Recombining changes to software specifications

This paper proposes a model of software changes for supporting the evolution of software prototypes. We decompose software evolution steps into primitive substeps that correspond to monotonic specification changes. This structure is used to rearrange chronological derivation sequences into idealized conceptual derivation structures containing only meaning-preserving (refining) changes. We indicate how this structure can be used to automatically combine different changes to a specification. A set of examples illustrates the ideas.