Formal Description Techniques Research Articles

Trends in formal description techniques

Trends in formal description techniques

Formal methods for broadband and multimedia systems

The proper capture of desired system properties is a pivotal step in providing high quality systems. The formal specification of these properties is necessary to provide unambiguous documentation as well as automated transformation of system requirements during all stages of the life cycle. The standardized Formal Description Techniques (FDTs) Estelle and SDL have proved useful for the specification of traditional protocols and distributed systems. With the availability of high-speed networks new applications with additional requirements and characteristics are becoming reality. These requirements are often referred to as Quality of Service (QoS) requirements. We show that the above-mentioned FDTs do not possess the expressiveness to capture important classes of QoS requirements, namely quantitative deterministic real-time-related properties. It is the purpose of this paper to exemplify steps that need to be taken in order to overcome this deficit. We first discuss choices that need to be made when designing a suitable real-time execution model for SDL and Estelle and proceed to present two remedies to the inexpressiveness problem: First, we introduce the concept of complementary real-time specification by reconciling the semantic models of Metric Temporal Logic and SDL and showing how both languages can be used in a complementary fashion. Second, we suggest a language extension and the corresponding semantic interpretation for Estelle. While we present examples from the domain of multimedia and broadband systems, the applicability of our specification methods extends to hard real-time systems. Finally, we discuss extensions of our techniques to capture QoS stochastic properties, and we allude to formal requirements verification and automatic implementation based on our techniques.

On measuring the complexity of an estelle specification

Software metrics are useful quantitative indicators to assess and predict software quality attributes; a commonly measured attribute is software complexity. The main drawbacks of these metrics are: they can only be calculated after a major development effort has been committed to producing the source codes; they cannot provide early feedback during the specification phase; and subsequently it is expensive to make changes to the system, if so indicated by the metrics. Formal Description Techniques (FDTs) enable formal specification to be systematically analyzed. They should also make it possible to assess software quality attributes like maintainability and reliability, and to predict the development or maintenance cost/effort early in the specification phase of the formal protocol development life cycle. To date, little work has been devoted to this area. In this paper, we describe how the complexity of an Estelle specification can be measured. The Sliding Window Protocol specified in Estelle is used as an example to illustrate our approach to measuring the complexity of an Estelle specification. The Management Decision Support System (MDSS), which integrates software measurement into the formal protocol development, is also described in this paper.

Formalizing GDMO Action and NotificationDefinitions — Results from a Case Study

One of the main problems in GDMO is the lack of adequate means to define the behavior of managed objects. This paper reports the experiences that have been gained in the GDMO project, a joint project of Deutsche Telekom AG and the Institute for Software Technology, with formalizing actions and notifications of a sample GDMO specification. It has been investigated how different formal description techniques (FDTs), namely an object-oriented Z dialect and SDL, may be used to describe the semantics of actions and notifications. However, the case study showed that an integration of FDTs into GDMO is technically difficult and not very likely to improve the overall quality of GDMO specifications.

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 Timed Rewriting Logic Semantics for SDL: A Case Study of the Alternating Bit Protocol

SDL is an industrial standard formal description technique for telecommunication systems. Despite its wide spread use and industrial importance it lacks at present an adequate formal semantics integrating its static, dynamic, and real-time aspects. Timed Rewriting Logic (TRL) is a new variant of Rewriting Logic, an algebraic formalism which allows the dynamic behaviour of systems to be axiomatised using rewrite rules. In TRL rewrite rules can be labelled with time constraints and this provides a means of reasoning about time elapse in real-time systems. TRL has been used to develop an object-oriented specification language Timed Maude for distributed real-time systems. In this paper we demonstrate the expressive power and versatility of Timed Maude by applying it to the definition of a formal semantics for SDL. The semantics we develop captures in an intuitive way the hierarchical structure of SDL specifications and integrates within one formalism the static and dynamic aspects of an SDL system. We demonstrate and motivate the semantics we develop by considering in detail a case study of the bench mark alternating bit protocol.It is a pleasure to thank U. Hinkel, K. Meinke and M. Wirsing for their helpful comments and advice during the preparation of this paper. We also gratefully acknowledge the financial support of the British Council and DAAD which has made this collaborative work possible.

Automated Test Generation from Specifications Based on Formal Description Techniques

This paper describes a research result on automatic generation of abstract test cases from formal specifications by applying many related algorithms and techniques such as the testing framework, rural Chinese postman tour and unique input output sequence concepts. In addition, an efficient algorithm for verifying the strong connectivity of the reference finite state machine and the concept of unique event sequence are explained. We made use of several techniques to form an integrated framework for abstract test case generation from LOTOS and SDL specifications. A prototype of the proposed framework has been built with special attention to real protocol in order to generate the executable test cases in an automatic way. The abstract test cases in tree and tabular combined notation (TTCN) language will be applied to the TTCN compiler in order to obtain the executable test cases which are relevant to the industrial application.

An ODP computational model of a cooperative binding object

A next generation of systems that should appear will have to manage simultaneously several geographically distributed users. These systems belong to the class of computer-supported cooperative work systems (CSCW). The development of such complex systems requires rigorous development methods and flexible open architectures. Open distributed processing (ODP) is a standardization effort that aims at providing such architectures. ODP features appropriate abstraction levels and a clear articulation between requirements, programming and infrastructure support. ODP advocates the use of formal methods for the specification of systems and components. The computational model, an object-based model, one of the abstraction levels identified within ODP, plays a central role in the global architecture. In this model, basic objects can be composed with communication and distribution abstractions (called binding objects) to form a computational specification of distributed systems, or applications. Computational specifications can then be mapped (in a mechanism akin to compilation) onto an engineering solution. We use an ODP-inspired method to computationally specify a cooperative system. We start from a general purpose component that we progressively refine into a collection of basic and binding objects. We focus on two issues of a co-authoring application, namely, dynamic reconfiguration and multiview synchronization. We discuss solutions for these issues and formalize them using the MT-LOTOS specification language that is currently studied in the ISO standardization formal description techniques group.

Formal description and verification of Hybrid Rule/Frame-based Expert Systems

A Hybrid Expert System combines multiple representation paradigms into a single integrated environment for modeling and reasoning of complicated real world phenomena. For a Rule- and Frame-based integration, it models the problem domain using the concepts of Classes and Rules together. If Domain knowledge (concepts) is related by production rules and frame hierarchy, then anomalies may arise among this knowledge (concepts) due to the existence of two mutually independent formalism of relations. A contribution is made in this paper to developing formal description techniques for the detection of anomalies attributed to the integration of production rules with the inheritance of object properties within the object hierarchy. The main idea is to convert the HES into a State Controlled Coloured Petri Net (SCCPN) where the object hierarchy, property inheritance and production rules are modelled as separated components in the same SCCPN. The detection and analysis of the anomalies (i.e. Correctness, Consistency and Completeness) in the system are done by constructing and examining the reachability tree spanned by the knowledge inference.

From Estelle to Erlang

Formal Description Techniques, like Estelle, are being used for the specifications of telecommunication protocols. While many telecommunication software manufacturers are still using programming languages that were developed in the late 1960s or 1970s, Ericson's Computer Science Laboratory in Sweden has developed a new declarative programming language, called Erlang, which supports concurrency, distribution, error handling and code updating. This article first describes how Estelle specifications can be translated into Erlang codes, then presents its application to the Alternating Bit protocol, and finally draws a comparison between this and the compilation method for automatic communication protocol implementation. The motivation behind this work comes from the need of having a better understanding between Erlang, being a very young declarative language and suited to implementing communication protocols due to the features that were built into it, and the FDT, Estelle, in order to obtain more benefits from these languages when implementing communication protocols.

Applying the architectural semantics of ODP to develop a trader specification

This paper provides an introduction to the role of Formal Description Techniques in the development of an architectural semantics for Open Distributed Processing (ODP). Following a brief overview of ODP and the Reference Model for ODP, an outline of the reasons for developing an architectural semantics is given. The different approaches currently being taken for an ODP architectural semantics are presented. Finally, an ODP infrastructure component - the ODP Trader - is specified using the architectural semantics work, and the advantages gained from the approach are discussed.

An experience in using EDT to process the ISO transaction processing estelle specification

One of the hindrances to the adoption of the uses of Formal Description Techniques (FDTs) in the computer and communications industries is the nonavailability of standardized formal specification of protocol. The Transaction Processing (TP) Draft International Standard (DIS) published in 1990 was probably the first protocol that has been specified both in LOTOS and Estelle by ISO. The Estelle specification was big in size with about 8000 lines of codes. However, even with the availability of this standardized formal specification, its usefulness is limited unless there is a computer tool that supports its use for protocol development. This article describes the experience in using the Estelle Development Toolset (EDT) to compile, to generate C codes from, and to simulate the TP DIS Estelle specification. It aims to provide developers with some pointers to the potential difficulties and successes of protocol development of an ISO standardized formal specification using a computer tool. One of the ways to help industrialize the uses of FDTs is by having more reports on uses of standardized formal specifications. With the lessons learned from this work, this article also attempts to encourage wider industrial uses of FDTs and standardized formal specification for protocol development.

An estelle-based incremental protocol design system

Formal description techniques (FDTs) provide formal and abstract ways to specify what protocols have to do and what features protocols need. Estelle is an FDT defined by the International Organization for Standardization for protocol specifications. We present an incremental protocol design system that contains an incremental protocol verification technique and an Estelle translator. Our incremental protocol design system allows on-line reverification after respecification. That is, instead of verifying respecified (modified) protocols from scratch, the reverification procedure is executed continuously and incrementally at the modification point. Using the translator, Estelle protocol specifications can be translated and interpreted for protocol verification. To meet the requirement of modifying protocol specifications written in Estelle at run time, the Estelle translator allows incremental translation and interpretation of the modified Estelle specification part for incremental verification. To further reduce the number of global states to be explored, the concept of dead and live variables is incorporated into our incremental verification technique. Based on the incremental verification technique and the Estelle translator, an incremental protocol design system (IPDS) is developed on SUN SPARC OPENLOOK work-stations. Using IPDS, protocol designers can analyze the verification results, interactively modify the protocols, and then continue the verification incrementally.

A success story of verifying a real complex protocol

The advance in protocol specification using Formal Description Techniques (FDTs) in recent years has opened up a new horizon for protocol development. Techniques for verifying communication protocols have progressed significantly in the past decade. These developments have long promised to make contributions to the development of protocols. However, they are seldom adopted by the industry and applied by academia to real applications of considerable size. Reports on the successes of verifying real complex protocols have been rare; and it is by the suitability of their industrial applications and the extent of their usage that FDTs will ultimately be judged. This article presents the success story of using an automated stool, PROTEAN, for verifying a real complex protocol, the ISO FTAM protocol. The formal specifications are first discussed, followed by the description of how the specifications are verified by PROTEAN, and finally, the verification results are reported. The merit of this article is the demonstration of how formal specification and protocol verification can be used to improve a real protocol. It aims to encourage more research devoted to real applications and also to make a case for increased industrial attention and support for formal method approach to protocol development.

Petri nets for protocol engineering

This paper presents a review of the role Petri nets play in protocol engineering. This methodology provides various models for specification and many methods for verification and other software engineering tasks concerning protocols. In particular, many property-preserving transformations and compositional methods are available for reducing the impact of state explosion on the two well-known verification approaches — reachability analysis and invariant analysis. By conversion, Petri nets can be used for studying systems specified by many of the formal description techniques frequently used for protocol investigation such as MSC, SDL, ESTELLE, LOTOS, CCS, CSP and CCSP. For example, Petri nets can be used for deriving test sequences and cyclomatic complexity measure for LOTOS. Also, many equivalence relations concerning the theoretical foundation of protocol engineering have been formulated on the basis of Petri nets. Other developments of Petri nets related to protocols include: Petri nets with temporal logic, feature interaction, synthesis, complexity measure, timed or object-related Petri nets, etc.

Formal Codesign Methodology with Multistep Partitioning

A codesign methodology is proposed which is suitable for control‐dominated systems but can also be extended to more complex ones. Its main purpose is to optimize the trade‐off between hardware performance and software reprogrammability and reconfigurability. The methodology proposed intends to cover the development of the whole system. It deals in greater detail with the steps that can be made without the need for any particular assumption regarding the target architecture. These steps concern splitting up the specification of the system into a set of individually synthesizable elements, and then grouping them for the subsequent mapping stage. In order to decrease the complexity of each partitioning attempt, a two step algorithm is proposed, thus permitting a wide exploration of possible solutions. The methodology is based on the TTL language, an extension of the T‐LOTOS Formal Description Technique which provides a large amount of operators as well as a formal basis. Finally, an example pointing out the complete design cycle, excepting the allocation stage is provided.

An Estelle translator for incremental protocol verification

Abstract Formal Description Techniques (FDTs) provide formal support for each phase of protocol development. Estelle is one of the FDTs proposed by the International Organization for Standardization (ISO) to formally specify distributed systems, especially for communication protocols. In this paper, we present the development of an Estelle translator which allows protocol designers to interactively add/delete transitions at the run time of protocol verification. The Estelle translator can translate Estelle‐specified protocols into the internal extended finite state machine tables, which have corresponding information of each protocol entity. The main feature of the Estelle translator is its capacity to support incremental protocol verification. The incremental translating components in our Estelle translator allow protocol designers to modify protocols at the run time and continue the verification at the modification point incrementally. That is, our Estelle translator allows protocol designers interactiv...

A new approach to ADT specification support based on reuse of similar ADT by the application of Case-Based Reasoning

Abstract Data Type (ADT) is a powerful tool having a very good mathematic basis called many-sorted algebra and is also combined into several Formal Description Techniques (FDTs). By using ADT, a protocol or a software system can be specified in a very abstract way. It also facilitates the verification and validation of the specified system. However, in practice ADT is rarely used because it is difficult for a non-ADT expert to specify. As a consequence of this, in order to promote the widespread use of ADT and FDT, a support method for ADT specification is necessary. Unfortunately, there is almost no such a support method so far. We propose an ADT specification support method in terms of support system based on Case-Based Reasoning (CBR) which is a kind of problem solving by reusing solutions of the existing similar problem with some appropriate modifications. CBR has been used in some researches. But there is no research which uses this technique for ADT specification support so far. The support system can ease the specification of ADT and prevent the user from spending too much time and effort in specifying the whole ADT from the beginning. Our support system consists of four parts: (1) Case base of ADTs; (2) Requirement Acquisition Template; (3) Search mechanism for finding the most similar case in (1); (4) Modifier for modifying the retrieved case to meet the requirement of user. Among these parts, the core of the support system is the search mechanism which is based on the definition of similarity of ADTs. In this paper, we first propose an ADT specification model which defines a data carrier part of an ADT as a combination of constructors of four patterns. Based on the specification model, a similarity definition is given. Furthermore, we have designed the support system. Finally, in order to evaluate the effectiveness of the system, we experimented with data types of service and protocol in the data communication field. From the evaluation, the effectiveness of the system is ensured.

Cross-viewpoint consistency in open distributed processing

The paper discusses the use of viewpoints in the ODP (Open Distributed Processing) standardisation initiative. The ODP reference model is a new framework, going beyond OSI (Open Systems Interconnection). Multiple viewpoints are used to specify complex ODP systems. Consistency of viewpoint specifications is clearly a central issue. In addition, formal techniques have an increasingly significant role within ODP, and so mechanisms are needed that support consistency checking of formal specifications. An overview is provided of the ODP reference model and the use of viewpoints within it, before discussing consistency within ODP and how it can be realised using formal notations. Consistency checking is illustrated using the LOTOS formal description technique.

Adding rigour to object-oriented analysis

The rigorous object-oriented analysis (ROOA) method integrates formal description techniques with standard object-oriented analysis methods. ROOA provides a systematic development process which, starting from a set of informal requirements, produces an executable objected-oriented analysis model. The model is expressed in LOTOS and provides a precise and unambiguous formal requirements specification of the static, dynamic and functional aspects of a problem. As the specification is executable, prototyping can be used to validate the specification against the requirements. Inconsistencies, omissions and ambiguities in the requirements can be detected sufficiently early in a development so that feedback can be given to the requirement capture process.