ESB vs BPEL

Both ESB and BPEL can be used for SOA implementation.

ESB (Enterprise Service Bus) implement messaging to enable services to be integrated in a message-based paradigm: both synchronous and asynchronous styles. ESB moves data via different adaptors (WebServices, FTP,File,JDBC etc) and protocols (HTTP,JMS) and enriches and transform data using XSL & domain value mapping lookups.

Oracle BPEL provides a comprehensive, standards-based and easy to use solution for creating, deploying, and managing cross-application business processes with both automated and human workflow steps.

ESB is good for routing messages to multiple destinations. It is also good for doing transformations that have little to no business rules. The footprint is much smaller and incurs minimal overhead therefore the performance is much better.

BPEL is used for bringing together multiple services. There is much more functionality and allows implementation of complex business logic.

• BPEL data transformations enrich and perform complex changes whereas ESB perform only simple transformations.
• BPEL can use Business rules, Human Workflow and Notifications, exception handling can be done in BPEL.

Use ESB when you want a really low cost solution, Only need connectivity, simple transformations and routing.

BPEL is primarily used for servies orchestration, data enrichment and human interaction.

Use BPEL+ESB when, You need to code complex business logic, integration with Workflow, complex transforms potentially involving the database or having long running processes which may or may not be stateful.

With an appropriately layered SOA architecture, one would look at ESB as a repository of services that BPEL orchestrates. At deployment time, this layered approach provides you the flexibility to dedicate servers to individual tiers (BPEL and ESB) and thereby maximize the resource usage for your particular use case.