This post arises from conversations (over many years) with John Hall, the late Keith Robinson, Bob Brown, Keri Healy, Nigel Green, Richard Veryard and Fred Fickling. It has to do with how we identify things, immutability and most recently REST. So first the story(originally related to me by John Hall):
Jason has just commissioned a wonderful boat (the Argo) so he could have adventures in the Mediterranean. He commissioned a crew of likely volunteers and set sail in search of (among other things) the Golden Fleece. This was not a short voyage – in fact it lasted many years and they had many adventures – none of which are relevant to this gedanken. Like all boats (holes in the water in which you throw money), Argo needed repairing quite often. So every winter , Argo would be taken to a boatyard and refitted. Old parts were replaced, holes patched, etc.
After several years of this, there were no original parts left on the Argo at all. Everything had been replaced, even down to the smallest dowels. Question 1. Is this boat the "same" Argo as the one originally built? Certainly the crew, the local registrar of ships and taxation authorities would think so. After all, there was no need to reregister it (her, for lovers of boats). However, we know for sure it isn't the same, in fact there isn't a single original component on the boat. So, in an information system, what is the "identity" of the Argo? Does it depend on which information system (registrar/taxation/crew sign-up, repair management for example) we are thinking about?
What we didn't know, is that the wily repair shop had kept all the old parts and had been secretly reassembling them into a boat. When the final wraps came off this new boat, he announced that this was the real Argo, and that he knew the other to be a fake. Question 2. Which is the "real" Argo? Certainly this depends on who wants to know and why? The registrar of ships might well take a pragmatic point of view and decide that the repaired Argo was the "real one" and that the rebuilt one is "something else". Of course the fine piece of woodwork on which the boat's name was carefully inscribed says Argo in each case.
Question 3 (a-f and beyond). Which of our various lenses can/should we be looking at this through? The Checkland CATWOE approach becomes an important set here because the Weltanschauung (loosely translated to be the worldview) partially determines that. I suspect that the Weltanschauung is the overarching concept that allows us to choose our lenses. So what does VPEC-T say here? What does Cynefin say here? What does Systems Thinking have to say? What do Value Networks have to say?...
Question 4. Why bother? This gedanken on its own is a fun mental exercise, but there are some underlying issues that crop up time again in our real world systems. As we start to look at the world through RESTful lenses, we come head-on into representations and the state transitions of representations, and making a clear distinction between the thing and a representation of it. So we have the Argo – and then some systematic representations of Argo. When an event (a repair perhaps) happens to Argo, we may decide to change the state of the Argo representation. Or some system may decide to, while another may not. For example crew scheduling for Argo may care less about repair events than registration. So is there just one representation of Argo (with one URI) or are there many representations of Argo?
As we wrestle with the knotty problems of identification we are forced to combat our views of history – what has happened in the past to the things we care about. How we can or cannot change other people's views of the same thing (the event streams we care about when changes are made are different from other people's). We have to worry about placing ourselves at a point in time and asking questions like, "If I were asking the question last January what would your answer have been? (very useful in market research, courts of law, etc.)"
At the bottom of this is really the "who cares about what?" question and how if we attempt to create universal data models and databases of things we are doomed. Perhaps the best we can do is to keep track of the Event and Content streams as they apply to Policy, manage our own representations of things and broadcast our state changes against those representations pushing the responsibility onto the "subscribers" to decide whether they care.
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