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Using rules can be a very powerful tool for implementing complex logic, but the use
of rules can affect your application design. For more information on the Rules Manager,
please refer to the Oracle documentation.
The Expression Filter
The Expression Filter, available since Oracle Database 10g, uses the Rules Manager
to work with expressions. An expression is another object type that contains
attributes evaluated by the Expression Filter. You add a VARCHAR2 column to a
table that stores the values for the attributes of an expression, use a PL/SQL built-in
package to add the expression to the column, and use standard SQL to set the values
for the expression. To compare values to an expression, you use the EVALUATE
operator in the WHERE clause of your SQL statement.
Expressions can be used to define complex qualities for rows, since an expression
can have many attributes. You can also use expressions to implement many-to-many
relationships without an intermediary table by using expressions from two tables to
join the tables.


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