Real-time Temporal Logic Research Articles

Analyzing partially-implemented real-time systems

Most analysis methods for real-time systems assume that all the components of the system are at roughly the same stage of development and can be expressed in a single notation, such as a specification or programming language. There are, however, many situations in which developers would benefit from tools that could analyze partially-implemented systems: those for which some components are given only as high-level specifications while others are fully implemented in a programming language. In this paper, we propose a method for analyzing such partially-implemented real-time systems. We consider real-time concurrent systems for which some components are implemented in Ada and some are partially specified using regular expressions and graphical interval logic (GIL), a real-time temporal logic. We show how to construct models of the partially-implemented systems that account for such properties as run-time overhead and scheduling of processes, yet support tractable analysis of nontrivial programs. The approach can be fully automated, and we illustrate it by analyzing a small example.

On the use of a formal requirements engineering language: The Generalized Railroad Crossing Problem

In this paper, we report on the use of theAlbert II requirements specification language through the handling of the Generalized Railroad Crossing case study. This formal language is based on an ontology of concepts used for capturing requirements inherent in real-time, distributed systems. Because of itsnaturalness, the language supports a direct mapping of customers' informal needs onto formal statements, without having to introduce artificial elements. The language is founded on a formal framework (real-time temporal logic) which supports the reasoning process of the analyst during the elaboration of the specification. Such support for the reasoning is illustrated in the context of a goal-oriented approach adopted for the elaboration of the case study.

A specification architecture for multimedia systems in Open Distributed Processing

The field of distributed systems is now entering a stage of maturity with work focusing on standards for Open Distributed Processing (ODP). However, it is still important that standardisation remains responsive to new technological demands such as the emergence of distributed multimedia computing. This paper focuses on the likely impact of multimedia computing on formal description within ODP. In particular, a specification architecture is proposed for the formal specification and verification of quality of service and more general real-time concerns in distributed multimedia systems. This specification architecture exhibits a separation of concerns between the specification of behaviour and requirements and also between the specification of abstract behaviour and real-time concerns. The architecture also supports refinement to the computational language defined by the ODP standard. It is important to stress that the architecture does not prescribe the use of specific formal notations or languages; particular specification disciplines can however be developed by populating the architecture with appropriate languages. The usefulness of this architecture is demonstrated by the development of such an approach based on LOTOS together with a real-time temporal logic, QTL. This is applied to a simple multimedia example.

Formal refinement patterns for goal-driven requirements elaboration

Requirements engineering is concerned with the identification of high-level goals to be achieved by the system envisioned, the refinement of such goals, the operationalization of goals into services and constraints, and the assignment of responsibilities for the resulting requirements to agents such as humans, devices and programs. Goal refinement and operationalization is a complex process which is not well supported by current requirements engineering technology. Ideally some form of formal support should be provided, but formal methods are difficult and costly to apply at this stage.This paper presents an approach to goal refinement and operationalization which is aimed at providing constructive formal support while hiding the underlying mathematics. The principle is to reuse generic refinement patterns from a library structured according to strengthening/weakening relationships among patterns. The patterns are once for all proved correct and complete. They can be used for guiding the refinement process or for pointing out missing elements in a refinement. The cost inherent to the use of a formal method is thus reduced significantly. Tactics are proposed to the requirements engineer for grounding pattern selection on semantic criteria.The approach is discussed in the context of the multi-paradigm language used in the KAOS method; this language has an external semantic net layer for capturing goals, constraints, agents, objects and actions together with their links, and an inner formal assertion layer that includes a real-time temporal logic for the specification of goals and constraints. Some frequent refinement patterns are high-lighted and illustrated through a variety of examples.The general principle is somewhat similar in spirit to the increasingly popular idea of design patterns, although it is grounded on a formal framework here.

Formal specification and verification of multimedia systems in open distributed processing

The field of distributed systems is now entering a stage of maturity with work focusing on standards for Open Distributed Processing (ODP). However, it is still important that standardization remains responsive to new technological demands such as the emergence of distributed multimedia computing. This paper focuses on the likely impact of multimedia computing on formal description within ODP. In particular, a framework is proposed for the formal specification and verification of quality of service and more general real-time concerns in distributed multimedia systems. This framework exhibits a separation of concerns between the specification of behaviour and requirements and also between the specification of abstract behaviour and real-time concerns. The usefulness of this framework is demonstrated by the development of an approach based on LOTOS together with a real-time temporal logic, QTL.

Using a Real-Time Framework to Verify the Properties of Grafcet

Grafcet is one of the most widely used models for the specification and the implementation of control in manufacturing systems. Nevertheless, Grafcet is not well adapted to the analysis and the verification of safety and liveness properties because it is not based on a mathematical formalism. This article proposes an approach based on the use of the “Timed Transition Model (TTM)/Real-Time Temporal Logic (RTTL)” formal framework as a support to the analysis and verification of properties of Grafcet controlled manufacturing systems.

An object-oriented concept for real-time control of an FMS

The concept of an object-oriented database and a knowledge system represented by production rules is described. The design of the database is problem oriented to FMS and contains the predefined objects' classes. The production rules are divided into three groups: process knowledge rules (which create a dynamic state model of the resources), production plan rules (which define precondition of the operations), and expert knowledge rules (which create a reasoning model for solving a faulty situation). The real-time temporal logic as an assertion language for the specification of the behaviour of the manufacturing processes is described, and the verification of this behaviour in the stage of simulation is described.

Real-Time Logics: Complexity and Expressiveness

The theory of the natural numbers with linear order and monadic predicates underlies propositional linear temporal logic. To study temporal logics that are suitable for reasoning about real-time systems, we combine this classical theory of infinite state sequences with a theory of discrete time, via a monotonic function that maps every state to its time. The resulting theory of timed state sequences is shown to be decidable, albeit nonelementary, and its expressive power is characterized by ω-regular sets. Several more expressive variants are proved to be highly undecidable. This framework allows us to classify a wide variety of real-time logics according to their complexity and expressiveness. Indeed, it follows that most formalisms proposed in the literature cannot be decided. We are, however, able to identify two elementary real-time temporal logics as expressively complete fragments of the theory of timed state sequences, and we present tableau-based decision procedures for checking validity. Consequently, these two formalisms are well-suited for the specification and verification of real-time systems.

TYPED TIMED INPUT/OUTPUT AUTOMATA IN REAL-TIME, CYBERNETIC EXPLANATION

This paper presents a basis for real-time, cybernetic explanation in terms of typed timed input/output automata (tTAi/o). These are a form of Müller automata with typed states, input, and output. The typing of a tTAi/o is carried out intuitionistically in the tradition begun by Martin-Löf. The explanation of choice in the behavior specified by a tTAi/os is given in terms of the choice operators from Girard's linear logic. The meaning of a timed behavior specified by a tTAi/os is explained with real-time temporal logic. As a result of this approach to cybernetic explanation, a framework for reasoning about time for a specified behavior is given.

An Object-Oriented Conception of a Real-Time Control of FMS

The conception of the object-oriented database and the knowledge system represented by production rules is described. The design of the database is problem oiented to FMS and contains the predefined objects' classes. The production rules are dIVIded Into three groups: process knowledge rules (they create a dynamic state model of the resources), production plan rules (they define precondition of the operations) and expert knqwledge rules (they create a reasoning model for solving a faulty situation). the real-time temporal logic as an assertion language for the specification of the behaviour of the manufacturing processes is described, and the verification of these behaviour in the stage of simulation is described.

A verifier for real-time properties

The purpose of this paper is (a) to present a prototype verifier for real-time temporal logic properties, and (b) to improve the average efficiency of the verification procedures over past results where possible. A process control example is used to illustrate the use of the verifier. The verifier is applicable to real-time systems with finite state spaces.

A temporal logic-based model of event-driven nets

In this paper, a formal model of Event-Driven Nets (EDNs) is presented. Real-time temporal logic is used for representing both the behavior and structure of a modelled net. The structure of the net is defined using a set of executable predicates formed over state and pulse temporal variables. Considering this formal model, we outline an implementation of an interpretation technique for the EDN structural description. Finally, the modelling power of EDNs is demonstrated by the behavioral and performance simulation of a simple distributed computer system.

MODELING TIMED BEHAVIOR IN REAL-TIME SYSTEMS WITH TEMPORAL LOGIC

This article presents graphic as well as assertional representations of the timed behavior of a real-time system. It introduces finite, directed, labeled graphs called temporal I/O automata (TAi/o) to provide a visual means of modeling system behavior. A real-time system is modeled as a collection of communicating TAi/os. A TAi/o is associated with an external clock, which makes it possible to formulate hard, real-time constraints on actions performed by a system. Timing constraints provide control engineers with a means of measuring the responsive ness of a system to its environment. This article suggests how real-time temporal logic can be used to describe system behavior concisely. Temporal specifications provide (1) a means of verifying the; correctness of a system design, and (2) a basis for constructing implementations of system designs. The behavior of control systems for autonomous vehicles guided by visual feedback are described graphically with TAi/oS and textually with temporal logic formulas. Suggestions on how such control systems can be implemented in distributed Ada are also presented.

A framework for real-time discrete event control

The TTM/RTTL (timed transition model with real-time temporal logic) framework is presented for modeling, specifying, and analyzing real-time discrete-event systems. TTMs are used to represent the process of the plant and its controller. RTTL is the assertion language for specifying plant behavior and verifying that a controller satisfies the specification. The framework adapts features from the program verification literature which are useful for posing problems of interest to the control engineer, such as modular synthesis and design. Examples are used to illustrate the ideas presented. The authors' published analytical results are summarized and referenced. >

Deciding properties of timed transition models

Real-time distributed systems are modeled by a times transition model (TTM). For any finite-state TTM, decision procedures are provided for checking a small but important class of properties (specified in real-time temporal logic). The procedures are linear in the size of the system reachability graph. The class of properties includes invariance, precedence, eventuality and real-time response specifications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modularity in the ESM/RTL Framework for Real-Time Systems

The ESM/RTL framework uses extended state machines (ESMs) for representing real-time discrete event processes in both the object to be controlled (the plant) and the controlling software (the controller). Real-time temporal logic (RTL) is used as the assertion language for specifying required plant behaviour and verifying that the controller satisfies this specification.In this paper, a first step towards modularizing the ESM/RTL framework is taken by developing a method to construct higher level ESMs from basic ESMs. ESMs are interpreted as generators of trajectories, and this interpretation can be used to provide an operational semantics for an ESM at any level. The paper concludes with a brief discussion of how the framework supports modular reasoning in RTL.