In this paper first an evaluation and critique of current research and commercial activities on feature-based design systems is provided. To overcome the outlined limitations, we introduce SIFONIA, a module for feature-based design. Two aspects of SINFONIA are focused: the feature modeller kernel and the consistency mechanism. Due to the difficulty on finding a precise definition of the term "feature", a formal feature definition based on basic theoretical principles is given. Here, we make clear that both features and contraints are needed to describe product semantics, i.e. the two concepts cannot exist in separate. Further, a feature classification scheme for design features is provided and completed with practical examples. The maintenance of semantic correct feature-based models is an essential requirement of design-by-features applications. Semantics can be expressed by several kinds of constraints. This paper provides a set of constraint concepts from a feature-based modelling p oint of view. In regard to the different nature of feature semantics, a feature constraint classification scheme is presented. Moreover, we illustrate the different types of constraints, using simple examples. Several techniques to express and solve feature constraints are also referred.
