VOSS 3.1

Where do you keep your behavior? Normalised in the application domain objects? In non-domain transaction-performing classes? Some of each? I seem to remember this question being touched on once long ago in Digitalk’s Compuserve forum, but never since.

One of the benefits of a persistent object database is that not only static integrity constraints but arbitrarily complex procedure can be expressed just once in the appropriate application domain object, rather than being scattered and/or replicated in a number of external function oriented procedures - normalisation of procedure, in other words. However, the downside of this is that if an intensively used method is located in a domain class of which there are relatively few instances, then those objects may become locking hotspots which destroy concurrency, even though they themselves may not be changed, merely carrying transactional responsibility.

At the other extreme, locating transaction procedures in non-database objects which call only get & set methods in the domain objects, maybe with simple integrity constraint methods, imposes no additional constraint on concurrency, but at the cost of additional work during application design and modification, to ensure that update transactions are all consistent with each others’ implied integrity constraints.

Design by CRC cards (class, responsibility, collaboration) would seem to identify the theoretical location of transaction responsibility, but how does this work out in practice? Are there common patterns from which guidelines might be found for these design decisions?
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