When to use BPEL and ESB?

Question

Being a beginner, how should I go about deciding if a particular process has to implemented as ESB or as BPEL ?

What are the various parameters that one should use for deciding if either should be used for implementation?

Answer 1

First of all ESB is just a concept while BPEL is an OASIS standard based on XML and Web Services. A BPEL file is actually XML.

You use an ESB when you need to connect 2 or more applications together, to avoid direct point-to-point integration. This offers various benefits, such as translating messages from one format to another, or introducing other message exchange patterns. An ESB's communication is typically stateless, i.e. a message goes through, gets routed to its destination(s), and it ends there. An ESB is a very broad term, interpreted and misinterpreted by vendors to market their products.

A Business Process Management system implementing BPEL and similar technologies on the other hand are concerned with keeping track of the progress of various activities and their relationship. A BPEL process is very similar to a flow chart. A BPEL process preserves state, keeps track of its progress and flow, and is typically used (although not necessarily) in long-winded transactions which could also involve manual human tasks.

A textbook example of a BPEL process is a loan processing application. A request for a customer loan comes in, and the process first performs some automated checks using web service calls on some systems and if the credit rating is too low, the system informs a manager to evaluate the form manually (via some workflow system). The process then waits for a callback from the human workflow system, uses some correlation method (some ID) to match it with the right BPEL process instance (so that the right customer is serviced), and resumes the process accordingly.

Answer 2

ESB from my experience are always for processes that do not include a wait state. When you are just going through a list of services and will get to point a to point b without any pause states, I would use an ESB. ESBs also can handle higher quantities of message requests.

Any time human interaction is involved(Entering values, Review submission), I lean towards implementing this in a BPM. These tend to have more robust handling of long periods of waiting.