Graphical Development of Consistent System Specifications Bernhard Schätz * Heinrich Hußmann ‡ Manfred Broy * *) Technische Universität München, Arcisstraße 21, 80333 München, Germany Email: broy@informatik.tu-muenchen.de, schaetz@informatik.tu-muenchen.de ‡) Siemens AG, Public Communication Networks, Advanced Development, Hofmannstraße 51, 81359 München, Germany Email: hussmann@oenzl.siemens.de Abstract . While formal methods have promised essential benefits for the software development process, industrial development reality nevertheless relies mainly on informal and especially graphical description techniques. This article argues that formal techniques are indeed useful for practical ap- plication, but they should be put to indirect use. To demonstrate this ap- proach, two pragmatic graphical description techniques, taken from the field of telecommunication, are analyzed regarding their information con- tent and their application in the process of specification development; as a result these techniques are formally defined. Based on the formal definition, “safe” development steps and their graphical counterparts are introduced. This yields a graphical development method which relies on precise formal foundations. 1 Introduction Informal graphical description methods have found wide-spread application in industry. Theoreticians have often criticized these methods for their lack of a precise definition of their conveyed information. However, for industrial practice the intuitive compre- hendability of graphical methods makes them well-suited for a fast development of high-quality software. Formal approaches provide a high degree of semantic precise- ness. In an industrial context, nevertheless, they can be applied only to a small num- ber of carefully selected projects with specially trained personnel. This gap between