Each message set that you create specifies a domain, which determines the parser that is used when parsing and writing all messages that are defined within that message set. Each domain is suited to a particular class of messages (fixed-length binary, delimited text, XML, and so on). Additionally, some domains support several physical formats (sometimes called wire formats). Before you create a message set, decide which domain and physical format to use.
Alternatively, you can specify your own domain. Specify your own domain if you are using WebSphere Message Broker, and you have written a user-defined parser to parse your messages, instead of using the supplied parsers.