704 research outputs found
An adequate logic for full LOTOS
We present a novel result for a logic for symbolic transition systems based on LOTOS processes. The logic is adequate with respect to bisimulation defined on symbolic transition systems
Symbolic semantics and bisimulation for full LOTOS
No abstract avaliabl
Web Services: A Process Algebra Approach
It is now well-admitted that formal methods are helpful for many issues
raised in the Web service area. In this paper we present a framework for the
design and verification of WSs using process algebras and their tools. We
define a two-way mapping between abstract specifications written using these
calculi and executable Web services written in BPEL4WS. Several choices are
available: design and correct errors in BPEL4WS, using process algebra
verification tools, or design and correct in process algebra and automatically
obtaining the corresponding BPEL4WS code. The approaches can be combined.
Process algebra are not useful only for temporal logic verification: we remark
the use of simulation/bisimulation both for verification and for the
hierarchical refinement design method. It is worth noting that our approach
allows the use of any process algebra depending on the needs of the user at
different levels (expressiveness, existence of reasoning tools, user
expertise)
Introduction to the ISO specification language LOTOS
LOTOS is a specification language that has been specifically developed for the formal description of the OSI (Open Systems Interconnection) architecture, although it is applicable to distributed, concurrent systems in general. In LOTOS a system is seen as a set of processes which interact and exchange data with each other and with their environment. LOTOS is expected to become an ISO international standard by 1988
LOTOS Symbolic Semantics in Maude
We present a formal tool where LOTOS specifications without restrictions in their data types
can be executed. The reflective feature of rewriting logic and the metalanguage capabilities of
Maude make it possible to implement the whole tool in the same semantic framework, and have
allowed us to implement the LOTOS semantics and to build an entire environment with parsing,
pretty printing, and input/output processing of LOTOS specifications
Executable Structural Operational Semantics in Maude
This paper describes in detail how to bridge the gap between theory and practice when implementing
in Maude structural operational semantics described in rewriting logic, where transitions
become rewrites and inference rules become conditional rewrite rules with rewrites in the conditions,
as made possible by the new features in Maude 2.0. We validate this technique using it in
several case studies: a functional language Fpl (evaluation and computation semantics, including
an abstract machine), imperative languages WhileL (evaluation and computation semantics) and
GuardL with nondeterminism (computation semantics), Kahn’s functional language Mini-ML (evaluation
or natural semantics), Milner’s CCS (with strong and weak transitions), and Full LOTOS
(including ACT ONE data type specifications). In addition, on top of CCS we develop an implementation
of the Hennessy-Milner modal logic for describing local capabilities of processes, and
for LOTOS we build an entire tool where Full LOTOS specifications can be entered and executed
(without user knowledge of the underlying implementation of the semantics). We also compare this
method based on transitions as rewrites with another one based on transitions as judgements
Process algebra for performance evaluation
This paper surveys the theoretical developments in the field of stochastic process algebras, process algebras where action occurrences may be subject to a delay that is determined by a random variable. A huge class of resource-sharing systems – like large-scale computers, client–server architectures, networks – can accurately be described using such stochastic specification formalisms. The main emphasis of this paper is the treatment of operational semantics, notions of equivalence, and (sound and complete) axiomatisations of these equivalences for different types of Markovian process algebras, where delays are governed by exponential distributions. Starting from a simple actionless algebra for describing time-homogeneous continuous-time Markov chains, we consider the integration of actions and random delays both as a single entity (like in known Markovian process algebras like TIPP, PEPA and EMPA) and as separate entities (like in the timed process algebras timed CSP and TCCS). In total we consider four related calculi and investigate their relationship to existing Markovian process algebras. We also briefly indicate how one can profit from the separation of time and actions when incorporating more general, non-Markovian distributions
Modelling Digital Logic in SDL
The specification of digital logic in SDL (Specification and Description Language) is investigated. A specification approach is proposed for multi-level descriptions of hardware behaviour and structure. The modelling method exploits features introduced in SDL-92. The approach also deals with the specification, analysis and simulation of timing aspects at any level in the specification of digital logic
Specifying and Refining Internal Operations in Z
Abstract An important aspect in the specification of distributed systems is the role of the internal (or unobservable) operation. Such operations are not part of the interface to the environment (i.e. the user cannot invoke them), however, they are essential to our understanding and correct modelling of the system. In this paper we are interested in the use of the formal specification notation Z for the description of distributed systems. Various conventions have been employed to model internal operations when specifying such systems in Z. If internal operations are distinguished in the specification notation, then refinement needs to deal with internal operations in appropriate ways. Using an example of a telecommunications protocol we show that standard Z refinement is inappropriate for refining a system when internal operations are specified explicitly. We present a generalization of Z refinement, called weak refinement, which treats internal operations differently from observable operations when refining a system. We discuss the role of internal operations in a Z specification, and in particular whether an equivalent specification not containing internal operations can be found. The nature of divergence through livelock is also discussed. Keywords: Z; Refinement; Distributed Systems; Internal Operations; Process Algebras; Concurrency
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