptable value. The data item can be specified either as string-formatted name-value pairs or as an
In the following example, the query returns a row from the
Consumer table if the expression in the
Interest column evaluates to true for the data item:
SELECT * FROM Consumer WHERE EVALUATE (Consumer.Interest, <data item>) = 1;
If the values of all the elementary attributes in the attribute set can be represented as readable values, such as those stored in
NUMBER datatypes and the constructors formatted as a string, then the data item can be formatted as a string:
EVALUATE (VARCHAR2, VARCHAR2) returns NUMBER;
SELECT * FROM Consumer WHERE EVALUATE (Consumer.Interest, 'Model=>''Mustang'', Year=>2000, Price=>18000, Mileage=>22000' ) = 1;
If a data item does not require a constructor for any of its elementary attribute values, then a list of values provided for the data item can be formatted as a string (name-value pairs) using two
getVarchar methods (a
STATIC method and a
MEMBER method) in the object type associated with the attribute set. The
STATIC method formats the data item without creating the object instance. The
MEMBER method can be used if the object instance is already available.
MEMBER methods are implicitly created for the object type and can be used as shown in the following example:
SELECT * FROM Consumer WHERE EVALUATE (Consumer.Interest, Car4Sale.getVarchar('Mustang', -- STATIC getVarchar API -- 2000, 18000, 22000) ) = 1; SELECT * FROM Consumer WHERE EVALUATE (Consumer.Interest, Car4Sale('Mustang', 2000, 18000, 22000).getVarchar() -- MEMBER getVarchar() API -- ) = 1;
Any data item can be formatted using an AnyData instance. AnyData is an Oracle supplied object type that can hold instances of any Oracle datatype, both Oracle supplied and user-defined. For more information, see Oracle Database Application Developer's Guide - Object-Relational Features.
EVALUATE (VARCHAR2, AnyData) returns NUMBER;
An instance of the object type capturing the corresponding attribute set is converted into an AnyData instance using the AnyData's
convertObject method. Using the previous example, the data item can be passed to the SQL
EVALUATE operator by converting the instance of the
Car4Sale object type into AnyData, as shown in the following example:
SELECT * FROM Consumer WHERE EVALUATE (Consumer.Interest, AnyData.convertObject( Car4Sale('Mustang', 2000, 18000, 22000)) ) = 1;
A data item formatted as an AnyData instance is converted back into the original object before the expressions are evaluated. To avoid the cost of object type conversions, string-formatted data items are recommended whenever possible.
When an expression is inserted or updated, Expression Filter validates the syntax and ensures that the expression refers to valid elementary attributes and functions associated with the attribute set. The SQL
EVALUATE operator evaluates expressions using the privileges of the owner of the table that stores the expressions. For instance, if an expression includes a reference to a user-defined function, during its evaluation, the function is executed with the privileges of the owner of the table. References to schema objects with no schema extensions are resolved in the table owner's schema.
An expression that refers to a user-defined function may become invalid if the function is modified or dropped. An invalid expression causes the SQL statement evaluating the expression to fail. To recover from this error, replace the missing or modified function with the original function.
The Expression Validation utility is used to verify an expression set. It identifies expressions that have become invalid since they were inserted, perhaps due to a change made to a user-defined function or table. This utility collects references to the invalid expressions in an exception table. If an exception table is not provided, the utility fails when it encounters the first invalid expression in the expression set.
The following commands collect references to invalid expressions found in the
Consumer table. The BUILD_EXCEPTIONS_TABLE procedure creates the exception table, InterestExceptions, in the current schema. The VALIDATE_EXPRESSIONS procedure validates the expressions and stores the invalid expressions in the InterestExceptions table.
BEGIN DBMS_EXPFIL.BUILD_EXCEPTIONS_TABLE (exception_tab => 'InterestExceptions'); DBMS_EXPFIL.VALIDATE_EXPRESSIONS (expr_tab => 'Consumer', expr_col => 'Interest', exception_tab => 'InterestExceptions'); END; /
A user requires
SELECT privileges on a table storing expressions to evaluate them. The SQL
EVALUATE operator evaluates expressions using the privileges of the owner of the table that stores the expressions. The privileges of the user issuing the query are not considered.
Expressions can be inserted, updated, and deleted by the owner of the table. Others must have
UPDATE privileges for the table, and they must have
EXPRESSION privileges for a specific Expression column in the table to be able to make modifications to it.
BEGIN DBMS_EXPFIL.GRANT_PRIVILEGE (expr_tab => 'Consumer', expr_col => 'Interest', priv_type => 'INSERT EXPRESSION', to_user => 'Andy'); END; /
The Expression Filter error message numbers are in the range of 38401 to 38600. The error messages are documented in Oracle Database Error Messages.
Oracle error message documentation is only available in HTML. If you only have access to the Oracle Documentation CD, you can browse the error messages by range. Once you find the specific range, use your browser's find in page feature to locate the specific message. When connected to the Internet, you can search for a specific error message using the error message search feature of the Oracle online documentation.