MQSeries does not, itself, mandate or support any particular structuring of the messages it transports.
Other products, such as MQSeries Integrator (MQSI) do offer support for messages formed as C or Cobol or as XML strings. Structured messages in MQSI are defined by a message repository. XML messages typically have a self-describing message structure and may also be managed through the repository. Messages may also be unstructured, requiring user code to parse or construct the message content. Such messages are often semi-structured, that is, they use either byte positions or fixed delimiters to separate the fields within a message. Support for such semi-structured messages is provided by the MQSeries Assist Wizard. Support for XML messages is provided through some new features to the DB2 XML Extender.