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

The Rule mediator uses an XML message as an input and produces a processed XML message after applying a set of rules. The result xml message can be used as the new soap body message. Alternatively, the information in the processed XML message can be used route the message or do any further processing. or the information can be used to route the message. The use the information to route the message or do any other processing.

Info

The Rule mediator is a content aware mediator.

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Table of Contents
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Code Block
XML
XML
<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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UI Configuration

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The Main Elements of the Rule Token

<ruleset>

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,

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

The key or inline Rule script must be defined. Otherwise, the Rule Mediator configuration will be invalid.

<session>

The Rule Session specifies the stateful or stateless behavior of the Rule engine. If this has value stateful, then the Rule engine will execute Rules in a stateful manner. For any other value, "stateless" is assumed. There are optional properties, which are used when creating the Rule Session.

Info
titleTip

Rule Session is optional and the default one is "Stateful."

<facts> / <results>

  • Facts - Specifies the facts being used in Ruleset. It also defines how to formulate facts from the message, etc.
  • Results - Defines how to handle results from the Ruleset execution. Result-adapters usually enrich the message with results. For example, if you are using POJO adapter (i.e. a Java class as the type; the class name of a result), then we transform POJO into an XML and attached to the SOAP message.

The Main Attributes of the <facts> and <results> elements:

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

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

    Info
    titleTip

    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
      titleNote

      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.

UI Configuration

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The parameters available to configure the Rule mediator are categorised into the following main elements.

Source
Parameter NameDescription
Value 
XPath 

 

The Main Elements of the Rule Mediator

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A rule script can be given as a registry key or an in-line script. To give rule script as in-lined, you can use the editor.

Rule Set options:

  • URI
  • In-lined - Allows to create or edit the Script of the Rule using the "Rule Script Editor."
  • Registry Lookup - Allows to choose the key from Configuration Registry or Governance Registry.
Info
titleTip

Source Format - XML or native.
If the language is XML, then this attribute should be XML. For any other value, the Rule Mediator assumes that the rule script is in native format. If the rule script is in native format, it should be given by wrapping as a CDATA section inside a XML tag. For example, <X><![CDATA[ native code]]></X>.

It is possible to have properties for rules set creation, registration, de-registration. There are add property options for each.

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.

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

parameters available to configure the Rule mediator are categorised into the following main elements.

Source

This section is used to enter the source from which the XML input for the mediator should be taken.

The parameters available in this section are as follows.

Parameter NameDescription
ValueThis parameter can be used to enter a static value as the source.
XPathThis parameter enables you to use an XPath expression to obtain the input facts of the message from a SOAP body, a SOAP header or a property. This XPath expression can be used to specify the message path for the relevant fact type even when creating fact objects.
Target

This section is used to enter details of the destination to which the result of the mediation should be added.

The parameters available in this section are as follows.

Parameter NameDescription
ValueThis parameter is used to enter a static value to specify the location go which the resulting message should be added.
Result XpathThis parameter is used to derive the location to which the resulting message should be added via an Xpath expression.
XpathThis parameter is used to enter a Xpath expression to specify a part of the generated result XML to be added to the target.
ActionThis parameter is used to specify whether the result XML should replace the target, or whether it should be added as a child or a sibling.

 

Rule Set

The rule set contains the rules that apply to the input and output facts based on which WSO2 BRS can create the web service WSDL. input facts are the facts that are sent by the rule service client and the output facts are the facts which are received by the client.

The parameters available in this section are as follows.

Parameter NameDescription
Rule Script As

This parameter is used to specify how you want to enter the rule script. Possible options are as follows.

  • In-Lined: If this is selected, the rule script can be added within the mediator configuration.
  • Key: If this is selected, the rule script can be saved in the Registry and accessed via a key.
  • URL: If this is selected, you can refer to a rule script via a URL.
Info

If the rule set is non-XML, you may need to wrap it with a CDATA section inside a XML tag as shown in the example below.

Code Block
XML
XML
<X><![CDATA[ native code]]></X>
Info
titleNote

The key or

...

inline Rule script must be defined. Otherwise, the Rule Mediator configuration will be invalid.

Rule

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Those are used when creating a Rule Set.

Options for Rule Set Creation Properties:

  • Name - The name of the Rule Set property.
  • Value - The type of the property value.
  • Action - Deletes the property.

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Session Type - Indicates the stateful or stateless behavior of the Rule engine:

  • Stateful - Rule engine will execute Rules in a stateful manner.
  • Stateless

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Used when creating Rule Session.

Options for Rule Session Configuration Properties:

  • Name - The name of the Rule Set property.
  • Value - The type of the property value.
  • Action - Deletes the property.

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  • New Type
  • Build-in Type:
    • message
    • dom
    • content
    • omelement
    • mediator

...

TypeThis parameter is used to specify whether the rule type is Regular or Decision Table.

 

Input Facts

Input facts are facts that are sent by the rule service client. This section contains parameters that can be used to configure the input facts. Values should be defined for the following parameters before you add the individual input facts.

Parameter NameDescription
Wrapper NameThe name of the wrapping element for all the facts.
NameSpaceThe namespace for the wrapping element.

You can click Add a Fact to add an input fact. The page will expand to display the following section.

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The parameters available to configure an input fact are as follows.

Parameter NameDescription
TypeThe fact type. You can select any of the registered fact types.
Element NameThe element name of the fact in the XML configuration.
NameSpaceThe namespace for the element.
XPathThis parameter can be used to enter an XPath expression to create an input fact using a part of the input XML.
NS EditorClick this link to edit the namespaces. Then the Namespace Editor panel would appear where you can provide any number of namespace prefixes and URLs used in the XPath expression. 
ActionThis parameter can be used to delete and existing fact.

 

Output Facts

Output facts are the facts received by the rule service client after the rules in the rule set are applied.

Parameter NameDescription
Wrapper NameThe name of the wrapping element for all the output facts.
NameSpaceThe namespace for the wrapping element.

You can click Add a Fact to add an output fact. The page will expand to display the following section.

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The parameters available to configure an output fact are as follows.

Parameter NameDescription
TypeThe fact type. You can select any of the registered fact types .
Element NameThe fact type. You can select any of the registered fact types .
NameSpaceThe namespace of the element.
ActionThis parameter can be used to delete and existing fact.
Info
titleNote

You can configure the Mediator mediator using XML. Click on " switch to source view " in the "Mediator" window.

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Example

In this example, 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 be applied.

Code Block
XML
XML
<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>

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 Excerpt
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Description of the Rule Mediator in WSO2 ESB.