Helmuth Partsch

Program Transformation Systems

Interest is increasing in the transformational approach to programming and in mechanical aids for supporting the program development process. Available aids range from simple editorlike devices to rather powerful interactive transformation systems and even to automatic synthesis tools. This paper reviews and classifies transformation systems and is intended to acquaint the reader with the current state of the art and provide a basis for comparing the different approaches. It is also designed to provide easy access to specific details of the various methodologies.

Existential Quantifiers in Abstract Data Types

Hierarchies of abstract data types are specified by axioms which are positive formulas consisting of universally and existentially quantified disjunctions and conjunctions of equations. Necessary and sufficient conditions for the existence of terminal algebras are investigated. Furthermore, some advantages of disjunctions and existential quantifiers within the laws are discussed and the usefulness of terminal algebras is demonstrated by a few examples.

Structuring transformational developments: a case study based on Earley's recognizer

Abstract In order to make transformational developments of programs more transparent and thus better suited e.g. for communication, it is necessary to develop more concise notations for expressing the underlying principles. By means of a non-trivial case study dealing with Earleys context-free recognition algorithm, the paper aims at providing a better understanding of fundamental concepts involved in transformational derivations.

From Requirements to their Formalization - A Case Study on the Stepwise Development of Algebraic Specifications

The paper aims at demonstrating that the concept of algebraic abstract data types together with a suitable development methodology is suited for the specification of larger programs, too. Possible phases in a stepwise, goal-oriented development of such a formal, algebraic specification out of informal requirements are exhibited along with the sample specification of a program transformation system. This development is guided by a continuous communication between the specifier and his client where additional valuable hints are provided by the formal properties of algebraic types. It turns out that the formal techniques already developed within the CIP project at the Technical University Munich also apply to this front end of the transformational activities.

An exercise in the transformational derivation of an efficient program by joint development of control and data structure

Abstract Formal program development by transformations comprises not only transitions between equivalent control constructs but also suitable changes of data structures. In principle these two (conceptually different) kinds of derivation steps can be done rather independent of each other. If, however, efficient programs are aimed at, it is vitally important to suitably intertwine them in order to benefit from their mutual influence. For this way of ‘joint development’ the paper aims at elaborating a kind of guide-line the practical use of which is illustrated by means of a non-trivial example.

Transformational Derivation of Parsing Algorithms Executable on Parallel Architectures

Comparatively few work has been published on how to construct correct parsing algorithms that are profitably executable on parallel architectures. We advocate transformational programming as a suitable methodology for the derivation of such “parallel algorithms” and illustrate our ideas by means of a comprehensive case study: Starting from a formal specification - actually the usual problem definition from Formal Language Theory - we derive by simple correctness-preserving transformations a version of the Cocke-Kasami-Younger parsing algorithm that is suited for execution on a vector machine.

Special Transformation Techniques

There are certain simple types of recursion allowing to be transformed immediately into usual iterative language constructs. On the other hand there are also routines which can only be implemented in full generality by using a stack mechanism. One of the great advantages of methods for program development is the individual and thus adequate treatment of routines — especially of recursive ones — by means of a repertory of transformation techniques. Some of the techniques based on the fundamental method of function inversion are presented in this paper.

From informal requirements to a running program: a case study in algebraic specification and transformational programming

Abstract Algebraic specification and transformational programming have been advocated as new approaches to the development of software, in order to solve some of the technical problems in software engineering such as “early validation”, correctness of implementations, re-usability of software, or re-usability of software design. By means of a nontrivial example, viz an interactive text editor, we demonstrate that the combined use of these approaches allows to bridge the gap between verbally stated requirements and a running program, even for non-toy, realistic problems.

On the Use of Algebraic Methods for Formal Requirements Definitions

By analysing various statements from the respective literature a set of criteria for good requirements definitions is extracted. It is shown that algebraic tools provide a reasonable basis for this important part of software engineering. The general statements are additionally justified by employing these algebraic methods in a comprehensive treatment of a non-trivial example, viz. part of a real-life interactive editor.

Abstract Data Types as a Tool for Requirement Engineering

Abstract data types represent a means for a modularized and abstract formal specification of programs. But there remains the problem of requirement engineering, that is, of the derivation of the abstract types from the user’s informal problem description. The paper suggests a methodology, where results from the theory of abstract data types are employed as guidelines for this derivation process.