11 Advanced Rule Concepts

Rule Condition

A rule condition combines one or more expressions and conditions and returns a Boolean value, which is a value of TRUE, FALSE, or NULL (unknown). An expression is a combination of one or more values and operators that evaluate to a value. A value can be data in a table, data in variables, or data returned by a SQL function or a PL/SQL function. For example, the following expression includes only a single value:

salary

The following expression includes two values (salary and .1) and an operator (*):

salary * .1

The following condition consists of two expressions (salary and 3800) and a condition (=):

salary = 3800

This logical condition evaluates to TRUE for a given row when the salary column is 3800. Here, the value is data in the salary column of a table.

A single rule condition can include more than one condition combined with the AND, OR, and NOT logical conditions to a form compound condition. A logical condition combines the results of two component conditions to produce a single result based on them or to invert the result of a single condition. For example, consider the following compound condition:

salary = 3800 OR job_title = 'Programmer' 

This rule condition contains two conditions joined by the OR logical condition. If either condition evaluates to TRUE, then the rule condition evaluates to TRUE. If the logical condition were AND instead of OR, then both conditions must evaluate to TRUE for the entire rule condition to evaluate to TRUE.

:x = 55

is_manager(employee_id) = 'Y'

:y.z = 9

Rule Evaluation Context

An evaluation context is a database object that defines external data that can be referenced in rule conditions. The external data can exist as variables, table data, or both. The following analogy might be helpful: If the rule condition were the WHERE clause in a SQL query, then the external data in the evaluation context would be the tables and bind variables referenced in the FROM clause of the query. That is, the expressions in the rule condition should reference the tables, table aliases, and variables in the evaluation context to make a valid WHERE clause.

A rule evaluation context provides the necessary information for interpreting and evaluating the rule conditions that reference external data. For example, if a rule refers to a variable, then the information in the rule evaluation context must contain the variable type. Or, if a rule refers to a table alias, then the information in the evaluation context must define the table alias.

The objects referenced by a rule are determined by the rule evaluation context associated with it. The rule owner must have the necessary privileges to access these objects, such as SELECT privilege on tables, EXECUTE privilege on types, and so on. The rule condition is resolved in the schema that owns the evaluation context.

For example, consider a rule evaluation context named hr_evaluation_context that contains the following information:

• Table alias dep corresponds to the hr.departments table.

• Variables loc_id1 and loc_id2 are both of type NUMBER.

The hr_evaluation_context rule evaluation context provides the necessary information for evaluating the following rule condition:

dep.location_id IN (:loc_id1, :loc_id2)

In this case, the rule condition evaluates to TRUE for a row in the hr.departments table if that row has a value in the location_id column that corresponds to either of the values passed in by the loc_id1 or loc_id2 variables. The rule cannot be interpreted or evaluated properly without the information in the hr_evaluation_context rule evaluation context. Also, notice that dot notation is used to specify the column location_id in the dep table alias.

:x = 4 AND :y < :max

Rule Action Context

An action context contains optional information associated with a rule that is interpreted by the client of the rules engine when the rule is evaluated for an event. The client of the rules engine can be a user-created application or an internal feature of Oracle, such as Oracle Streams. Each rule has only one action context. The information in an action context is of type SYS.RE$NV_LIST, which is a type that contains an array of name-value pairs.

The rule action context information provides a context for the action taken by a client of the rules engine when a rule evaluates to TRUE or MAYBE. The rules engine does not interpret the action context. Instead, it returns the action context, and a client of the rules engine can interpret the action context information.

For example, suppose an event is defined as the addition of a new employee to a company. If the employee information is stored in the hr.employees table, then the event occurs whenever a row is inserted into this table. The company wants to specify that several actions are taken when a new employee is added, but the actions depend on which department the employee joins. One of these actions is that the employee is registered for a course relating to the department.

In this scenario, the company can create a rule for each department with an appropriate action context. Here, an action context returned when a rule evaluates to TRUE specifies the number of a course that an employee should take. Here are parts of the rule conditions and the action contexts for three departments:

These action contexts return the following instructions to the client application:

• The action context for the rule_dep_10 rule instructs the client application to enroll the new employee in course number 1057.

• The action context for the rule_dep_20 rule instructs the client application to enroll the new employee in course number 1215.

• The NULL action context for the rule_dep_30 rule instructs the client application not to enroll the new employee in any course.

Each action context can contain zero or more name-value pairs. If an action context contains more than one name-value pair, then each name in the list must be unique. In this example, the client application to which the rules engine returns the action context registers the new employee in the course with the returned course number. The client application does not register the employee for a course if a NULL action context is returned or if the action context does not contain a course number.

If multiple clients use the same rule, or if you want an action context to return more than one name-value pair, then you can list more than one name-value pair in an action context. For example, suppose the company also adds a new employee to a department electronic mailing list. In this case, the action context for the rule_dep_10 rule might contain two name-value pairs:

The following are considerations for names in name-value pairs:

• If different applications use the same action context, then use different names or prefixes of names to avoid naming conflicts.

• Do not use $ and # in names because they can cause conflicts with Oracle-supplied action context names.

You add a name-value pair to an action context using the ADD_PAIR member procedure of the RE$NV_LIST type. You remove a name-value pair from an action context using the REMOVE_PAIR member procedure of the RE$NV_LIST type. If you want to modify an existing name-value pair in an action context, then you should first remove it using the REMOVE_PAIR member procedure and then add an appropriate name-value pair using the ADD_PAIR member procedure.

Rule Set Evaluation Process

Figure 11-1 shows the rule set evaluation process:

1. A client-defined event occurs.

2. The client initiates evaluation of a rule set by sending information about an event to the rules engine using the DBMS_RULE.EVALUATE procedure.

3. The rules engine evaluates the rule set for the event using the relevant evaluation context. The client specifies both the rule set and the evaluation context in the call to the DBMS_RULE.EVALUATE procedure. Only rules that are in the specified rule set, and use the specified evaluation context, are used for evaluation.

4. The rules engine obtains the results of the evaluation. Each rule evaluates to either TRUE, FALSE, or NULL (unknown).

5. The rules engine returns rules that evaluated to TRUE to the client, either in a complete list or one by one. Each returned rule is returned with its entire action context, which can contain information or can be NULL.

6. The client performs actions based on the results returned by the rules engine. The rules engine does not perform actions based on rule evaluations.

Figure 11-1 Rule Set Evaluation

Description of "Figure 11-1 Rule Set Evaluation"

Partial Evaluation

Partial evaluation occurs when the DBMS_RULE.EVALUATE procedure is run without data for all the tables and variables in the specified evaluation context. During partial evaluation, some rules can reference columns, variables, or attributes that are unavailable, while some other rules can reference only available data.

For example, consider a scenario where only the following data is available during evaluation:

• Column tab1.col = 7

• Attribute v1.a1 = 'ABC'

The following rules are used for evaluation:

• Rule R1 has the following condition:

  (tab1.col = 5)
  

• Rule R2 has the following condition:

  (:v1.a2 > 'aaa')
  

• Rule R3 has the following condition:

  (:v1.a1 = 'ABC') OR (:v2 = 5)
  

• Rule R4 has the following condition:

  (:v1.a1 = UPPER('abc'))
  

Given this scenario, R1 and R4 reference available data, R2 references unavailable data, and R3 references available data and unavailable data.

Partial evaluation always evaluates only simple conditions within a rule. If the rule condition has parts which are not simple, then the rule might or might not be evaluated completely, depending on the extent to which data is available. If a rule is not completely evaluated, then it can be returned as a MAYBE rule.

Given the rules in this scenario, R1 and the first part of R3 are evaluated, but R2 and R4 are not evaluated. The following results are returned to the client:

• R1 evaluates to FALSE, and so is not returned.

• R2 is returned as MAYBE because information about attribute v1.a2 is not available.

• R3 is returned as TRUE because R3 is a simple rule and the value of v1.a1 matches the first part of the rule condition.

• R4 is returned as MAYBE because the rule condition is not simple. The client must supply the value of variable v1 for this rule to evaluate to TRUE or FALSE.

Privileges for Creating Database Objects Related to Rules

To create an evaluation context, rule, or rule set in a schema, a user must meet at least one of the following conditions:

• The schema must be the user's own schema, and the user must be granted the create system privilege for the type of database object being created. For example, to create a rule set in the user's own schema, a user must be granted the CREATE_RULE_SET_OBJ system privilege.

• The user must be granted the create any system privilege for the type of database object being created. For example, to create an evaluation context in any schema, a user must be granted the CREATE_ANY_EVALUATION_CONTEXT system privilege.

Privileges for Altering Database Objects Related to Rules

To alter an evaluation context, rule, or rule set, a user must meet at least one of the following conditions:

• The user must own the database object.

• The user must be granted the alter object privilege for the database object if it is in another user's schema. For example, to alter a rule set in another user's schema, a user must be granted the ALTER_ON_RULE_SET object privilege on the rule set.

• The user must be granted the alter any system privilege for the database object. For example, to alter a rule in any schema, a user must be granted the ALTER_ANY_RULE system privilege.

Privileges for Dropping Database Objects Related to Rules

To drop an evaluation context, rule, or rule set, a user must meet at least one of the following conditions:

• The user must own the database object.

• The user must be granted the drop any system privilege for the database object. For example, to drop a rule set in any schema, a user must be granted the DROP_ANY_RULE_SET system privilege.

Privileges for Placing Rules in a Rule Set

This section describes the privileges required to place a rule in a rule set. The user must meet at least one of the following conditions for the rule:

• The user must own the rule.

• The user must be granted the execute object privilege on the rule if the rule is in another user's schema. For example, to place a rule named depts in the hr schema in a rule set, a user must be granted the EXECUTE_ON_RULE privilege for the hr.depts rule.

• The user must be granted the execute any system privilege for rules. For example, to place any rule in a rule set, a user must be granted the EXECUTE_ANY_RULE system privilege.

The user also must meet at least one of the following conditions for the rule set:

• The user must own the rule set.

• The user must be granted the alter object privilege on the rule set if the rule set is in another user's schema. For example, to place a rule in the human_resources rule set in the hr schema, a user must be granted the ALTER_ON_RULE_SET privilege for the hr.human_resources rule set.

• The user must be granted the alter any system privilege for rule sets. For example, to place a rule in any rule set, a user must be granted the ALTER_ANY_RULE_SET system privilege.

In addition, the rule owner must have privileges on all objects referenced by the rule. These privileges are important when the rule does not have an evaluation context associated with it.

Privileges for Evaluating a Rule Set

To evaluate a rule set, a user must meet at least one of the following conditions:

• The user must own the rule set.

• The user must be granted the execute object privilege on the rule set if it is in another user's schema. For example, to evaluate a rule set named human_resources in the hr schema, a user must be granted the EXECUTE_ON_RULE_SET privilege for the hr.human_resources rule set.

• The user must be granted the execute any system privilege for rule sets. For example, to evaluate any rule set, a user must be granted the EXECUTE_ANY_RULE_SET system privilege.

Granting EXECUTE object privilege on a rule set requires that the grantor have the EXECUTE privilege specified WITH GRANT OPTION on all rules currently in the rule set.

Privileges for Using an Evaluation Context

To use an evaluation context in a rule or a rule set, the user who owns the rule or rule set must meet at least one of the following conditions for the evaluation context:

• The user must own the evaluation context.

• The user must be granted the EXECUTE_ON_EVALUATION_CONTEXT privilege on the evaluation context, if it is in another user's schema.

• The user must be granted the EXECUTE_ANY_EVALUATION_CONTEXT system privilege for evaluation contexts.

Evaluation Context for Global, Schema, Table, and Subset Rules

When you create global, schema, table, and subset rules, the system-created rule sets and rules use a built-in evaluation context in the SYS schema named STREAMS$_EVALUATION_CONTEXT. PUBLIC is granted the EXECUTE privilege on this evaluation context. Global, schema, table, and subset rules can be used by capture processes, synchronous captures, propagations, apply processes, and messaging clients.

During Oracle installation, the following statement creates the Oracle Streams evaluation context:

DECLARE
  vt  SYS.RE$VARIABLE_TYPE_LIST;
BEGIN
  vt := SYS.RE$VARIABLE_TYPE_LIST(
    SYS.RE$VARIABLE_TYPE('DML', 'SYS.LCR$_ROW_RECORD', 
       'SYS.DBMS_STREAMS_INTERNAL.ROW_VARIABLE_VALUE_FUNCTION',
       'SYS.DBMS_STREAMS_INTERNAL.ROW_FAST_EVALUATION_FUNCTION'),
    SYS.RE$VARIABLE_TYPE('DDL', 'SYS.LCR$_DDL_RECORD',
       'SYS.DBMS_STREAMS_INTERNAL.DDL_VARIABLE_VALUE_FUNCTION',
       'SYS.DBMS_STREAMS_INTERNAL.DDL_FAST_EVALUATION_FUNCTION'));
    SYS.RE$VARIABLE_TYPE(NULL, 'SYS.ANYDATA', 
       NULL,
       'SYS.DBMS_STREAMS_INTERNAL.ANYDATA_FAST_EVAL_FUNCTION'));
  DBMS_RULE_ADM.CREATE_EVALUATION_CONTEXT(
    evaluation_context_name => 'SYS.STREAMS$_EVALUATION_CONTEXT',
    variable_types          => vt,
    evaluation_function     =>
                       'SYS.DBMS_STREAMS_INTERNAL.EVALUATION_CONTEXT_FUNCTION');
END;
/

This statement includes references to the following internal functions in the SYS.DBMS_STREAM_INTERNAL package:

• ROW_VARIABLE_VALUE_FUNCTION

• DDL_VARIABLE_VALUE_FUNCTION

• EVALUATION_CONTEXT_FUNCTION

• ROW_FAST_EVALUATION_FUNCTION

• DDL_FAST_EVALUATION_FUNCTION

• ANYDATA_FAST_EVAL_FUNCTION

The ROW_VARIABLE_VALUE_FUNCTION converts an ANYDATA payload, which encapsulates a SYS.LCR$_ROW_RECORD instance, into a SYS.LCR$_ROW_RECORD instance prior to evaluating rules on the data.

The DDL_VARIABLE_VALUE_FUNCTION converts an ANYDATA payload, which encapsulates a SYS.LCR$_DDL_RECORD instance, into a SYS.LCR$_DDL_RECORD instance prior to evaluating rules on the data.

The EVALUATION_CONTEXT_FUNCTION is specified as an evaluation_function in the call to the CREATE_EVALUATION_CONTEXT procedure. This function supplements normal rule evaluation for captured LCRs. A capture process enqueues row LCRs and DDL LCRs into its queue, and this function enables it to enqueue other internal messages into the queue, such as commits, rollbacks, and data dictionary changes. This information that is enqueued by capture processes is also used during rule evaluation for a propagation or apply process. Synchronous captures do not use the EVALUATION_CONTEXT_FUNCTION.

ROW_FAST_EVALUATION_FUNCTION improves performance by optimizing access to the following LCR$_ROW_RECORD member functions during rule evaluation:

• GET_OBJECT_OWNER

• GET_OBJECT_NAME

• IS_NULL_TAG

• GET_SOURCE_DATABASE_NAME

• GET_COMMAND_TYPE

DDL_FAST_EVALUATION_FUNCTION improves performance by optimizing access to the following LCR$_DDL_RECORD member functions during rule evaluation if the condition is <, <=, =, >=, or > and the other operand is a constant:

• GET_OBJECT_OWNER

• GET_OBJECT_NAME

• IS_NULL_TAG

• GET_SOURCE_DATABASE_NAME

• GET_COMMAND_TYPE

• GET_BASE_TABLE_NAME

• GET_BASE_TABLE_OWNER

ANYDATA_FAST_EVAL_FUNCTION improves performance by optimizing access to values inside an ANYDATA object.

Rules created using the DBMS_STREAMS_ADM package use ROW_FAST_EVALUATION_FUNCTION or DDL_FAST_EVALUATION_FUNCTION, except for subset rules created using the ADD_SUBSET_RULES or ADD_SUBSET_PROPAGATION_RULES procedure.

Evaluation Contexts for Message Rules

When you use either the ADD_MESSAGE_RULE procedure or the ADD_MESSAGE_PROPAGATION_RULE procedure to create a message rule, the message rule uses a user-defined message type that you specify when you create the rule. Such a system-created message rule uses a system-created evaluation context. The name of the system-created evaluation context is different for each message type used to create message rules. Such an evaluation context has a system-generated name and is created in the schema that owns the rule. Only the user who owns this evaluation context is granted the EXECUTE privilege on it.

The evaluation context for this type of message rule contains a variable that is the same type as the message type. The name of this variable is in the form VAR$_number, where number is a system-generated number. For example, if you specify strmadmin.region_pri_msg as the message type when you create a message rule, then the system-created evaluation context has a variable of this type, and the variable is used in the rule condition. Assume that the following statement created the strmadmin.region_pri_msg type:

CREATE TYPE strmadmin.region_pri_msg AS OBJECT(
  region         VARCHAR2(100),
  priority       NUMBER,
  message        VARCHAR2(3000))
/

When you create a message rule using this type, you can specify the following rule condition:

:msg.region = 'EUROPE' AND :msg.priority = '1'

The system-created message rule replaces :msg in the rule condition you specify with the name of the variable. The following is an example of a message rule condition that might result:

:VAR$_52.region = 'EUROPE' AND  :VAR$_52.priority = '1'

In this case, VAR$_52 is the variable name, the type of the VAR$_52 variable is strmadmin.region_pri_msg, and the evaluation context for the rule contains this variable.

The message rule itself has an evaluation context. A statement similar to the following creates an evaluation context for a message rule:

DECLARE
  vt  SYS.RE$VARIABLE_TYPE_LIST;
BEGIN
  vt := SYS.RE$VARIABLE_TYPE_LIST(
    SYS.RE$VARIABLE_TYPE('VAR$_52', 'STRMADMIN.REGION_PRI_MSG', 
       'SYS.DBMS_STREAMS_INTERNAL.MSG_VARIABLE_VALUE_FUNCTION', NULL));
  DBMS_RULE_ADM.CREATE_EVALUATION_CONTEXT(
    evaluation_context_name => 'STRMADMIN.EVAL_CTX$_99',
    variable_types          => vt,
    evaluation_function     => NULL);
END;
/

The name of the evaluation context is in the form EVAL_CTX$_number, where number is a system-generated number. In this example, the name of the evaluation context is EVAL_CTX$_99.

This statement also includes a reference to the MSG_VARIABLE_VALUE_FUNCTION internal function in the SYS.DBMS_STREAM_INTERNAL package. This function converts an ANYDATA payload, which encapsulates a message instance, into an instance of the same type as the variable prior to evaluating rules on the data. For example, if the variable type is strmadmin.region_pri_msg, then the MSG_VARIABLE_VALUE_FUNCTION converts the message payload from an ANYDATA payload to a strmadmin.region_pri_msg payload.

If you create rules for different message types, then Oracle creates a different evaluation context for each message type. If you create a rule with the same message type as an existing rule, then the new rule uses the evaluation context for the existing rule. When you use the ADD_MESSAGE_RULE or ADD_MESSAGE_PROPAGATION_RULE to create a rule set for a messaging client or apply process, the new rule set does not have an evaluation context.

Purposes of Action Contexts in Oracle Streams

In Oracle Streams, an action context serves the following purposes:

• Internal LCR Transformations in Subset Rules

• Information About Declarative Rule-Based Transformations

• Custom Rule-Based Transformations

• Execution Directives for Messages During Apply

• Enqueue Destinations for Messages During Apply

A different name-value pair can exist in the action context of a rule for each of these purposes. If an action context for a rule contains more than one of these name-value pairs, then the actions specified or described by the name-value pairs are performed in the following order:

1. Perform subset transformation.

2. Display information about declarative rule-based transformation.

3. Perform custom rule-based transformation.

4. Follow execution directive and perform execution if directed to do so (apply only).

5. Enqueue into a destination queue (apply only).

   Note:

   The actions specified in the action context for a rule are performed only if the rule is in the positive rule set for a capture process, synchronous capture, propagation, apply process, or messaging client. If a rule is in a negative rule set, then these Oracle Streams clients ignore the action context of the rule.

Ensure That Only One Rule Can Evaluate to TRUE for a Particular Rule Condition

If you use a non-NULL action context for one or more rules in a positive rule set, then ensure that only one rule can evaluate to TRUE for a particular rule condition. If more than one rule evaluates to TRUE for a particular condition, then only one of the rules is returned, which can lead to unpredictable results.

For example, suppose two rules evaluate to TRUE if an LCR contains a DML change to the hr.employees table. The first rule has a NULL action context. The second rule has an action context that specifies a custom rule-based transformation. If there is a DML change to the hr.employees table, then both rules evaluate to TRUE for the change, but only one rule is returned. In this case, the transformation might or might not occur, depending on which rule is returned.

You might want to ensure that only one rule in a positive rule set can evaluate to TRUE for any condition, regardless of whether any of the rules have a non-NULL action context. By following this guideline, you can avoid unpredictable results if, for example, a non-NULL action context is added to a rule in the future.

Action Context Considerations for Schema and Global Rules

If you use an action context for a custom rule-based transformation, enqueue destination, or execute directive with a schema rule or global rule, then the action specified by the action context is carried out on a message if the message causes the schema or global rule to evaluate to TRUE. For example, if a schema rule has an action context that specifies a custom rule-based transformation, then the transformation is performed on LCRs for the tables in the schema.

You might want to use an action context with a schema or global rule but exclude a subset of LCRs from the action performed by the action context. For example, if you want to perform a custom rule-based transformation on all of the tables in the hr schema except for the job_history table, then ensure that the transformation function returns the original LCR if the table is job_history.

If you want to set an enqueue destination or an execute directive for all of the tables in the hr schema except for the job_history table, then you can use a schema rule and add the following condition to it:

:dml.get_object_name() != 'JOB_HISTORY'

In this case, if you want LCRs for the job_history table to evaluate to TRUE, but you do not want to perform the enqueue or execute directive, then you can add a table rule for the table to a positive rule set. That is, the schema rule would have the enqueue destination or execute directive, but the table rule would not.

User-Created Rules and Rule Sets

The following sections describe some of the types of rules and rule sets that you can create using the DBMS_RULE_ADM package:

• Rule Conditions for Specific Types of Operations

• Rule Conditions that Instruct Oracle Streams Clients to Discard Unsupported LCRs

• Complex Rule Conditions

• Rule Conditions with Undefined Variables that Evaluate to NULL

• Variables as Function Parameters in Rule Conditions

  Note:

  You can add user-defined conditions to a system-created rule by using the and_condition parameter that is available in some of the procedures in the DBMS_STREAMS_ADM package. Using the and_condition parameter is sometimes easier than creating rules with the DBMS_RULE_ADM package.

  See Also:

  "System-Created Rules with Added User-Defined Conditions" for more information about the and_condition parameter

:dml.get_command_type() = 'INSERT' AND :dml.get_object_owner() = 'HR' 
AND :dml.get_object_name() = 'EMPLOYEES' AND :dml.is_null_tag() = 'Y'

:dml.get_object_owner() = 'HR' AND :dml.get_object_name() = 'DEPARTMENTS' AND
:dml.is_null_tag() = 'Y' AND (:dml.get_command_type() = 'INSERT' OR
:dml.get_command_type() = 'UPDATE')

:dml.get_object_owner() = 'HR' AND :dml.get_object_name() = 'DEPARTMENTS' AND
:dml.is_null_tag() = 'Y' AND :dml.get_command_type() != 'DELETE'

BEGIN
  DBMS_RULE_ADM.CREATE_RULE(
    rule_name => 'strmadmin.dml_compat_9_2',
    condition => ':dml.GET_COMPATIBLE() > DBMS_STREAMS.COMPATIBLE_9_2()');
END;
/

BEGIN
  DBMS_RULE_ADM.CREATE_RULE(
    rule_name => 'strmadmin.dml_compat_9_2',
    condition => ':dml.GET_COMPATIBLE() <= DBMS_STREAMS.COMPATIBLE_10_1()');
END;
/

BEGIN
  DBMS_RULE_ADM.CREATE_RULE(
    rule_name => 'strmadmin.dml_compat_max',
    condition => ':dml.GET_COMPATIBLE() < DBMS_STREAMS.MAX_COMPATIBLE()');
END;
/

(:dml.get_object_owner() = 'HR' AND NOT :dml.get_object_name() = 'REGIONS')
AND :dml.is_null_tag() = 'Y' ((:ddl.get_object_owner() = 'HR' OR :ddl.get_base_
table_owner() =   'HR') AND NOT :ddl.get_object_name() = 'REGIONS') AND :ddl.is_
null_tag() = 'Y'

:dml.get_object_name() = 'Regions'

BEGIN
  -- Create the rule set
  DBMS_RULE_ADM.CREATE_RULE_SET(
    rule_set_name       => 'strmadmin.complex_rules',
    evaluation_context  => 'SYS.STREAMS$_EVALUATION_CONTEXT');
  -- Create the complex rules
  DBMS_RULE_ADM.CREATE_RULE(
    rule_name  => 'strmadmin.hr_not_regions_dml',
    condition  => ' (:dml.get_object_owner() = ''HR'' AND NOT ' ||
                  ' :dml.get_object_name() = ''REGIONS'') AND ' ||
                  ' :dml.is_null_tag() = ''Y'' ');
  DBMS_RULE_ADM.CREATE_RULE(
    rule_name  => 'strmadmin.hr_not_regions_ddl',
    condition  => ' ((:ddl.get_object_owner() = ''HR'' OR ' ||
                  ' :ddl.get_base_table_owner() =   ''HR'') AND NOT ' ||
                  ' :ddl.get_object_name() = ''REGIONS'') AND ' ||
                  ' :ddl.is_null_tag() = ''Y'' ');
  --  Add the rules to the rule set
  DBMS_RULE_ADM.ADD_RULE(
    rule_name      => 'strmadmin.hr_not_regions_dml', 
    rule_set_name  => 'strmadmin.complex_rules');
  DBMS_RULE_ADM.ADD_RULE(
    rule_name      => 'strmadmin.hr_not_regions_ddl', 
    rule_set_name  => 'strmadmin.complex_rules');
END;
/

(:dml.get_object_owner() = 'HR' AND :dml.get_object_name() LIKE 'JOB%')
AND :dml.is_null_tag() = 'Y'

((:ddl.get_object_owner() = 'HR' OR :ddl.get_base_table_owner() =      'HR') 
AND :ddl.get_object_name() LIKE 'JOB%') AND :ddl.is_null_tag() = 'Y'

:m IS NULL

:dml.get_object_owner() = 'HR' AND :m IS NULL

:m = 5

:dml.get_object_owner() = 'HR' AND :m = 5

my_function(:dml) = 'Y'

User-Created Evaluation Contexts

You can use a custom evaluation context in an Oracle Streams environment. Any user-defined evaluation context involving LCRs must include all the variables in SYS.STREAMS$_EVALUATION_CONTEXT. The type of each variable and its variable value function must be the same for each variable as the ones defined in SYS.STREAMS$_EVALUATION_CONTEXT. In addition, when creating the evaluation context using DBMS_RULE_ADM.CREATE_EVALUATION_CONTEXT, the SYS.DBMS_STREAMS_INTERNAL.EVALUATION_CONTEXT_FUNCTION must be specified for the evaluation_function parameter. You can alter an existing evaluation context using the DBMS_RULE_ADM.ALTER_EVALUATION_CONTEXT procedure.

You can find information about an evaluation context in the following data dictionary views:

• ALL_EVALUATION_CONTEXT_TABLES

• ALL_EVALUATION_CONTEXT_VARS

• ALL_EVALUATION_CONTEXTS

If necessary, you can use the information in these data dictionary views to build a new evaluation context based on the SYS.STREAMS$_EVALUATION_CONTEXT.