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Showing posts from March, 2011

Single Inheritance and Other Modeling Conundrums

Sometimes a restriction in a programming language makes sense and no sense at all — all at the same time.

Modeling the real world

Think about the Java restrictions on the modeling of classes: a given class can only have one supertype and a given object's class is fixed for its lifetime.

From a programming language perspective these restrictions make a good deal of sense: all kinds of ambiguities are possible with multiple inheritance and the very idea of allowing an object to be 'rebased' fills the compiler writer with horror. (Though SmallTalk allows it.)

The problem is that, in real life, these things do happen. A 'natural' domain model is quite likely to come up with situations involving multiple inheritance and dynamic rebasing.

For example, a person can go from being a customer, to an employee, to a manager to being retired. A given person might be both an employee and a customer simultaneously (someone else may not be).

Given a domain that is as flexible as this on…