Maintenance of Object-oriented Systems during Structural Evolution *

We have previously developed a mathematical treatment of a calculus for class transformations that preserve or extend a set of objects. Methods for automating the maintenance of structural and behavioral consistency in systems based on evolving class structures have been provided for the object-preserving and object-extending transformations. This work extends the calculus of class transformations to include certain transformations that reflect not only the extension and reclassification of existing objects, but also structural changes (other than addition of attributes) in the original objects. Language-preserving transformations are a special case of transformations that change the structure of existing objects. If an object schema is decorated with concrete syntax, it defines not only a class structure, but also a language for describing the objects. When two schemas define the same language but different classes, the language may be used to guide the transportation of functionality between domains. The languagepreserving transformations defined here form the basis of a complete transformation system for a subset of class graphs powerful enough to express the regular languages. c 1997 John Wiley & Sons