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The Rule Mediator is to integrate the WSO2 Rules component to the WSO2 ESB in order to define dynamic integration decisions in terms of rules.

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Syntax

<rule>

    <ruleset>
        <source [ key="xs:string" ]>
            [ in-Lined ]
        </source>
        <creation>
            <property name="xs:string" value="xs:string"/>*
        </creation>
    </ruleset>

    <session type="[stateless|stateful]"/>*

    <facts>
        <fact name="xs:string" type="xs:string" expression="xs:string" value="xs:string"/>+
    </facts>

    <results>
        <result name="xs:string" type="xs:string" expression="xs:string" value="xs:string"/>*
    </results>

    [ <childMediators>
        <mediator/>*
      </childMediators> ]

  </rule>

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The <source> is the only mandatory element of the <ruleset>. However, the properties required for the creation of the Ruleset can also be specified within <ruleset>. The key attribute is a registry "key", which is to lookup the Rule script from the registry if the rule script is in the registry. The Ruleset can be given as a child node of <source> element. If the Ruleset is non-XML, you may need to wrap it with a CDATA section inside a XML tag. For example,

<X><![CDATA[ native code]]></X>

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• "name" - The unique name.
• "value" - Represents any static value.

• "expression" - XPath expression for extracting data from the message being passed between ESB components.

  Info
  title Tip
  The default value is the first child of the SOAP Body.

• type- Defines the type of the input data. There are a few built-in types:
  • Message
  • Context
  • Map
  • POJO

  • Mediator

    Info
    title Note
    Using the rule-component.conf, you can register new types along with adapters, which are responsible for formulating specified types from the data. If there is no registered adapter for a given type, then, we assume the given type as a valid Java class name and uses POJO adapter to formulate the POJO instance whose class is the given type.

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The Main Elements of the Rule Mediator

• #Rule Rule Set
• #Rule Rule Set Creation Properties
• #Rule Rule Session
• #Rule Rule Session Configuration Properties
• #FactsFacts
• Results

Rule Set

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For example, when using the Drool native language (DRL) for rule script, it is necessary to provide a DSL file.This can be done using the attribute named source and value DRL.

<ruleSet>
   <creation>
      <property name="source" value="drl"/>
   </creation>
</ruleSet>

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Example

<rule>
        <ruleset>
        <source key="rule/sample.xml"/>
        </ruleset>
        <facts>
            <fact name="symbol" type="java.lang.String"
                  expression="//m0:getQuote/m0:request/m0:symbol/child::text()"
                  xmlns:m0="http://services.samples"/>
        </facts>
        <childMediators>
            <send>
                <endpoint>
                    <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
                </endpoint>
            </send>
                <drop/>
        </childMediators>

</rule>

In the above configuration, the Rule script is picked from the registry with key rule/sample.xml. There is one fact and it is a string variable. Its value is calculated from the current SOAP message using an expression. The Rule engine uses these facts to decide what rules should fire.