An object-oriented approach to formal specification of reactive systems is described. The main contributions of the work are: a language for specifying and implementing reactive modules; inheritance operations for such specifications and implementations; a formal semantics for such reactive programs and for the inheritance operations in terms of partial orders of events; treatment of specifications as types of modules and treatment of modules as first-class objects; and discussion of subtyping among specifications.>

We describe a general module language integrating abstract data types, specifications and object-oriented concepts. The framework is based on the Standard ML module system, with three main extensions: subtyping, a form of object derived from ML structures, and inheritance primitives. The language aims at supporting a range of programming styles, including mixtures of object-oriented programming and programs built around specified algebraic or higher-order abstract data types. We separate specification from implementation, and provide independent inheritance mechanisms for each. In order to support binary operations on objects within this framework, we introduce "internal interfaces" which govern the way that function components of one structure may access components of another. The language design has been tested by writing a number of program examples; an implementation is under development in the context of a larger project. 1 Introduction This paper describes a general module sys...

The authors present a methodology for formal specification and prototype implementation of Ada packages using the Anna specification language. Given the formal specification of a package resulting from the methodology for package specifications, the methodology allows implementors of packages to follow a few simple steps to implement the package. The implementation is meant to be a prototype. This methodology for specification and implementation is applicable to most Ada packages. Limitations of this approach are pointed out, and software tools which help the process of specification and implementation are presented.>

The authors describe the use of formal specifications and associated tools in addressing various aspects of software maintenance-corrective, perfective, and adaptive. They also address the refinement of the software development process to build programs that are easily maintainable. The task of software maintenance in this case includes the task of maintaining the specification, as well as the program. The authors focus on the use of Anna, a specification language for formally specifying Ada programs, to aid in maintaining Ada programs. The techniques are applicable to most other specification language and programming language environments. The tools of interest are (1) the Anna Specification Analyzer, which permits analysis of the specification for correctness with respect to the informal understanding of program behavior; and (2) the Anna Consistency Checking System, which monitors the Ada program at run time on the basis of the Anna specification.>