Pushing and pulling in XML message exchange

Whenever two systems need to "talk", the nature of the speech acts to be used raises its head.

Do I talk while you listen?
Do I ask you a question and you answer me?
Do I state a fact and broadcast it to anybody who happens to be listening?
Do I sit back and say "go on, ask me a question"?

Some of these choices can be safely relegated to implementation detail. i.e. technically speaking, numerous options can be made to work.

However, some are directly impacted by the boundaries - both physical and organisational - between the communicating parties.

In the Public Services Broker - an SOA based integration infrastructure under construction in Ireland, many of the services connected to the PSB will be hosted by agencies separated from the PSB both physically and organisationally.

As a consequence, it is necessary to analyse the various possible meessage exchange choreographies and take these "business" issues into account. The document Push and Pull Message Delivery in the PSB Architecture is a position paper on the topic.

Although the document is specific to the PSB, the questions discused have a wider applicability in any SOA based on an asynchronous messaging substrate.

Comments welcome.

I guess. Its a problem.

All guesses have bigger guesses, on their backs to bite them.
And smaller guesses within those guesses, and so on, ad infinitum.

With apologies to Augustus de Morgan and all the world's fleas.

Guesswork features in a lot of software. We like it. We want it. It makes software smart. Or does it? Deleterious guesswork in application integration is an ITWorld article that ponders the pros and cons of the guessing game we call data processing.