Designing Diagnosable Distributed Programs.

The difficulty in debugging distributed programs motivates the development of formal methods for designing distributed programs that are easier to debug and maintain. We address state identification problem for distributed systems using the finite state I/O automaton model. A state S is identified based on the unique event sequences starting at S, called distinguishing sequences. An automaton is diagnosable if every state has a distinguishing sequence. A distributed program may not be diagnosable even if its components are diagnosable. Non-dignosable automata can, in some cases, be converted to a diagnosable form by relabelling some of its transitions in a way that preserves the semantics of the program. Not all automata can be converted to a diagnosable form in this way. This is due to inherent ill-posedness of specification. Two algorithms to convert a non-diagnosable automaton to a diagnosable form are presented. Debugging is the controlled execution of one program by another. The latter is called the supervisor of the former. The supervision operation is defined so that the debugging of a distributed program by distributed debuggers is reduced to the same as the debugging of a single program by a single debugger. An algorithm to construct a debugger for a diagnosable program is developed. Every diagnosable program has a unique debugger associated with it. This leads to the introduction of the notion of debugging complexity of programs

Creatr, a genergtic graphical distributed debugger with language support for application interfacing

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (leaves 84-86).by Shakil A. Chunawala.M.S

QUEST/Ada (Query Utility Environment for Software Testing of Ada): The development of a prgram analysis environment for Ada, task 1, phase 2

The results of research and development efforts are described for Task one, Phase two of a general project entitled The Development of a Program Analysis Environment for Ada. The scope of this task includes the design and development of a prototype system for testing Ada software modules at the unit level. The system is called Query Utility Environment for Software Testing of Ada (QUEST/Ada). The prototype for condition coverage provides a platform that implements expert system interaction with program testing. The expert system can modify data in the instrument source code in order to achieve coverage goals. Given this initial prototype, it is possible to evaluate the rule base in order to develop improved rules for test case generation. The goals of Phase two are the following: (1) to continue to develop and improve the current user interface to support the other goals of this research effort (i.e., those related to improved testing efficiency and increased code reliable); (2) to develop and empirically evaluate a succession of alternative rule bases for the test case generator such that the expert system achieves coverage in a more efficient manner; and (3) to extend the concepts of the current test environment to address the issues of Ada concurrency

Detecting and correcting errors in parallel object oriented systems

Our research concerns the development of an operational formalism for the in-source specification of parallel, object oriented systems. These specifications are used to enunciate the behavioural semantics of objects, as a means of enhancing their reliability. A review of object oriented languages concludes that the advance in language sophistication heralded by the object oriented paradigm has, so far, failed to produce a commensurate increase in software reliability. The lack of support in modern object oriented languages for the notion of 'valid object behaviour', as distinct from state and operations, undermines the potential power of the abstraction. Furthermore, it weakens the ability of such languages to detect behavioural problems, manifest at run-time. As a result, in-language facilities for the signalling and handling of undesirable program behaviours or states (for example, assertions) are still in their infancy. This is especially true of parallel systems, where the scope for subtle error is greater. The first goal of this work was to construct an operational model of a general purpose, parallel, object oriented system in order to ascertain the fundamental set of event classes that constitute its observable behaviour. Our model is built on the CSP process calculus and uses a subset of the Z notation to express some aspects of state. This alphabet was then used to construct a formalism designed to augment each object type description with the operational specification of an object's behaviour: Event Pattern Specifications (EPS). EPSs are a labeled list of acceptable object behaviours which form part of the definition of every type. The thesis includes a description of the design and implementation of EPSs as part of an exception handling mechanism for the parallel, object oriented language Solve. Using this implementation, we have established that the run-time checking of EPS specifications is feasible, albeit it with considerable overhead. Issues arising from this implementation are discussed and we describe the visualization of EPSs and their use in semantic browsing