What should be the format and structure of a message?

A plain string? A URI or ivorn? XML?

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I'd rather define messages semantically (message name & parameters), and leave the structure and format to whatever messaging fabric happens to be being used to transport the message at that point. Maybe IDL (the other one - Corba's Interface Definition Language) would be a good, neutral, way of defining the message signatures.

Taking this approach makes messages easier to produce and consume - a client can use an existing off-the-shelf messaging library, without needing additional xml-constructing and xml-parsing steps to decode the message.

maybe the proposed messaging standard (and plastic for that matter) are best characterized as a meta-messaging standard - a way of bridging existing different messaging systems? -- NoelWinstanley_