There are 29 message header fields in a WebSphere MQ message. Message header fields include MsgId, Format, PutTime, PutDate, and other message descriptor fields.

The MsgId field is a primary key field in MQSeries source definitions. It uniquely identifies one message from another within a message queue. When you use an associated source definition to define the message data, the Designer uses the MsgId port from the header fields to associate the WebSphere MQ source with the message data. This association occurs in the MQ Source Qualifier.

When you pass the message header fields through an MQ Source Qualifier, you can also use the message header fields to filter messages that PowerCenter reads from the message queue. For example, a message queue may contain messages from several applications or messages in several formats. You can create a filter condition in the MQ Source Qualifier that allows the PowerCenter Integration Service to only read messages from a particular application and messages of a particular format.