Pymma about BPEL Compensation

Another great technical paper from Pymma Consulting:

http://www.pymma.com/eng/IT-Tech-Papers/Pdf-folder/BPEL-Compensation-complet-guide

"Every Thing You Always Wanted to Know About BPEL Compensation But Were Afraid to Ask ;-).
BPEL compensation is one of the main feature used to provide consistency in a business process. Unfortunately, BPEL tutorials often skip this part of Oasis specifications. Even if on Internet you can find papers on that topic, few propose a complete and progressive explanation with simple exercises. It is the reason why we decided to write a complete tutorial which covers all the features defined in BPEL Specifications. We hope that this paper will be useful for you. Please send us your feedback and your comment."

Download from here.

What BPEL stands for?

I have been involved in several projects where one recurring request was to "use BPEL", or more generically "to implement some level of Business Process Management (BPM)". BPEL means Business Process Execution Language and the OASIS Standard defines it as:

"WS-BPEL provides a language for the specification of Executable and Abstract business processes. By doing so, it extends the Web Services interaction model and enables it to support business transactions. WS-BPEL defines an interoperable integration model that should facilitate the expansion of automated process integration in both the intra-corporate and the business-to-business spaces."

An extended definition of SOA says:

"Service-oriented architectures (SOA) promise to implement composite applications
that offer location transparency and segregation of business logic. Location
transparency allows consumers and providers of services to exchange messages
without reference to one another’s concrete location. Segregation of business logic
isolates the core processes of the application from other service providers and
consumers."
(from: Implementing Service-Oriented Architectures (SOA) with the Java EE 5 SDK - Sun Microsystems)

So basically BPEL allows to segregate business logic into pieces of reusable sequences of atomic business activities, expressed through an XML syntax. SeeBeyond and Sun JavaCAPS 5.1 supported the BPEL 1.x standard through the eInsight engine, while the new, opensource Sun OpenESB supports BPEL 2.0., but there are of course many other products from different vendors.

However the point is that BPEL is about "segregation of business logic", it is not about "arrow and boxes programming". I underline this because I am seeing many projects where BPEL is very misused and abused: they are kind of replacing Java with BPEL because the latter is more buzzword-oriented and all those arrows and boxes look nicer. But then it happens that resulting BPEL is just polluted by technical activities, while I'm stressing the fact it should contain pure business logic. So my hint is to always put your orthogonal concerns (logging, error handling, auditing, etc...) somewhere else and leave your BPEL as clean as possible. For example, with OpenESB (commercially aka JavaCAPS 6) there is a nice JavaEE-SE which is the JBI Service Engine to execute EJBs (practically, it is a JBI bridge to the below application server). Here is a list of all JBI components you can use, have a look at Aspect SE, Camel SE (Apache Camel Service Engine) and Scripting SE for other very interesting opportunities to avoid messing-up your business logic...

Java CAPS - eInsight Business Processes Correlation HowTo

The Java Composite Application Platform Suite

The Java Composite Application Platform Suite (Java CAPS) allows companies to assemble large-scale applications built on existing systems and infrastructure. Java CAPS is an application-level network that unifies connectivity among people, application systems, and devices in different locations and across organizations. Business services facilitate the implementation of extended applications. Service oriented architectures (SOA) clarify design and enable reuse by sharing logic and data among different client systems and users.

eInsight and Java CAPS

eInsight is a component of Java CAPS. eInsight delivers Business Process management features and functions to Java CAPS. Business Process management is a strategic orchestration of the movement of information and the flow of complex processes between participants (systems, users, and organizations) to accomplish larger business objectives. eInsight uses the standard BPEL language to describe processes

1 Introduction

eInsight provides the means for matching existing Business Process instances to messages that are arriving into a Business Process. Correlation keys are individual data values contained within both the incoming message and the eInsight engine. When arriving messages contain data that matches the configured correlation keys, unique Business Process instances then continue processing on to the next step of a given Business Process.

2 Message Correlations

A correlation key is a value that you can assign to a Business Process, like a Purchase Order number. The correlation key provides a way to associate and route information about specific Business Process instances. For asynchronous message exchange between components, you must implement correlation of the instance identification.

An example of when you use asynchronous message exchanges is when you create a Receive Activity in the middle of a Business Process.

To have the correlation mechanisms working properly, right correlation keys are mandatory.

3 Example 1 - File trigger

In this scenario we have a calling process that sends a JMS message to another process and then waits for a reply, correlating instances through a unique ID.

Invoked Process - bpReplier

The bpReplier process is called from the main one. It is very simple for this example: it just copies the Jms Correlation ID and adds some information in the text field.

Main Process

The main process reads a correlation ID from a file, set it into the CorrelationID field of JMS->MessageProperties and then sends the message to the above mentioned bpReplier. An “Event Based Decision” waits for events: one it is a JMS.receive, second is a “Timer Event” in case nothing is received within a fixed amount of time.

Correlation key

The correlation key is made of two aliases:
* /Message/MessageProperties/CorrelationID
* /FileTextMessage/text


The correlation is used in two activities in the BP:
1 - FileClient.receive - with Initialize Set ='yes'
2 - JMS.receive (in the event based decision) - with Initialize Set='No'

4 Example 2 - JMS trigger

The second example shows how to use correlation in a process triggered by a JMS message instead of a file. The invoked service remains the previous simple "bpReplier", while the main process is slightly different.

Main Process

In this case the main process is split in two: first the trigger, which reads from a file and uses its internal BPID as the CorrelationID for the JMS message:

Second, the “real” main process:

This receives the above message, initializes the correlation key, send a message to the bpReplier (copying the received CorrelationID) and the waits for an event. The JMS.receive, which uses the correlation key but does not initialize it, in the event based decision correlates inbound messages, while the usual Timer Event would raise a timeout in case of long inactivity.

In this case, as we only have one kind of inbound event (a JMS message is received) the only necessary alias for the correlation key is:
/Message/MessageProperties/CorrelationID

Resources

* Sun Java CAPS public forum
* Product's official documentation