Feature-oriented Speciications

A feature is a part or aspect of a speciication which a user perceives as having a self-contained functional role. In large speciications there are several problems that make the manipulation of features diicult: the part of the speciication describing a feature is widely distributed over the whole speciication, and features may interact in ways that are hard to predict. To overcome these problems, we aim to construct a feature-oriented speciication language which allows the speciier to talk explicitly about features and their possible interactions. In a feature oriented speciication language, a feature speciication should be a textual unit which is easy to understand in isolation, and easy to add, remove and respecify. However, a given feature cannot be applied to any speciication; it will impose certain minimal requirements of the speciication which must hold there for the feature to make sense. Thus, a feature will be deened as a parameterised theory where the parameter represents these minimal requirements of the speciication. Using the speciication of the system in question as the actual parameter, the signature of the speciication that results from adding the feature will be given by a pushout. Whenever we add a feature, some revision of the behaviour is needed. Therefore, to construct the result speciication we need some way to deal with the overriding of some axioms. This will be done by preferential semantics of defaults.