J.UCS Special Issue on Formal Specifications of Computer-Based Systems
Václav Dvorak (Brno University of Technology, Czech Republic)
dvorak@dcse.fee.vutbr.cz
Abstract: Formal methods referring to mathematical modeling
techniques applicable to computer design, software and hardware, are
as old as computer science itself. They have gone a long way before
becoming an indispensable tool in a wide spectrum of applications,
from chip design to information system modeling. The domain of
computer-based systems (CBS) brings new challenges to formal
specification methods and tools because of complexity of CBS, which
include distributed/parallel, hard RT, safety critical and mixed SW/HW
systems.
Since complete formal specification, modeling and verification of
large complex systems is impractical at this time, using formal
methods only for the most critical portions of a system is a pragmatic
and useful strategy. The Formal Specifications Working Group within
the IEEE Computer Society TCECBS aims at the use of formal notations
to describe assumptions, requirements and a design of CBS. The first
Workshop on Formal Specifications of CBS (FS-CBS) has been organized
by Charles Rattray (UK) and Miroslav Sveda (CZ) and held in Edinburgh,
Scotland, 6-7 April, 2000. It created a forum for researchers and
practitioners from industry and academia in which discussions focused
on completed work as well as work-in-progress, related to FS CBS,
software, hardware and hardware/software applications. Authors of 17
presented contributions from Europe and North America extended their
submissions to full papers, out of which the best 6 passed the
reviewing process and appear in this special issue of J.UCS.
The paper "Nondeterministic Admissible
Interference" by J. Mullins addresses the issue of
confidentiality and information security, important for applications
such as electronic banking. Admissible information flow between
levels of multilevel security architecture is modeled using the
extended transition system DTS and completeness of such
characterization is formally proved. The followup research is to be
oriented into computeraided verification methods and tools for
admissible interference.
Two papers deal with aspects of Unified Modeling Language (UML), a
standard notation used in the objectoriented analysis and design
phase. The paper entitled "Use of E-LOTES in Adding Formality to
UML" by R. Clark and A. Moreira describes mappings from
UML constructs to the formal language ELOTOS, which then provides
executable specifications. In obtaining a formal model this way,
authors were even able to identify inconsistencies in UML
models. Rapid prototyping tools are suggested for validation
purposes. The other paper on UML, "An Outline of PVS Semantics for UML
Statecharts by I.Traore presents an approach for formalization
of
one of the multiple diagrams of UML, namely statechart
diagrams. That is achieved by using PVS Specification Language as
formal semantics domain. Formal analysis using the PVS modelchecker
makes also use of this approach.
Information system specification and design are a central problem
of information processing today. Besides UML, there are other methods
to specify data, events and processing. The paper "Modeling
Information System Behaviour with Dynamic Relation Nets by L.
Allain and P.Yim introduces a model closely related to high-level
Petri Nets - Dynamic Relation Nets (DRN). The power of DRN approach is
in the integration of both static and dynamic aspects of an
information system. The computational part of an active DBMS-based
application can be generated automatically from the DRN specification.
However, consistent design tools, dedicated to processing
specifications and based on presented ideas, are yet to be
developed.
The paper "Towards Two-Level Formal Modeling of
Computer-Based Systems by G. Karsai, G. Nordstrom, A.
Ledeczi and J. Sztipanovits argue that there is no single modeling
language, which would satisfy the requirements of all CBS. The
authors therefore propose a two-level approach, where areaspecific
modeling tools are used for creating domain-specific models, and these
tools are represented in terms of (and built from) a higher-level
meta-model. The method proved itself during years of its practical
use.
The last paper "A Survey of Formal Methods
applied to Leader Election in IEEE 1394 by S. Maharaj and C.
Shankland is a comparative study. A variety of formalisms (ELOTOS,
I/O Automata, µCRL) have been used to specify and analyze the same
real-life benchmark: IEEE 1394 FireWire multimedia serial bus and
particularly the network Leader Election (LE) protocol
specification. Specifications are judged according to their
expressiveness, readability, standardization and the kinds of analysis
possible. Comparison is by all means instructive and stimulating.
We hope that readers will benefit from the most recent work in
formal specifications and that they will get interested in formal
methods generally, and in formal specifications of CBS
specifically. Enjoyable reading!
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