Abstract: This is the first in a series of papers dealing with the implementation of an extended term graph rewriting model of computation (described by the DACTL language) on a distributed store architecture. In this paper we set out the high level model, and under some simple packet store model is compared to a more realistic and finegrained packet store model, more closely related to the properties of a genuine distributed store architecture, and the differences are used to inspire the definition of the MONSTR sublanguage of DACTL, intended for direct execution on the machine. Various alternative operational semantics for MONSTR are proposed to reflect more closely the finegrained packet store model, and the prospects for establishing correctness are discussed. The detailed treatment of the alternative models, in the context of suitable sublanguages of MONSTR where appropriate, are subjects for subsequent papers.

Two of the currently most promising programming paradigms, namely Object-Oriented Programming and Concurrent Constraint Programming are combined into a single, highly parallel computational model based on Term Graph Rewriting Systems. In particular, we show how multi-headed Term Graph rewrite rules provide a powerful tool able to manipulate Term Graphs which themselves represent in a homogeneous way objects, concurrently executing agents and constraints. Due to the inherent fine grain parallelism of Term Graph Rewriting the proposed model is highly parallel with all activities (object communication, agent execution and constraint solving) executing concurrently. 1. Introduction The generalised computational model of Term Graph Rewriting Systems (TGRS) ([5]) has been used extensively as an implementation vehicle for a number of, often divergent, programming paradigms ranging from the traditional functional programming ones ([12,15]) to the (concurrent) logic programming ones ([3,10,18])...

The relationship between the generalised computational model of Term Graph Rewriting Systems (TGRS) and Object-Oriented Programming (OOP) is explored and exploited by extending the TGRS model with records where access to parameters is done by naming rather than position. Records are then used as the basis for expressing object-oriented techniques such as object encapsulation and (various forms of) inheritance. The effect is that TGRS with records can now be used as an implementation model for a variety of (concurrent) object-oriented (functional, logic or otherwise) languages but also as a common formalism for comparing various related techniques (such as different forms of inheritance or approaches for providing solutions to problems caused by the combination of concurrency and interaction between objects). Keywords: Object-Oriented Programming; Concurency and Parallelism; Programming Language Extensions; Rewriting Systems. Object-Oriented Term Graph Rewriting George A. Papadopoulos...

Two superficially similar graph rewriting formalisms, Interaction Nets and MONSTR, are studied. Interaction Nets come from multiplicative Linear Logic and feature undirected graph edges, while MONSTR arose from the desire to implement generalized term graph rewriting efficiently on a distributed architecture and utilizes directed graph arcs. Both formalisms feature rules with small left-hand sides consisting of two main graph nodes. A translation of Interaction Nets into MONSTR is described for both typed and untyped nets, while the impossibility of the opposite translation rests on the fact that net rewriting is always Church–Rosser while MONSTR rewriting is not. Some extensions to the net formalism suggested by the relationship with MONSTR are discussed, as well as some related implementation issues.

The extended term graph rewriting formalism of MONSTR is described, together with some of its more important rigorously established properties, particularly regarding serialisability and acyclicity. This basis is used for giving a convenient description of the global runtime structure of a concurrent object oriented language. The formalism proves especially convenient for describing very precisely a variety of intended synchronisation properties of objects in a concurrent OOL, and this flexibility is illustrated by considering a variety of possible operational semantics for a simple counter object. A lower bound object example illustrates that even more extreme synchronisation properties for objects may be contemplated without stretching the capabilities of the MONSTR formalism. The presentation is independent of any specific high level OOL. Key Words: Object Oriented Languages, Object Synchronisation, Term Graph Rewriting, MONSTR, Distributed Processing, Serialisability. 1 Introductio...

The extended term graph rewriting formalism of MONSTR is described, together with some of its more important rigorously established properties, particularly regarding serialisability and acyclicity. This basis is used for giving a convenient description of the global runtime structure of a concurrent object oriented language. The formalism proves especially convenient for describing very precisely a variety of intended synchronisation properties of objects in a concurrent OOL, and this flexibility is illustrated by considering a variety of possible operational semantics for a simple counter object. A lower bound object example illustrates that even more extreme synchronisation properties for objects may be contemplated without stretching the capabilities of the MONSTR formalism. The presentation is independent of any specific high level OOL. Keywords Object Oriented Languages, Object Synchronisation, Term Graph Rewriting, MONSTR, Distributed Processing, Serialisability. 1 INTRODUCTION...

MONSTR Rule Systems R. Banach UMCS-96-7-3 Computer Science University of Manchester Technical Report Series University of Manchester Department of Computer Science ISSN 1361 - 6161 2 A Fibration Semantics for Pi-Calculus Modules via Abstract MONSTR Rule Systems* R. Banach Department of Computer Science University of Manchester Oxford Road, Manchester, U.K. banach@cs.man.ac.uk 31 July 1996 Copyright 1996. All rights reserved. Reproduction of all or part of this work is permitted for educational or research purposes on condition that: (1) this copyright notice is included, (2) proper attribution to the author or authors is made, and (3) no commercial gain is involved. Recent technical reports issued by the Department of Computer Science, Manchester University, are available by anonymous ftp from ftp.cs.man.ac.uk in the directory pub/TR. The files are stored as PostScript, in compressed form, with the report number as filename. They can also be obtained on WWW via ...