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On Tue, 2004-06-08 at 12:56, John Cowan wrote: > Henrik Martensson scripsit: > > > For the record, if two systems exchange information, and changes in one > > system mean that the exchange format has to change, the systems are > > _not_ loosely coupled. There has been a tendency in this thread to > > equate "loose coupling" with "ignoring changes in couplings", but this > > is wrong. Loosely coupled systems must still play by the rules they have > > agreed on. > > In a really loosely coupled system, like Walter's, the "sender" has no > clue that the "receiver" even exists, still less is there any agreement > between them. The sender has published something, and the receiver must > make do as best he can. There is still a contract. If I publish an interface to a service, then I must stick to that interface. If I want people to continue using my service, I have better not break backwards compatibility too often. With XML documents, as with software APIs, you can often add new things without breaking backwards compatibility. Then again, just as with software APIs, quite frequently you can't. /Henrik
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