W.P.M. Janssen

Action systems and action refinement in the development of parallel systems

A new notion of refinement and several other new operators are proposed that allow for a compositional algebraic characterization of action systems and serializability in distributed database systems. A simple design language is introduced and is provided with a semantics essentially based on partial order models.

Layering of real-time distributed processes

An assertional proof system is proposed for a shared variable language extended with real-time constructs and synchronization, and a layering operator. The proof system is used to check real-time side conditions for an extended Communication Closed Layers rule. Reversely, this rule extends the scope of applicability of the proof system. The resulting system combines algebraic and assertional reasoning. A number of small examples are discussed.

From sequential layers to distributed processes: deriving a distributed minimum weight spanning tree algorithm

Analysis and design of distributed algorithms and protocols are difficult issues. An important cause for those difficulties is the fact that the logical structure of the solution is often invisible in the actual implementation. We introduce a framework that allows for a formal treatment of the design process, from an abstract initial design to an implementation tailored to specific architectures. A combination of algebraic and axiomatic techniques is used to verify correctness of the derivation steps. This is shown by deriving an implementation of a distributed minimum weight spanning tree algorithm in the style of [GHS].

Synchronous Development of Asynchonous Systems

Formal specifications of communicating systems should describe an abstract view of a system and hide unnecessary implementation details. A problematic implementation detail is the kind of communication used in an open or distributed system. We argue that synchronous communication is easier to use and to analyse and should be prefered over asynchronous communication at early stages of software development. Therefore we present a new class of systems that have the same semantics both with synchronous and with asynchronous communication. Such systems can be developed and verified on the basis of synchronous communication without losing an efficient asynchronous implementation. As formal framework we use CSP and develop a unified theory of asynchronous and synchronous communication in the style of [JJH90].

The compositional approach to sequential consistency and lazy caching

Summary. The lazy caching protocol proposed by Afek, Brown and Merritt [ABM93], is explained and formally proven correct by means of compositional methods. The protocol is decomposed into four simple protocols, which are of interest on their own. A top level proof is given that is to a large extent independent of the particular model used for the more detailed proofs and allows for a number of generalizations of the original lazy caching protocol. Detailed proofs of safety and liveness properties are given using CSP and trace logic.

Protocol design by layered decomposition

A version of the two phase commit protocol is formally derived from its specification. The design starts with an initial design phase that properly reflects the logical structure of the protocol as a sequence of layers. Thereafter algebraic transformations are applied, resulting in an implementation that matches the physical structure of the network. Substantial use is made of an algebraic formulation of the communication closed layers design principle.

The Primordial Soup Algorithm: a systematic approach to the specification of parallel parsers

A general framework for parallel parsing is presented, which allows for a unified, systematic approach to parallel parsing. The Primordial Soup Algorithm creates trees by allowing partial parse trees to combine arbitrarily. By adding constraints to the general algorithm, a large class of parallel parsing strategies can be defined. This is exemplified by CYK, (bottom-up) Earley and de Vreught & Honig parsers. From such a parsing strategy algorithms for various machine architectures can be derived in a systematic way.

Refining knowledge oriented actions to layered implementations

Knowledge based logics and knowledge based protocols allow to give generic specifications of network protocols and distributed algorithms in general. The question of how to transform a knowledge based program into a standard one is still large] y unsolved however. In this paper we propose two knowledge oriented actions, COMBINE and NOTIFY, that allow for the transformational development of standard protocols from knowledge based specifications and protocols. These actions combine distributed knowledge and spread knowledge respectively. Using NOTIFY and COMBINE one can give generic implementations and specifications of a large class of network protocols, and can derive implementations tailored to specific rtrchitectures in a straightforward, transformational way. The method to derive implementations relies on the notions of layering and communication closeness. It is applicable to a large class of protocols that have an underlying sequential structure. We illustrate the approach with the derivation of an algorithm to compute distances in networks and some smaller examples, aiming at implementations using asynchronous message passing. However, the method can be used in other settings as well. *This work has partially been supported by the Deutsche Forschungsgemeinschaft under grant No. 01 98/1-1. tE-mail: Wil. JanssenQinf orraat ik. uni-oldenburg. de. Cument address:TelemadcsResearch Centre, P.O. Box 589, 7500 AN, Enschede, The Netherlands. PcMiesioo to Oukedigiteubeni Gopicsof ●u or part of Ulii INtcriat fa pemosmt a ctaeemom Uee U grented without fee provided that tbe Cepiee are not ode or didfiited & rotlt or commerciet advaetage, tbe cqy! right ootice, the We of the pub lcation ●nd b &@ appear, ●nd notice u giveo tttet copyright u by permieeion of tie ACM, Inc. To cqy otberwiee, to qubtid, to pe@ 00 sewen w to sadiibuta to Me, raqutree qeeif~ ~ ~*. PODC’%, Phihdelphw PA, USA O lx ACM ~9791-~~9(j/05. .

Action Systems and Action Refinement in the Development of Parallel Systems - An Algebraic Approach

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