127 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
- Overview
- Security Model
Summary of DBMS_RULE Subprograms

Using DBMS_RULE

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

Overview
Security Model

Overview

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

See Also:

Chapter 257, "Rule TYPEs" for more information about the types used with the DBMS_RULE package
Chapter 128, "DBMS_RULE_ADM" and Oracle Streams Concepts and Administration for more information about this package and rules

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 127-1 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 127-2 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.

See Also:

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 127-3 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:

TRUE rules, which is the list of rules that evaluate to TRUE based on the given data. These rules are returned either in the OUT parameter true_rules, which returns all of the rules that evaluate to TRUE, or in the OUT parameter true_rules_iterator, which returns each rule that evaluates to TRUE one at a time.
MAYBE rules, which is the list of rules that could not be evaluated for one of the following reasons:
- The rule refers to data that was unavailable. For example, a variable attribute "x.a.b" is specified, but no value is specified for the variable "x", the attribute "a", or the attribute "a.b".
- The rule is not simple enough to be evaluated fast (without SQL) and simple_rules_only is specified as TRUE, or partial data is available.
Maybe rules are returned either in the OUT parameter maybe_rules, which returns all of the rules that evaluate to MAYBE, or in the OUT parameter maybe_rules_iterator, which returns each rule that evaluates to MAYBE one at a time.

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:

The CLOSE_ITERATOR procedure in the DBMS_RULE package is run with the iterator specified.
The iterator returns NULL because no more rules evaluate to TRUE or MAYBE.
The session in which the iterator is running ends.

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

Have EXECUTE_ON_RULE_SET privilege on the rule set
Have EXECUTE_ANY_RULE_SET system privilege
Be the rule set owner

Note:
The rules engine does not invoke any actions. An action context can be returned with each returned rule, but the client of the rules engine must invoke any necessary actions.
See Also:
- Chapter 257, "Rule TYPEs" for more information about the types used with the DBMS_RULE package
- GET_NEXT_HIT Function
- CLOSE_ITERATOR Procedure

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 127-4 GET_NEXT_HIT Function Parameter

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

Usage Notes

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:

Chapter 257, "Rule TYPEs" for more information about the types used with the DBMS_RULE package
EVALUATE Procedures
CLOSE_ITERATOR Procedure