Formal Requirements Specification Research Articles

Validation-directed specification of communications systems

Considerable interest has recently developed in industry in the concepts of life-cycle testing and concurrent engineering. A key component in these concepts is advance planning and preparation for validation activities (primarily testing and verification activities). In this paper, we introduce a new, testability-directed specification method, namely ETAL (Extended Trace Assertion Language) with relative clocks. This method extends and applies work by Parnas on formal specification of software requirements by trace assertions and work by Lamport on logical clocks in distributed systems. As a result, we derive a practical model for specifying and analysing global events with a view towards verification and testing. We give an example of the application of this approach to derive a testability-directed specification of a communications service provider, and illustrate how the approach facilitates conformance test results analysis.

Validating timing requirements for time basic net specifications

This article deals with the validation of formal requirement specifications of real-time systems. Formally specified requirements can be validated by both direct execution and by proving properties at the specification level. We first discuss how the timing characteristics of a system can be specified by a formalism based on high-level Petri nets. Then we show how its temporal properties can be proven by means of a symbolic execution-based proof method for time reachability analysis. Depending on the complexity of the model of the specified system, the method may contain some undecidable steps and require interaction with the user. In many practical cases, however, the method can be performed mechanically and has acceptable response times.

Response to “the formal specification of safety requirements for storing explosives”

Abstract This short communication is a response to [MuS93] investigating their ACS system specification. The main point in this paper is that executing specifications can be used as a feasible way of validating them. It is essential to have tool support which enables one to write a generally not executable specification, and then prototype (parts of) it directly in the specification language, without translating it into some other prototyping language.

Requirements specification for process-control systems

The paper describes an approach to writing requirements specifications for process-control systems, a specification language that supports this approach, and an example application of the approach and the language on an industrial aircraft collision avoidance system (TCAS II). The example specification demonstrates: the practicality of writing a formal requirements specification for a complex, process-control system; and the feasibility of building a formal model of a system using a specification language that is readable and reviewable by application experts who are not computer scientists or mathematicians. Some lessons learned in the process of this work, which are applicable both to forward and reverse engineering, are also presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The formal specification of safety requirements for storing explosives

Abstract In this paper we consider the current practices involved in the storage of explosive articles and substances. In the spirit of Defence standard 00-55, we formalize the safety requirements of the ACS software which is used to manage certain MOD holdings in the United Kingdom using the specification language VDM. We also prove some properties of these safety requirements and comment on a similar OBJ3 specification.

A formal requirements specification method based on data flow analysis

As formal methods are increasingly used in the development of industrial-scale software systems, there is a growing awareness of the need to integrate formal notations with existing structured software development methods. To make requirements analysis both comprehensible and rigorous, a formal requirements specification method is proposed that combines and extends DeMarco data flow diagrams with the Vienna development method. The specifications produced using this method have good readability, a wellde signed structuring mechanism, and precise semantics. This article details work toward development of a verified analysis approach based on the concept of consistency checking for guaranteeing the correctness of analysis steps.

A hybrid knowledge representation as a basis of requirement specification and specification analysis

A formal requirement specification language, the frame-and-rule oriented requirement specification language FRORL, developed to facilitate the specification, analysis, and development of a software system is presented. The surface syntax of FRORL is based on the concepts of frames and production rules that may bear hierarchical relationships to each other, relying on multiple inheritance. To provide thorough semantic foundations, FRORL is based on a nonmonotonic variant of Horn-clause logic. Using the machinery of Horn-clause logic, various properties of a FRORL specification can be analyzed. Among the external properties of FRORL are formality, object-orientedness, and a wide spectrum of life cycle phases. Intrinsic properties are modularity, provision for incremental development, inheritance, refinement, reusability, prototyping, and executability. A software development environment based on FRORL has been implemented using the C language on a Sun workstation. >

Software development: two approaches to animation of Z specifications using prolog

Formal methods rely on the correctness of the formal requirements specification, but this correctness cannot be proved. This paper discusses the use of software tools to assist in the validation of formal specifications and advocates a system by which Z specifications may be animated as Prolog programs. Two Z/Prolog translation strategies are explored; formal program synthesis and structure simulation. The paper explains why the former proved to be unsuccessful and describes the techniques developed for implementing the latter approach, with the aid of case studies.

Fault-Tolerance in Real-Time Systems

Abstract With ever-increasing reliance on digital computers in embedded systems such as in space, avionics, manufacturing, and life-support monitoring/control applications, the need for dependable systems that deliver services in a timely manner has become crucial. Embedded systems often interact with the external environment and operate under strict timeliness and reliability requirements. Fault tolerance and real-time requirements on a system often influence one another in subtle ways, for example, the requirements on a highly—available system, such as an air traffic control system, may derive the timing constraints imposed on certain critical tasks. In cases where a set of interacting tasks operate under strict timing constraints, missing a deadline may result in a catastrophic system failure, which was termed a dynamic failure in (Shin, Krishna, and Lee, 1985). This paper argues that fault- tolerance and real-time requirements are not orthogonal and it addresses some of the challenges that confront the designers of fault-tolerant real-time systems. These challenges include formal specification of reliability and timing requirements, appropriate language and operating system support for providing fault-tolerance in a time-critical system, new scheduling theories which consider multiple resources and fault-tolerance, tradeoff between time and space redundancy, and predictable redundancy management in the presence of faults.

Informal and formal requirements specification languages: bridging the gap

The differences between informal and formal requirements specification languages are noted, and the issue of bridging the gap between them is discussed. Using structured analysis (SA) and the Vienna development method (VDM) as surrogates for informal and formal languages, respectively, two approaches are presented for integrating the two. The first approach uses the SA model of a system to guide the analyst's understanding of the system and the development of the VDM specifications. The second approach proposes a rule-based method for generating VDM specifications from a set of corresponding SA specifications. The two approaches are illustrated through a simplified payroll system case. The issues that emerge from the use of the two approaches are reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Specification and design of shared resource arbitration

The specification, modular design and verification of distributed communicating systems is demonstrated by an example. The scheduling of the access to a common shared resource by a finite number of devices with priorities is a well known problem from hardware and operating systems design. Using the concepts of stream processing continuous function a variety of formal requirement and design specifications for this problem are given and the design specifications are proven correct w.r.t the requirement specifications. From the design specifications one can immediately read off applicative programs implementing the requirement specifications. Special attention is paid to the aspect of modelling time.

Proving properties of a safety-critical system

The paper describes the FOREST approach to formal requirements specification and particularly the role of an automated theorem prover in validating specifications written in MAL, the FOREST logic. The MAL prover uses a tableau method for constructing its proofs, with rules to handle the action modalities and quantification of MAL. The authors illustrate its use in validation by using the prover to establish that a safety-critical railway-signalling specification has some desirable safety properties.< >

Formal specification of geographic data processing requirements

A formal foundation for the specification of geographic data processing (GDP) requirements is established. Emphasis is on modeling data and knowledge requirements rather than processing needs. A subset of first-order logic is proposed as the principal means for constructing formalizations of the GDP requirements in a manner that is independent of the data representation. Requirements executability is achieved by selecting a subset of logic, compatible with the inference mechanisms available in Prolog. Concepts with GDP significance such as time, space, and accuracy are added for the formalization without losing Prolog implementability or separation of concerns. Rules of reasoning about time, space, and accuracy can be compactly stated in a subset of second-order predicate calculus and can be easily modified to meet the particular needs of a specific application. The feasibility of the approach is established with the aid of a prototype implementation of the formalism in Prolog. The implementation also provides the means for the graphical rendering of logical information on a high-resolution color display. >

Formal specification of real time systems

The paper discusses general issues related to formal requirements specification of real time embedded systems. It characterizes the distinguishing features of embedded systems and then presents the role of requirements specifications and emphasises the need for their formality. The formal specifications are considered from the system analyst perspective. It is argued that functionality, parallelism and timing are the relevant aspects of requirements of embedded systems. The basic semantic concepts related to formal specification of those aspects are briefly reviewed and evaluated. It is demonstrated how a global state model can be developed to specify requirements for a simple example system using the temporal logic (property-oriented) and Petri net (state transition-oriented) approaches. Brief characteristic of some distributed state models is also included.

A specification framework for software processes: formal specification and derivation of information base requirements

A specification framework for software processes: formal specification and derivation of information base requirements

DOMINIE: A DOMAIN INDEPENDENT INSTRUCTIONAL ENVIRONMENT FOR COMPUTER-BASED PROCEDURAL SKILLS (ESPRIT Project 1613)

There are many logistical and tutorial reasons for developing Intelligent Tutoring Systems (ITSs). The increasing presence of inherently complex, evolving systems requires cost-effective methods of producing tutorial material. Furthermore, it is generally accepted that training opportunity problems can be resolved by flexible tutorial mechanisms and that artifical intelligence technology can enable knowledge representation for complex procedures. Other advantages include the ability to explicity represent the expertise of the human teacher and achieving individualised, non-threatening tuition.In response to Alcatel's major training need for complex computer-based procedures, the Engineering Support Centre developed a micro based prototype ITS shell. Issues considered during ITS development included: selecting an appropriate formal requirements specification technique which ensures precision, communicability, implementability and assistance with reasoning for design; and simulation of the target system to enable the student to gain on-line experience. The formal specification technique currently being evaluated is Modal Action Logic, and the ITS shell employs facsimile simulation without the necessity of the presence of the target software package during tuition.Within the ESPRIT project the prototype ITS has been used as a test-bed for the development of a pre-product, field tested domain independent instructional environment (Dominie). Field trials have been performed in the application areas of office automation package tailoring (in Italian) and telephone exchange maintenance (in English). The results have assisted re-specifying the prototype, primarily in terms of its control stucture, knowledge representation method, tutorial and assessment strategies and student modelling technique.Future work within year one of the ESPRIT project will involve the first implementation of Dominie and the specification and implementation of a trainer interface. Year two will include further field trials and will involve a greater number of application areas. These trials will enable evaluating Dominie's tutorial effectiveness and organisational impact prior to refining the system.

Formal requirements specification of process control systems

The increasing size of software systems requires methods and tools for their development . Currently only a few tools are practically used. This paper presents a system which was developed in order to support requirements specification of process control systems. The paper introduces a formal language and describes, how the system supports the steps from ideas to a formal requirements specification.

How should applications be developed?

In his text, Application Development without Pro grammers, James Martin argues that many of the problems of traditional systems development, including long development cycles, formal requirements specification, and formal maintenance procedures, can be overcome by providing users with the tools to develop their own applications. In the environment Martin describes, users will use report and application generators to make queries and to generate reports from existing databases. Working with systems analysts, users will also create prototypes of systems they need. (Martin, 1982, p. 55).

Enhancing FDM for the expression of concurrency requirements

This paper describes extensions to SDC's Formal Development Methodology that support formal specification and verification of concurrent system requirements. It outlines antecedents from first-order temporal predicate logic for these extensions and how they will be implemented.

Formal specification of information systems requirements

An organizational information system can be viewed, in a broad sense, as a computational model of organizational activity and function. Logical requirements of information systems are defined, according to this view, as constraints imposed by the logical structure of such a computational model on the design, implementation and operation of information systems. In this study a formal model for the specification of logical requirements is presented in detail and its role as a tool for systems development is discussed. Three main advantages of the specification of logical requirements that can be capitalized through the use of this formalism are: (1) logical requirements are invariant with respect to specific means in which information processing is actually accomplished; (2) they can be easily related to relevant aspects of organizational activity and function; and (3) they can be related to basic components of the corresponding software systems, either existing or being developed.