Correlations enable you to associate asynchronous messages based on message body contents. Note that not all business scenarios require correlations:

• Synchronous calls do not require correlations because the conversation context is maintained in the stack or across a TCP connection.

• Consenting BPEL processes typically correlate messages using WS-Addressing headers to pass tokens that act like session cookies in a web application. For more information, see Using WS-Addressing in an Asynchronous Service.

Correlation is required in the following scenarios. In these cases, a BPEL process must be configured to view some content of the message to select the correct process instance to receive the message.

• When using an asynchronous service that does not support WS-Addressing.

• When receiving unsolicited messages from another system.

• When the message travels through several services and the response is solicited by the initial service from the last service directly.

• When communicating through files.