Behaviour-preserving transformations in SHE: a formal approach to architecture design

SHE (Software/Hardware Engineering) is an object-oriented analysis, specification and design method for complex reactive hardware/software systems. SHE is based on the formal specification language POOSL and a design framework guiding the analysis and design activities. During analysis several graphical models are produced. These models are formalized in a textual representation in the POOSL language. The obtained POOSL description describes both behaviour and initial system structure. During design the initial system structure may have to be adjusted or refined due to architectural constraints and design decisions. For this purpose so-called behaviour-preserving transformations are used. These transformations allow structure modifications in a graphical way and they allow the automatic change of the POOSL specification during interactive system simulation. This paper reports the development of a formal basis for design transformations and shows their applicability.