All interfaces are expressed through objects

To provide the most flexibility, the client interface to services should be through classes and the objects of those classes. Achieving this flexibility means that, among other things, messages, file formats, and data formats should never be defined as attributes of the interface. Although all these services can be used in the implementation of other services, they should never form part of another service's interface.

But simply using objects is not enough: to perform well, objects must be correctly defined. In the Taligent Application Environment objects are defined in terms not of the implementation, but of the abstraction presented to the client. It is tempting to pile everything into the class interface, but resist this urge. The key is to design the class from the client's point of view, by asking these important object-oriented design questions:

For more information, see "Reflect the client's view" on page 33 and "Express all interfaces through objects" on page 35.

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