Musings with John Schlesinger

John Schlesinger is an event thinker par excellence. So whenever I get the chance, I visit him in London to validate some thinking - or just to spend time with a terrific guy! So on a recent trip to London the subject turned to the rise of event thinking and the downplaying of the traditional SOA patterns. Of course the SOA traditions are being reborn to encompass the events brigade, but because SOA is so broadly and imprecisely defined that's perfectly OK. The SOA hype is over, long live the SOA hype. But that's perhaps a topic for another time.

The key observation from my lunch with John was one I had suspected, but was not able to frame properly. With a few well chosen sentences John had it for me.

This is all concerned with orchestration and control. So (deep breath), here goes. Where an event is raised and that event is to be processed by some subscriber, any intent to orchestrate the handling of the event by the subscriber results in a massive increase in complexity. (Roger Sessions will love this!). Naively one starts to think you have the "OK/Not OK pair" of possible responses. But then the "Not OK" responses blossom out of control. We have situations where the "Not OK" response must result in the retransmission of the event (and how does that happen?) and other cases where it must not. We have cases where the originator of the event has to interpret the behavior of the recipient. That sounds like some awfully nasty coupling to me. So instead of thinking that one has the "OK/Not OK" duality from the recipients view point actually what you have is the"OK/{set of lots of possible not OKs which the sender has to know about} multi-trality. In short that's just crappy design!

Thanks John