This task topic describes how to open an existing message definition file in the Message Definition editor; you can then view and edit the contents of the file.
To open an existing message definition file:
Switch to the Broker Application Development perspective.
In the Broker Development view, right-click the message definition file (file extension *.mxsd) that you want to open, and select Open. This launches the Message Definition editor for the message definition file that you have specified.
Tip: The Eclipse framework lets you open resource files with other editors. However, you are advised to use only the workbench Message Definition editor to work with message definition files, because this editor correctly validates any changes that are made to the message definition files. Other editors might not do this.