Formal Description Technique LOTOS Research Articles

Study of the characteristics of CT-Equivalence with proves

Semantic between process specifications is essential for various phases of the development of computer/telecommunications protocols as well as other systems. This includes the verifications of the refined communicating entities and their underlying service provider against their service specifications. It includes also checking the of competing designs while developing the National or International Standards. Also, it is needed in transforming a specification given in the algebraic International Standardization Organization (ISO) Formal Description Technique (FDT) Lotos into an equivalent version given in the ISO FDT Estelle or the FDT SDL (Specification and Description Language) developed by the Telecommunications Standardization Section of the International Telecommunications Union (TSS/ITU). Nevertheless, often in conformance testing/certification testing of the final products this is needed to facilitate the derivation of testing sequences. In the literature, there are many notions for that aim at ratifying the problem of equivalence. In this paper, we study the characteristics of Conformance Testing (CT) Equivalence. We prove that CT Equivalence ratifies significant problems with the other notions of semantic equivalence in the literature. We prove that CT Equivalence is a congruent and develop an application of it in verification.

Formal method for automated testing data flow aspects of communications protocols, software, and systems specified in Lotos

In this paper, we discuss the testing of data flow aspects of communications protocols and distributed systems specified in Lotos; the ISO Formal Description Technique (FDT). We also develop a method for automated derivation of sequences to conformance test data flow aspects of a system specified in Lotos. This has applications for communications protocols, software, and distributed real time systems in general. We generalize the testing method, with best known coverage, developed for Extended Finite State Machines (EFSMs) to the algebraic FDT Lotos. The method firstly constructs a Data-Oriented Restricted Behavior Tree that represents the behavior of the given specification. An algorithm for the automated construction of T is developed in this paper. Then, the testing sequences are driven.

A Formal Framework for Viewpoint Consistency

Multiple Viewpoint models of system development are becoming increasingly important. Each viewpoint offers a different perspective on the target system and system development involves parallel refinement of the multiple views. Viewpoints related approaches have been considered in a number of different guises by a spectrum of researchers. Our work particularly focuses on the use of viewpoints in Open Distributed Processing (ODP) which is an ISO/ITU standardisation framework. The requirements of viewpoints modelling in ODP are very broad and, hence, demanding. Multiple viewpoints, though, prompt the issue of consistency between viewpoints. This paper describes a very general interpretation of consistency which we argue is broad enough to meet the requirements of consistency in ODP. We present a formal framework for this general interpretations highlight basic properties of the interpretation and locate restricted classes of consistency. Strategies for checking consistency are also investigated. Throughout we illustrate our theory using the formal description technique LOTOS. Thus, the paper also characterises the nature of and options for consistency checking in LOTOS.

Viewpoints and consistency: translating lotos to Object- z

This paper presents a translation between the formal description technique lotos and the object-oriented specification language Object- z. The need for such a translation lies in the use of formal methods in viewpoint specification, and in particular in the Open Distributed Processing standard. The use of viewpoints as a set of partial interlocking specifications brings an obligation to check the consistency of these partial specifications, and to do so we need to relate specifications written in differing languages. The work presented here aims to support the consistency checking of viewpoints written using formal methods by defining a translation from lotos to Object- z. A lotos specification describes both an ADT component and a behavioural model, the former is translated into the z type system, and the behavioural specification is translated into a collection of Object- z classes where we relate lotos actions to operations in the Object- z specification. A case study is presented, illustrating the translation and consistency checking techniques discussed in the paper.

Strategies for consistency checking based on unification

There is increasing interest in models of system development which use Multiple Viewpoints. Each viewpoint offers a different perspective on the target system and system development involves parallel refinement of the multiple views. Multiple viewpoints though, prompt the issue of consistency between viewpoints. This paper describes an interpretation of consistency which is general enough to meet the requirements of consistency for very general viewpoints models. Furthermore, the paper investigates strategies for checking this consistency definition. Particular emphasis is placed on mechanisms to obtain global consistency (between an arbitrary number of viewpoints) from a series of binary consistency checks. The consistency checking strategies we develop are illustrated using the formal description technique LOTOS.

Formal Design of a Concurrent Control Algorithm for Replicated Data in Groupware Applications

One of the most important characteristics of a cooperative work system with a synchronous communication is that must sustain multiple accesses, that is to say several user writing and reading simultaneously in the same set of data. Under this premise is presented a exhaustive study of the mechanisms and algorithms of concurrent control which are described and validated formally through the employment of the formal description technique LOTOS, and detected a series of lack in their attempt by sustaining an access simultaneous to a same set of data. In this way are shown the designed, description and validation formal of an algorithm of capable concurrent control of permitting the simultaneous access to a same joint of data, reducing the conflict conditions and the need of rescinding and remakeing operations that they have been developed in a way concurrent, permitting better conditions of use in real time.Also, it is accomplished the definition of an architecture for the design of groupware applications and it is presented the implementation of a cooperative editor for multimedia documents in the one which is integrated the algorithm of concurrent control that it has been developed and defined in the present work.

From ACT-ONE to Miranda, a translation experiment

It is now almost universally acknowledged that the data language ACT-ONE associated with the formal description technique LOTOS is inappropriate for the purpose of OSI formal description. In response to this the LOTOS restandardisation activity plans to replace ACT-ONE with a functional language. Thus, compatibility between ACT-ONE and the replacement data language becomes an issue. In response to this, we present an experimental investigation of backward compatibility between ACT-ONE and the new LOTOS data language. Specifically, we investigate translating ACT-ONE data types into the functional language Miranda. Miranda has been chosen as it is a widely used functional programming language and it is close in form to the anticipated new data language. This work serves as a `verification of concept' for translating ACT-ONE to the E-LOTOS data language. It identifies the bounds on embedding ACT-ONE in a functional data language. In particular, it indicates what can be translated and what cannot be translated. In addition, the paper reveals pertinent issues which can inform the E-LOTOS work. For example, which constructs are needed in E-LOTOS in order to support the class of data type specifications typically made in the LOTOS setting? We conclude with a number of specific recommendations for the E-LOTOS data language.

A general-purpose multimedia synchronization mechanism based on causal relations

Designing distributed multimedia applications raises temporal and spatial synchronization issues related to processing, transport, storage, retrieval and presentation of data, sound, still images and video. Within this framework, the paper aims to define a general-purpose multimedia synchronization mechanism, known as the conditional delivery mechanism, capable of addressing both intraand inter-stream synchronization issues. The proposed mechanism, based on the identification of causal relations among information units of one or several streams, is designed to ensure that these causal relations, expressed at the user's level, are satisfied when delivering the streams. The conditional delivery mechanism is analyzed in depth and both informal and formal specifications of the mechanism are provided. The formal specification refers to an extension of the standard formal description technique LOTOS (RT-LOTOS for real-time LOTOS). Validation results of the conditional delivery mechanism are finally presented for a distance and interactive training application.

The RT-LOTOS formal specification of the conditional delivery mechanism

The paper deals with the formal specification of a general-purpose multimedia synchronization mechanism, known as the conditional delivery mechanism capable of addressing both intraand inter-stream synchronization issues. The proposed mechanism, initially introduced in [3, 11], is based on the identification of causal relations among information units of one or several streams and has the purpose of ensuring that these causal relations, expressed at the user's level, are satisfied when delivering the streams. The formal specification of the synchronization mechanism refers to an extension of the standard formal description technique LOTOS (RT-LOTOS for Real-Time LOTOS) which adds to LOTOS the capability of expressing several time-related features.

On the design of side-stick controllers in fly-by-wire aircraft

This paper presents the problem of designing the functional behaviour of the interaction between two side-stick controllers, an autopilot, and a flight control computer in a fly-by-wire aircraft. Two models are developed using the ISO formal description technique LOTOS, and analysed using rigorous abstract testing techniques.

VHDL generation from a timed extension of the formal description technique LOTOS within the FORMAT project

In this paper we present a translation from high-level specifications written in the formal description technique LOTOS to hardware descriptions in the standard language VHDL. The objective is to use the formal foundation of LOTOS in order to improve the design phase of hardware components. VHDL is used as an intermediate step, taking advantage of the existing simulation and synthesis tools. The translation methodology proposed in this paper has required the extension of LOTOS with timing features and will be supported by automatic tools, that are already under development.

Introducing structure into behavioural descriptions obtained from timing diagram specifications

Communication-dominated hardware is quite naturally specified in terms of timing diagrams. By providing timing diagrams with a formal semantics in terms of a timed extension of the formal description technique LOTOS, we obtain formalized pure behavioural specifications. Hereupon we apply correctness-preserving transformations, which are initiated by the user's directives and which iteratively lead to structural specifications. These can be further compiled, eg. into VHDL code.

LOEWE: A LOTOS engineering workbench

LOEWE is an integrated tools environment for the specification, analysis, and implementation of communication software. Although primarily based on the formal description technique LOTOS, LOEWE additionally offers multiple, semantically equivalent representations of a given protocol specification. Each format is specially adapted to support specific tool functionality: processes are used for simulation and compilation, fast state space exploration is performed on extended finite state machines, and labelled transition graphs are used for system verification. LOEWE currently contains a LOTOS syntax and static semantic verifier, a generator of extended finite state machines with associated interactive state exploration tools, a temporal logic verifier, a compiler to generate C code from LOTOS behavior expressions, a translator of LOTOS abstract data type operations to a set of LISP functions, and a graphical trace analyzer of LOTOS process interactions.

PTD: Architectural system description support based on visual specification languages

Formal languages become more and more necessary if we want to assure the satisfaction of the requirements of a system during its development. Several formal methods are gaining wider acceptance in spite of their difficulties to be applied in large systems design. The availability of graphical workstations, give us the possibility to create system specifications in a graphical way enhancing the intuition during this process. Visual languages formally related with formal description techniques, make possible to combine the advantages derived from mathematical models and graphical design. In this paper we present a formal visual language, named Process Topologie Diagrams (PTD), close to the formal description technique LOTOS. It is defined mathematically with a set of operators to manipulate PTDs. The language is supported by a software tool (editor, conversion from/to LOTOS, textual and graphical). There are also outlined methodological guidelines to support the architectural description of a system. This allow the generation of LOTOS specifications from a subclass of PTDs. The notation was applied to the specification of a gateway between the Digital Subscriber Signalling System No. 1 (DSS1) and the ISDN user part (ISUP) of Signalling System No. 7 (SS7). We plan to extend this visual formalism to support other kinds of system specifications and to enrich the model to deal with time requirements and PTDs animation.

Application of Formal Description Techniques to Real-Time Scheduling

Abstract In this paper we describe a study about the applicability of Formal Description Techniques like LOTOS to analyse and validate real-time subsystems. The Basic Priority Inheritance scheduling algorithm has been specified using the Formal Description Technique LOTOS. With the help of the specification, validation tests have been derived and applied to an independent VLSI implementation of the mentioned algorithm embedded in an Ada tasking co-processor. With this experience it has been shown that Formal Description Technique LOTOS can be applied to specify real-time subsystems and therefore to develop and validate them.

Introduction to LOTOS through a worked example

The practical application of formal description techniques (FDT) is becoming increasingly important in computing. However, there remains a gulf in the literature between the language of application developers and the more theoretical language often used to describe formal methods. The aim of this paper is to try to bridge this gap by introducing the formal description technique LOTOS in a non-theoretical manner. The main features of LOTOS are introduced through a worked example, a specification of a multi-way phone system. This example was chosen because the specification is compact and yet is sufficiently complex to introduce most LOTOS features. Furthermore, the protocols involved in a multi-way phone are intuitive. The paper also stresses the importance of supporting tools in the development of formal specifications and presents two tools, namely SEDOS and CAESAR/ALDÉBARAN, and explains why they are important in the specification process.

The derivation of conformance tests from LOTOS specifications

The derivation of conformance tests for communication protocols is discussed. Protocol specifications are considered in the formal description technique LOTOS, which has been developed by the International Standards Organization. Test processes which preserve the structure of the protocol specifications are constructed. Laws are presented for handling basic LOTOS operators. The test processes obtained by applying these laws are related to the theoretical notion of canonical testers. The conversion of the test processes into finite test suites is discussed. Their relationship to current practice in test suite design is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Formal modelling of telematic services using LOTOS

The paper describes modelling of a distributed real-time telecommunication system. It is assumed that the system handles integrated voice and data communication. The purpose of this note is formal description of telematic services that allows their modular decomposition. The formal description technique LOTOS is chosen for application of this idea.

LOTOS based derivation methodology in the PRODAT project

The article describes an experience on using the formal description technique LOTOS for developing a protocol architecture on a real time embedded multiprocessor systems. The product developed during the project is a satellite communications mobile terminal 1 to be installed on board of aircrafts, ships, or trucks. The objective of the experiment has been evaluating the impact of using formal languages for systems specification and design, in the software life cycle. The use of behaviour equivalences and hiding in LOTOS, as well as its precise semantical definition, give a powerful basis for analyzing the design of a system which clearly supersedes the normal approach to design analysis based on walk-throughs, inspections, reachability analysis, etc, … The main phases of the project development are analyzed, with emphasis on the influence of using LOTOS in the design cycle.