In this article we will be discussing about various BPEL Process Activities and their usage. As the name suggests the process activities are nothing but the tasks to be performed at a specific stage. Considering a BPEL process as a workflow or a block diagram, process activities become the building blocks of BPEL Process.  

  

The most commonly used activities are Receive, Assign, Invoke, Reply, Scope, Human task, Transform, Email, Switch, Receive, Flow etc.

Lets discuss few of them in this article. We will start with Receive Activity, obvious reason being generally a BPEL process is started with this activity when a given process receives an incoming XML message.

This activity receives input from external process/adapter/service. This activity waits for an asynchronous callback response message from a service and the received message information is stored in input variable. The operation depends on the type of partner link e.g. for file adapter the receive operation with be read. I haven't used other tabs except Sensors. Sensor's can be viewed similar to triggers which can be used for monitoring the BPEL Process activity at its sub-status. Sensors can be used for various other activities as well.

The input various store the received message in XML format.

This activity allows the process to send a message in reply to a message that was received through a receive activity. The combination of a receive activity and a reply activity forms a request-response operation on the WSDL port type for the process. This is generally used in Synchronous BPEL processes when client will be given immediate response based on its input (Receive).

As the name suggests the job of this activity is to assign values of one variable to another. The variables are generally XML messages which can be manipulated and massaged in this activity.

During Assign operation one can simply assign one variable to another or apply an XPATH function to one variable and assign it to another variable. Generally every activity in an BPEL Process has input variable and output variable. Assign activity does the job taking variable values from one stage to another.

Transform

This activity enables you to create a transformation that maps source elements to target elements. This activity allows you to create an XSL (XML Stylesheet) which transforms source data elements to target data element. You can say this is much advanced assign which uses power of XSL and very good things is its just drag and drop interface to create mapping between source and target variables

Following screen will be displayed after clicking second icon in-front of Mapper file.

 Scope activity can be treated as PLSQL Block or try/catch block with set of activities performed within itself. This Block has its own set of input and output variable. With-in one scope there can be multiple Process activities

Above scope icon can be expended to see set of activities inside

One can define variables applicable for given scope by clicking (X) icon at top left of scope box

Exception handling can be associated with a scope activity. One can create a Catch branch by clicking Catch icon on the left edge of scope block and perform exception handling activities.

This is similar to case statement in any programming language. We can define various conditions based on which activities can be performed.This can have one or more conditional branches defined in a case branch, followed optionally by an otherwise branch.

Click on top portion to define the case expression

The case expressions can be defined using expression builder by clicking the Icon in-front of expression

Flow activity allows you to specify one or more activities/set of activities to be performed simultaneously. A flow activity completes when all activities in the flow have finished processing. Completion of a flow activity includes the possibility that it can be skipped if its enabling condition is false. In the diagram below Quotation is requested from two manufacturers simultaneously.

Invoke

This activity is used to call an external process using partner link/Adapter service.

The input variables are used to pass parameters/information to the called partner service and output variable is used to capture the result returned by the service.e.g. if you are calling a database procedure with input parameters and output parameters using database adapters then we can map these parameters with BPEL Invoke Activity input and output variables. Activity is intelligent enough to detect the operation in the called partner link service and enables input and output variable text boxes accordingly based in presence of request and response variables of the called partner service.

Human tasks are used for monitoring or approval activities. These tasks are displayed in BPEL Worklist application. This is bit complicated activity and can need to separate article to address creation of human task and creation of JSP pages for performing some updates on incoming XML messages. Please note (FYI) that these JSP pages can be created automatically using JDeveloper but they don't get deployed successfully when you deploy the BPEL Process to SOA Suite/Application Server, this gives some error. Hence after creating BPEL Process and related JSP pages, JSP pages need to be deployed as separate Web Project.

When Human task is created it automatically creates two transform, one invoke and one receive activity which are visible after expanding OrderApproval_1 Human task

Following things are important while defining Human Task.

1.Outcome (e.g.APPROVE,REJECT)

2.Parameters - This will be displayed in Task List and we can build JSP pages to make changes in these input parameter values before assigning final outcome.

3.Assignment and Routing Policy - This is used for sending notifications to Approving authority Person or group.

Most of the BPEL processes use the activities which discussed above. As a suggestion, I would like to insist that the best way of understanding BPEL/ESB is developing SOA Order Booking Application end-to-end step by step as mentioned in SOA Suite Tutorial (B28937-01). This will guide you various aspects of BPEL and ESB projects and how both can be integrated with each other. One can take 2-3 days to complete this 370 page tutorial end-to-end, step-by-step just make sure you follow all steps as it is without even modifying variable names.

1.BPEL Process Manager Developers Guide (B28981-03)

2.SOA Suite Tutorial(B28937-01)

 

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