The approach described in [JonSl, JonS3a, JonS3b] set out to extend operation decom position methods for sequential programs - such as are used in VDM [Jon90] - to cover concurrent shared-variable systems. The essential step in [JonSl] was to recognise that 1 inter/erence had to be specified. This is necessary in order to achieve a notion of compo sitionality - contrast [Owi75]. Rather than the many erudite definitions of composition ality (e. g. [ZwiSS]), the view taken here is that, when a development task is decomposed into sub-tasks, these must be simpler than the original 'task. This is easy to achieve for sequential programs: decomposing a specified operation S into (Sl; S2), the specifica tions of the Sj should neither include unnecessary information from each other nor from the context (i. e. S). An interesting discussion of the 'Quest for Compositionality' (in the context of concurrency) is contained in [dRS5, dRS6]. The rely/guarantee idea provided an existence proof that specifications and developments could be made powerful enough to cope with some forms of interference. The work initially attracted little attention but 2 3 there have recently been some critiques and attempts to extend the work Most notably, Ketil St~len's thesis [St~90] addresses the main shortcomings of [JonSl]: the fact that no attempt had been made to handle synchronization has been remedied by adding a wait condition and other limitations of expressiveness have been shown to succumb to the judicious use of auxiliary variables.

Inhalt
Theory and Foundations.- A Simpler Semantics for Z.- Interpretations of Z Schema Operators.- Promoting Forward Simulation.- Operation Schema Iterations.- Interference Revisited.- Standards and Tools.- A Tool for Defining the Architecture of Z Specifications.- CADi? Computer Aided Design in Z.- Machine support for Z: the zedB tool.- The ZIP project.- Methods.- What is a Good Formal Specification?.- Z++, An Object-Orientated Extension To Z.- Modular Object-Oriented Z Specifications.- An Approach to Object Oriented Specification using Z.- Data Flow Diagrams and Z.- Using Yourdon and Z : an Approach to Formal Specification.- A Case Study in Representing a Model: To Z or Not To Z?.- Obtaining Structural Metrics of Z Specifications for Systems Development.- Industrial Applications.- The CICS application programming interface definition.- Z! In Progress: Maintaining Z specifications.- Service Extension at the Specification Level.- Training and Education.- A Video-based Training Course in Reading Z Specifications.- A survey of Z courses in the UK.- Selected Z Bibliography.- Selected Z Bibliography.- Posters.- Metrics and Measurement of Specifications Written in Z.