State explosion is the primary obstacle to practical application of reachability analysis techniques for concurrent systems. State explosion can be substantially controlled by using process algebra to achieve compositional (divide-and-conquer) analysis. A prototype tool incorporating process algebra is described. The promise and problems of the approach are illustrated by applying the tool to an example that incorporates the alternating bit protocol as a module.

Compositional reachability analysis using process algebra

Concurrent software systems are more difficult to design and analyze than sequential systems. Considerable research has been done to help the testing, analysis, and verification of concurrent systems. Reachability analysis is a family of analysis techniques involving exhaustive examination of the whole state space. Reachability analysis is attractive because it is simple and relatively straightforward to automate, and can be used in conjunction with model-checking procedures to check for application-specific as well as general properties like freedom from deadlocks and race conditions. However, practical application of reachability analysis to real systems has been stymied by the state explosion problem, an exponential growth in the number of states to be explored as the number of processes increases.
State explosion can be substantially controlled if the analysis approach is "compositional." An analysis technique is compositional if the results of analyzing sub-systems can be "composed" to obtain analysis results for the complete system. We propose using process algebra to achieve this goal in automated analysis tools. The algebraic structure of process algebra and its rich abstraction capabilities provide the means to achieve compositional (divide-and-conquer) analysis.
The primary contribution of this dissertation will be a demonstration and evaluation of the usefulness of process algebra in controlling state explosion in reachability analysis of models close to the model of concurrency found in real programs. We propose a two-leveled approach to control state explosion--using process algebra at the coarse-grained level and simplification strategies based on a process-sleep mechanism at the fine-grained level. Although the process algebra-based compositional approach is not guaranteed to solve the state explosion problem, with a suitably modular design that provides good service abstraction, state explosion can be controlled sufficiently for application of reachability analysis to be practical.

Controlling state explosion in reachability analysis

A codesign methodology is proposed which is suitable for control-dominated systemsbut can also be extended to more complex ones. Its main purpose is to optimize thetrade-off between hardware performance and software reprogrammability andreconfigurability. The methodology proposed intends to cover the development of thewhole system. It deals in greater detail with the steps that can be made without the needfor any particular assumption regarding the target architecture. These steps concernsplitting up the specification of the system into a set of individually synthesizableelements, and then grouping them for the subsequent mapping stage. In order todecrease the complexity of each partitioning attempt, a two step algorithm is proposed,thus permitting a wide exploration of possible solutions. The methodology is based onthe TTL language, an extension of the T-LOTOS Formal Description Technique whichprovides a large amount of operators as well as a formal basis. Finally, an examplepointing out the complete design cycle, excepting the allocation stage is provided.

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Formal Codesign Methodology with Multistep Partitioning

Formal Description Techniques have been successfully experimented with for specifying and verifying concurrent systems. Generally, Formal Description Techniques are not able to specify time and probability, and are unsuitable for proving that a given system works according to desired performance requirements. For these reasons, this paper presents a language, named ELLIPSe, based on SCCS proposed by Milner providing the designer with a formal framework for reasoning about time and probability of parallel systems. An automated tool is also presented to perform the performance analysis of real systems.

A Tool for the Performance Analysis of Concurrent Systems

A tool for the automated verification of eccs specifications of osi protocols

An issue of current interest in the Open Systems Interconnection (OSI) field is the choice of a language well suited to specification and verification. For this purpose, two languages based on Milner's communication calculi are proposed, respectively intended for the specification of asynchronous and synchronous OSI systems. A formal verification method, relying upon the algebraic foundations of the two languages, is introduced and illustrated by means of examples based on nontrivial protocols and services.

G. Pappalardo

Papers

ECCS and LIPS: two languages for OSI systems specification and verification