A Feature Computation Tree Model to Specify Requirements and Reuse

A large subset of requirements for complex systems, services and product lines is traditionally specified by hierarchical structures of features. Features are usually gathered and represented in the form of a feature tree. The feature tree is a structural model. It represents mainly composition and specialization relations between features and does not provide the possibility to specify requirements in the form of ordering relations defined on functional features. Use case scenarios are usually employed for specification of the ordering relations. However, use case scenarios comprise isolated sequences of features, and therefore they may be inconsistent and even may contradict each other and the feature tree. Moreover, some use case scenarios defining relations on features may be incomplete. In order to support consistent specification of requirements, we suggest using a pair of related models: a feature tree model and a feature computation tree model. The pair of such related feature tree models provides the basis for the method of consistency checks of requirements. It introduces a united view on the system’s behavior at the stage of requirement specification and facilitates specification of forbidden sequences and construction complete sequences from incomplete ones. It allows designers to precisely specify the desired reuse and to find that a certain sort of reuse is not possible. Understanding already at the stage of requirements engineering that a subsystem cannot be reused without modification saves effort and money spent on development. The proposed method and models are explained using a case study of design of a system for electronic cards production