Drools

rule-set element

Each DRL file must have exactly one rule-set element, which must be uniquely named in the rule base and declare the appropriate namespace bindings for semantic module lookup and schema validation; see Semantics Module Framework and Schema Validation.

<rule-set name="HelloWorld"
          xmlns="http://drools.org/rules"
          xmlns:java="http://drools.org/semantics/java"
          xmlns:xs="http://www.w3.org/2001/XMLSchema-instance"
          xs:schemaLocation="http://drools.org/rules rules.xsd
                             http://drools.org/semantics/java java.xsd">
  ....
  ....
<rule-set>

import element

Imports can be specified which are then available to any element that references a Class.

The body of the element can be either a fully qualified import :

<import>java.util.HashMap</import>

Or a dynamic on demand import:

<import>java.util.*</import>

application-data element

Application Data elements allow objects to be made available to conditions and consequences without the need to assert them into the Working Memory.

Application data cannot be set that is not declared in the{{rule-set}} of the rule base. To set application data:

workingMemory.setApplicationData("amount", new Integer(3));

To declare application data inside a rule-set:

<application-data identifier="amount">java.lang.Integer</application-data>

rule element

Each rule-set must contain at least one rule element. Each rule element must be uniquely named in the rule-set, and may contain optional salience and no-loop attributes. no-loop is currently ignored if the duration element is specified.

<rule name="Hello World" salience="10" no-loop="true" xor-group="group1">
  ...
  ...
</rule>

parameter element

Each rule element must contain at least one parameter element, which must use a unique name for the identifer attribute within the rule scope. By itself, the parameter element can do nothing. It requires a nested element representing an ObjectType, like class, class-field and semaphore object (or one from your own semantic module).

<parameter identifier="goodbye">
  <class>java.lang.String</class>
</parameter>

class element

The class element is an ObjectType implementation to be used inside a parameter element. It has no attributes and its contents is either a fully qualified class or a class name available from a previously imported package.

<class>java.util.HashMap</class>

<class>HashMap</class>

class-field element

The class-field element is an ObjectType implementation to be used inside a parameter element. It not only constrains the parameter to a Class, like the class element, but it also constrains to a given value for the specified field. The field is limited to String types and the value is also a static String.

<class-field field="name" value="A">State</class-field>

This is akin to saying:

<parameter identifier="state">
    <class>State</class>
</parameter>

<java:condition>state.getName().equals("A")<java:condition>

semaphore element

The semaphore element is a specialised ObjectType implementation to be used inside a parameter element. It provides global named variables, where the identifier is the global name, for use within rules; this can be useful for control execution.

To assert a semaphore without an initial value:

workingMemory.assertObject( new StringSemaphore( "state" ) );

To assert a semaphore with an initial value:

workingMemory.assertObject( new StringSemaphore( "state", "START" ) );

To specify a semaphore within a parameter

<parameter identifier="state">
    <semaphore type="String" />
</parameter>

The following supported semaphore types are:

• CharSemaphore
• DoubleSemaphore
• FloatSemaphore
• IntegerSemaphore
• ListSemaphore
• LongSemaphore
• MapSemaphore
• SetSemaphore
• ShortSemaphore
• StringSemaphore

duration element

The duration element enables Temporal Rules where Activations fire after a given time if they are still true. A duration can have can have one or more unit of time, but must specify atleast one. no-loop is currently ignored if the duration element is specified.

<duration seconds="2" />