Specification Of Real-time Systems Research Articles

Absolute versus Relative Time in Process Algebras

Timed process algebras are useful tools for the specification and verification of real-time systems. We study the relationships between two of these algebras, c I pa (closed interval process Algebra) and TCCS (temporal CCS ), which deal with temporal aspects of concurrent systems by following very different interpretations: durational actions versus durationless actions, absolute time versus relative time, timed functional behavior versus time and functional behavior, local clocks versus global clocks. We show that these different choices are not irreconcilable by presenting simple mappings from c I pa to TCCS which preserve the behavioral equivalences over the two timed calculi. These results hold whenever basic actions are interpreted as either eager or lazy, whenever the starting time of action execution is observed rather than their completion time. A study on the size of the labelled transition systems describing the transitional semantics of cIpa processes and those describing the transitional semantics of their translated versions is also presented.

Real-Time Maude: A Tool for Simulating and Analyzing Real-Time and Hybrid Systems

Rewriting logic can be used to specify a wide range of real-time and hybrid systems under a variety of time models, including discrete and dense time models. The Real-Time Maude tool, built on top of the Maude rewriting logic language, supports specification of real-time and hybrid systems in timed modules and timed object-oriented modules, which are transformed into equivalent Maude modules. The tool then supports execution of such specifications in several rewrite modes, corresponding to different criteria for advancing time. Besides system simulation by default execution in a given rewrite mode, the tool has a library of execution strategies and commands that can search all the possible computations from an initial state, within given rewrite mode and search bounds, to partially model check desired properties, including properties expressible in a class of linear time timed temporal logic formulas. The paper discusses the tool's theoretical basis, its specification language, and its library of evaluation and search strategies. The user can add new formal analysis strategies to the library, as illustrated by a scheduling case study. We also summarize our experience with applications and our future plans.

Reachability analysis of real-time systems using time Petri nets

Time Petri nets (TPNs) are a popular Petri net model for specification and verification of real-time systems. A fundamental and most widely applied method for analyzing Petri nets is reachability analysis. The existing technique for reachability analysis of TPNs, however, is not suitable for timing property verification because one cannot derive end-to-end delay in task execution, an important issue for time-critical systems, from the reachability tree constructed using the technique. In this paper, we present a new reachability based analysis technique for TPNs for timing property analysis and verification that effectively addresses the problem. Our technique is based on a concept called clock-stamped state class (CS-class). With the reachability tree generated based on CS-classes, we can directly compute the end-to-end time delay in task execution. Moreover, a CS-class can be uniquely mapped to a traditional state class based on which the conventional reachability tree is constructed. Therefore, our CS-class-based analysis technique is more general than the existing technique. We show how to apply this technique to timing property verification of the TPN model of a command and control (C2) system.

Expressive Completeness of Duration Calculus

This paper compares the expressive power of first-order monadic logic of order, a fundamental formalism in mathematical logic and the theory of computation, with that of the propositional version of duration calculus (PDC), a formalism for the specification of real-time systems. Our results show that the propositional duration calculus is expressively complete for first-order monadic logic of order. Our semantics for PDC conservatively extends the standard semantics to all positive (including infinite) length intervals. Hence, in view of the expressive completeness, liveness properties can be specified in PDC. This observation refutes a widely believed misconception that the duration calculus cannot specify liveness properties.

Experiences of using formal methods for chemical process control specification

This paper discusses the benefits of adding formal specification in B to existing controller synthesis techniques, and some of the limitations of B for this area of application. Examples from case studies carried out in the “Object-oriented specification of real-time and reactive systems” (ROOS) project are given.

Real-time Analysis of an IC Wire-bonding Inspection System

Though the need to consider all aspects of real-time in the development of a system is not new to control engineers, they are relatively new to the machine vision specialists, especially as they tend to come from various different backgrounds. In practice most vision experts tend to “tweak” their systems to match the speed of the application environment. They rarely use any formal or indeed informal methods to understand, design and analyse the real-time behavior of their systems. This paper, however, suggests that this trend needs to be reversed, and that correct timing of an operation is as important as correct logical operation. The paper starts by justifying the need to analyse the dynamic behavior of machine-vision systems. The paper then briefly reviews some of the basic concepts of real-time systems, and explores a tool available for the specification and analysis of real-time systems. Finally, the paper discusses the analysis of the real-time behavior of a machine vision system developed for the inspection of the bonding process occurring in IC fabrication.

ADDING FORM TO REAL-TIME SYSTEM SPECIFICATION AND SIMULATION

Specification and validation of a real-time system are often based on making simplistic predictions and assumptions about relevant behavior of the external environment and the controlled device interacting with it. However, in many cases, real-time systems physically interact with other external objects in a complex manner in a dynamically changing world and thus, their form (e.g. physical properties such as shape, mass, material, and configuration) can play a critical role in producing a correct specification and obtaining realistic simulation output. We present ASADAL/PROTO, a specification and simulation tool for real-time systems, that takes form into account in addition to the function and behavior handled by ASADAL/SIM, its predecessor. Simulation of the control system specification runs in conjunction with the environmental simulation, and the resulting interactive behavior of the controlled system is observed visually for analysis. Our vision is to incrementally model, simulate and analyze all three views (behavior, function, and form) of real-time system specification for its increased level of confidence at early prototyping stage.

Mapping and scheduling for heterogeneous architectures

Extensive and computationally complex signal processing and control applications are commonly constructed from small computational blocks where the load decomposition and balance may not be easily achieved. This requires the development of mapping and scheduling strategies based on application to processor matching. In this context several application algorithms are utilised and investigated in this work within the development framework (DF) approach. The DF approach supports the specification, design and implementation of real-time control systems. It also contains several mapping and scheduling tools to improve the performance of systems as well as tools for code generation. To improve the performance of an application, a new approach, namely the priority-based genetic algorithm (PBGA), is developed and reported in this article. The approach is applied to several applications using parallel and distributed heterogeneous architectures and its performance verified in comparison to several previously developed strategies.

An Object-Oriented Approach to Task-Graph Representation

Task graphs have been used for the specification and analysis of real-time systems for some time. We are currently developing a mobile code management system which uses a task-graph representation for specification, analysis, scheduling, dispatch, and resource allocation decisions. In this paper, we describe our limited hierarchical task-graph model, paying particular attention to its object-oriented representation in the Java language.

H-Astral and Its Use in the Development of Real-Time Control Systems

An important issue in the design and implementation of real-time control software is the verification of (time continuous) properties during system development such that even in early stages of the development adequate feedback on design decisions can be given. It is beyond any doubt that formal methods play an important role in this kind of verification. Our research of the past few years focused on applying formalisms in requirements specification and in developing tools for modeling, design and verification of specifications for real-time systems. The development approach builds upon requirements specifications constructed using the formal real-time specification language Astral. In this paper we discuss issues in the use of Astral in development and verification of real-time control systems and give an example of its use.

Specification and analysis of real-time systems with PARAGON

This paper describes a methodology for the specification and analysis of distributed realdtime systems using the toolset called PARAGON. PARAGON is based on the Communicating Shared Resources paradigm, which allows a realdtime system to be modeled as a set of communicating processes that compete for shared resources. PARAGON supports both visual and textual languages for describing realdtime systems. It offers automatic analysis based on state space exploration as well as userddirected simulation. Our experience with using PARAGON in several case studies resulted in a methodology that includes design patterns and abstraction heuristics, as well as an overall process. This paper briefly overviews the communicating shared resource paradigm and its toolset PARAGON, including the textual and visual specification languages. The paper then describes our methodology with special emphasis on heuristics that can be used in PARAGON to reduce the state space. To illustrate the methodology, we use examples from a realdlife system case study.

Guidelines for specifying automatic vehicle location and real-time passenger information systems using current best practice

Several bus companies and local authorities are showing a great deal of interest in automatic vehicle location (AVL) technology since AVL data can be used to drive systems which provide real-time passenger information at bus stops (which are perceived to be a potential source of increasing patronage and also have a high on-street profile). However, many AVL and real-time passenger information systems have been bought 'off-the-shelf' without consideration as to whether the system could be better with re-specification. To combat this problem, a comparison of the advantages and disadvantages of the various AVL technologies has been made to produce guidelines for the specification of AVL systems and real-time passenger information systems, and the results have been presented here. To identify current best practice, interviews were carried out with project managers of most of the real-time passenger information systems operational in the UK and some bus operators who were implementing AVL systems. The results suggest that no one system embraces all best practice and so there is potential to improve on the 'off-the-shelf' systems currently available from manufacturers.

Procedure-Level Verification of Real-time Concurrent Systems

We want to develop verification techniques for real-time concurrent system specifications with high-level behavior structures. This work identifies two common engineering guidelines respected in the development of real-world software projects, structured programming and local autonomy in concurrent systems, and experiments with special verification algorithm based on those engineering wisdoms. The algorithm we have adopted respects the integrity of program structures, treats each procedure as an entity instead of as a group of statements, allows local state space search to exploit the local autonomy in concurrent systems without calculating the Cartesian products of local state spaces, and derives from each procedure declaration characteristic information which can be utilized in the verification process anywhere the procedure is invoked. We have endeavored to implement our idea, test it against an abstract extension of a real-world protocol in a mobile communication environment, and report the data.

Life-cycle of a dual object-oriented specification model for real-time systems

Dual approaches for real-time systems specification try to integrate in a unique model/language the most interesting features of both operational and denotational approaches. In some cases, the object-oriented paradigm has been used for integrating the above aspects and as a support for covering with a uniform approach the development life-cycle from requirements analysis to application coding, by presenting initially a mainly denotational semantics which changes in operational semantics with the increase of implementation details. For these reasons, traditional development life-cycles are unsuitable, and more specific phases are needed to exploit the potentiality of the approach. In this paper, the authors present the life-cycle defined for a dual approach proposed in the literature—i.e., TOOMS/TROL.

Logical specification of reactive and real-time systems

Logical specification of reactive and real-time systems

A Graphical Language for Specifying and Analyzing Real-Time Systems

We present Graphical Communicating Shared Resources (GCSR), a formal language for the specification and analysis of real-time systems, including their functional, temporal and resource requirements. GCSR supports the explicit representation of system

Incremental Verification of Architecture Specification Language for Real-Time Systems

The concept of software architecture has recently emerged as a new way to improve our ability to effectively construct large scale software systems. However, there is no formal architecture specification language available to model and analyze temporal properties of complex real-time systems. In this paper, an object-oriented logic-based architecture specification language for real-time systems is discussed. Representation of the temporal properties and timing constraints, and their integration with the language to model real-time concurrent systems is given. Architecture based specification languages enable the construction of large system architectures and provide a means of testing and validation. In general, checking the timing constraints of real-time systems is done by applying model checking to the constraint expressed as a formula in temporal logic. The complexity of such a formal method depends on the size of the representation of the system. It is possible that this size could increase exponentially when the system consists of several concurrently executing real-time processes. This means that the complexity of the algorithm will be exponential in the number of processes of the system and thus the size of the system becomes a limiting factor. Such a problem has been defined in the literature as "state explosion problem". We propose a method of incremental verification of architectural specifications for real-time systems. The method has a lower complexity in a sense that it does not work on the whole state space, but only on a subset of it that is relevant to the property to be verified.

An Operational Semantics and Compiler for Real-Time Specifications1

The Modechart specification language is a formalism for the specification and implementation of real-time systems. This paper presents the semantics for Modechart in an operational style and a compiler for automatically synthesizing specifications. M

Experiences of Using Formal Methods for Chemical Process Control Specification

This paper discusses the benefits of adding fonnal specification in B to existing controller synthesis techniques, and some of the limitations of B for this area of application. Examples from case studies carried out in the “Object-oriented specification of Real-time and Reactive Systems” (ROOS) project are given

A Process Algebraic Approach to the Schedulability Analysisof Real-Time Systems

To engineer reliable real-time systems, it is desirable to detect timing anomalies early in the development process. However, there is little work addressing the problem of accurately predicting timing properties of real-time systems before implementations are developed. This paper describes an approach to the specification and schedulability analysis of real-time systems based on the timed process algebra ACSR-VP, which is an extension of ACSR with value-passing communication and dynamic priorities. Combined with the existing features of ACSR for representing time, synchronization and resource requirements, ACSR-VP is capable of specifying a variety of real-time systems with different scheduling disciplines in a modular fashion. Moreover, we can use VERSA, a toolkit we have developed for ACSR, to perform schedulability analysis on real-time systems specified in ACSR-VP automatically by checking for a certain bisimulation relation.