Uma abordagem para o design de sistemas distribuídos e protocolos de comunicação.

Abstract

This work proposes an approach, based on specification styles and using the "Calculus of Communicating Systems (CCS)" algebra, for the design of distributed systems and communication protocols. Initially, the power of expression and the power of analysis of CCS algebra are employed in a classical approach based on step-by-step system development. In this context and proposed a methodology, which starts from the abstract description of the system to be developed (may be the service specification), gradually reduces this abstraction through the successive refinements (with a posteriori proof of correction), until obtaining the final specification in terms of predefined basic agents (useful for the implementation task). Such methodology is illustrated with the development of a mutual exclusion access system. Then we study the use of CCS in a transformational approach, aimed at the automation of systems development. In this context, a methodology is proposed, which employs transformation rules, to obtain the protocol entities corresponding to a service specification. Such methodology is illustrated by the development of a core part of the service and the "FileTransfer, Access and Management (FTAM)" protocol of the "International Organization for Standardization (ISO)". Finally, after a study of specification styles, a new approach is proposed, with intermediate characteristics of the classical approach and the transformational approach. In this new context, a methodology is proposed, starting from the specification of the desired service and the specification of the available service (both performed in the restriction oriented style), and obtains the specification of the corresponding protocol entities (also in the restriction oriented style). Such methodology is illustrated with the development of a communication system involving the alternating bit protocol.