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WSO2 BPS - Sample Guide - Flow and Links

Sample Guide - Flow and Links

Table of Content

• Objective
• Prerequisites
• Overall Idea

Objective

The activities defined inside <flow/> can be performed concurrently. But when there are can be dependencies in-between those activities. <links/>, <sources/> and <targets/> are used to define synchronization dependencies in-between those activities.

Let's understand what's meant by <links/>, <sources/> and <targets/>.

In the <flow/>, we define <links/> as follows. These link names can be sources or targets of the activities inside <flow/>

eg -

<bpel:flowname="EndlessRunningFlowOfPain"><bpel:links><bpel:linkname="transition1"/></bpel:links><bpel:sequencename="Seq1"><bpel:sources><bpel:sourcelinkName="transition1"/></bpel:sources><bpel:empty/></bpel:sequence><bpel:ifname="IfDependOnSeq1"><bpel:targets><bpel:targetlinkName="transition1"/></bpel:targets>
        .......
    </bpel:if></bpel:flow>

So using <sources/> and <targets/>, user can specify, IfDependOnSeq1 activity should be executed after Seq1.

i.e Source activity should be executed before Target activity

Note :As well there are other optional constructs to mimic conditional behavior for the <source/> and <target/>. They are

• <transactionCondition/>
  • used in <source/>
  • initialize a logical condition for the source link based on a logical condition. eg -

    <invoke...><sources><sourcelinkName="Link1"><transitionCondition>
               $tmpVar=1
            </transitionCondition></source></sources>
        ...    
    </invoke>

• <joinCondition/>
  • used in <targets/>
  • evaluates a logical condition
  • if the logical condition is true, then all the incoming sources for the defined <target/> should be true.
  • if the logical condition is false, a joinFailure exception will be thrown (Unless the target activity hasn't suppressJoinFailure=true).
    eg -

    <invoke...><targets><joinCondition>
                $Link1 and $Link2
            </joinCondition><targetlinkName="Link1"/><targetlinkName="Link2"/></targets></invoke>

Prerequisites

• Log in into BPS server admin console.
• Under Business Processes -> Add BPEL.
• Upload the TestFlowLinks.zip , (all samples are located at our sample repository.)
• Under the Business Processes -> Processes.
• Under the WSDL details widget -> Create instance

Overall Idea

Refer - TestFlowLinks.zip

Here the sample tries to implement sequence of activities inside a <flow/>, where there can be 3 execution paths based on the conditions defined in 2 and 5.
Some of the possible execution paths are

• If TransitionResolver's if condition is true and TransitionResolver2's if condition is true
  
  • 1 -> 2 -> 4 -> 5 -> 6
  • 3
  
  
• If TransitionResolver's elseIf condition is true and TransitionResolver2's if condition is true
  
  • 1 -> 2 -> 3
  • 4 -> 5 -> 6
  
  
• If TransitionResolver/s if condition is true and TransitionResolver2's if condition is false
  
  • 1 -> 2 -> 4 -> 5
  • 3
  • 6