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1

P Systems with Replicated Rewriting and Stream X-Machines (Eilenberg Machines)

100%

Aguado J. , Balanescu T. , Cowling T. , Gheorghe M. , Holcombe M. , Ipate F.

Fundamenta Informaticae

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2002

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tom Vol. 49, nr 1-3

17-33

EN

The aim of this paper is to show how the P systems with replicated rewriting can be modeled by X-machines (also called Eilenberg machines). In the first approach, the parallel behaviour of the regions of a P system is simulated by a sequential process involving a single X-machine. This allows the application of the X-machine testing procedures in order to prove the correctness of P systems. In the second approach, a P system is simulated by a communicating system of X-machines. Each component of such a system is an X-machine associated with a region of the given P system. The components act in parallel, as their counterparts do in a P system, and use some specific mechanism for communication and synchronisation.

2

Object Oriented Database with Authorization Policies

100%

Bai Y. , Varadharajan V.

Fundamenta Informaticae

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2002

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tom Vol. 53, nr 3,4

229-250

EN

Authorization specification in object oriented databases is being increasingly investigated recently by many researchers [4,5,7,9,10]. However, most of the work todate suffers from a lack of formal logic semantics to characterize different types of inheritance properties of authorization policies among complex data objects. This paper is to address this issue from a formal logic point of view. In particular, we propose a logic language that has a clear and declarative semantics to specify the structural features of object oriented databases and authorizations associated with complex data objects in databases. Our formalization characterizes the model-theoretic semantics of object oriented databases and authorizations associated with them. A direct advantage of this approach is that we can formally specify and reason about authorizations on data objects without loosing inheritance and abstraction features of object oriented databases.

3

Coloured Petri Net Modelling of an Evolving Internet Standard: the Datagram Congestion Control Protocol

88%

Billington J. , Vanit-Anunchai S.

Fundamenta Informaticae

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2008

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tom Vol. 88, nr 3

357-385

EN

The DatagramCongestion Control Protocol (DCCP) is a new transport protocol standardized by the Internet Engineering Task Force (IETF) in March 2006. This paper discusses the specification of the connectionmanagement and synchronization procedures of DCCP using Coloured Petri Nets (CPNs). After introducing the protocol, we describe how the CPN model evolved as DCCP was being developed. We focus on our experience of incremental enhancement in the hope that this will provide guidance to those attempting to build complex protocol models. In particular, we discuss how the architecture, data structures and specification style of the model evolved as DCCP was developed. We finally recommend a procedure-based style once the standard is stable. The impact of this work on the DCCP standard and our interaction with IETF is also briefly discussed.

4

Nondeterminism in Constructive Z

75%

Haghigh H. , Mirian-Hosseinabadi S.-H.

Fundamenta Informaticae

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2008

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tom Vol. 88, nr 1-2

109-134

EN

The abstraction inherent in most specifications and the need to specify nondeterministic programs are two well-known sources of nondeterminism in formal specifications. In this paper, we present a Z-based formalism by which one can specify bounded, unbounded, erratic, angelic, demonic, loose, strict, singular, and plural nondeterminism. To interpret our specifications, we use a constructive set theory, called CZ set theory, instead of the classical set theory Z. We have chosen CZ since it allows us to investigate the notion of nondeterminism from the formal program development point of view. In this way, we formally construct functional programs from Z specifications and then probe the effects of the initially specified nondeterminism on final programs. Our investigation shows that without specifying nondeterminism explicitly, the effects of the nondeterminism involved in initial specifications will not be preserved in final programs. We prove that using the new formalism, proposed by this paper, for writing nondeterministic specifications leads to programs that preserve the initially specified modalities of nondeterminism.

5

PSF - A Retrospective

51%

Veltin G. J.

Fundamenta Informaticae

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2010

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tom Vol. 100, nr 1/4

181-227

EN

Modern day computer architectures offer ever-increasing support for parallel processing, still it turns out to be quite difficult for programmers and therefore programs to tap into these parallel resources. To benefit from real general-purpose parallel computing we claim that it is likely that a paradigm shift is needed in the way we think about programming. This change of thought in turn will need to be reflected in future programming languages as well. We think that the field of process algebra provides thorough insight in how to reason about the construction of software for concurrent systems and will be one of the enabling technologies supporting this transition. The wish to connect process algebra, a mathematical theory, to the world of computer-readable and executable specifications led to the development of PSF (Process Specification Formalism). PSF is an implementation of the process algebra ACP (Algebra of Communicating Processes) integrating ASF (Algebraic Specification Formalism) to specify algebraic data types. One of the first publications on PSF appeared in Fundamenta Informaticae in 1990. Here we stated as the first sentence of the abstract: "Traditional methods for programming sequential machines are inadequate for specifying parallel systems". Unfortunately, though some advancements have been made since 1990, we can still uphold this statement 20 years later. This current report documents the developments that lead to the construction of PSF and the 1990 publication and moreover it also documents how PSF and its tools have evolved since 1990 taking the conclusion and the outlook for future work from the original article as a reference point. Using the knowledge gained both in constructing tools for PSF and in using PSF to specify concurrent systems, we will judge, discuss and criticise the design decisions taken and show paths for future developments.