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Co- and Contra-Variance
Interoperability using contra-variance [26] for components in general is existent, if for all provided interfaces of a component (B)
- the set of provided service is a superset of the required service (of A), and
- the language of the provided protocol is a superset of the required protocol.
Vice versa for all required interfaces of A it has to be true that
- the required services nee to be a subset of the provided services, and
- the language of the required protocol is a subset of the language of the provided protocol.
If all provided and required interfaces of a component satisfy the conditions above, component interoperability is given.
Conditions for interoperability are not formulated by the PCM itself, but they are underlying assumptions on the characteristics of components and interfaces. The evaluation of interoperability constraints is not seen as a part of the model structure of the PCM, as concrete constraints for interoperability might be strategy-dependant. According with the ideas of the strategy pattern ([24][p. 315]) functions and the model itself (as a data container) are separated.
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Snowball
2007-03-16