Real-time Specification Language Research Articles

A formal framework for modeling and validating Simulink diagrams

Abstract Simulink has been widely used in industry to model and simulate embedded systems. With the increasing usage of embedded systems in real-time safety-critical situations, Simulink becomes deficient to analyze (timing) requirements with high-level assurance. In this article, we apply Timed Interval Calculus (TIC), a real-time specification language, to complement Simulink with TIC formal verification capability. We elaborately construct TIC library functions to model Simulink library blocks which are used to compose Simulink diagrams. Next, Simulink diagrams are automatically transformed into TIC models which preserve functional and timing aspects. Important requirements such as timing bounded liveness can be precisely specified in TIC for whole diagrams or some components. Lastly, validation of TIC models can be rigorously conducted with a high degree of automation using a generic theorem prover. Our framework can enlarge the design space by representing environment properties to open systems, and handle complex diagrams as the analysis of continuous and discrete behavior is supported.

Periodic Linear Programming with applications to real-time scheduling

In this paper we introduce a new mathematical modelling technique called Periodic Linear Programming; the periodic properties of Periodic Linear Programs (PLPs) permit the specification of inter-period constraints in embedded systems, in a straightforward and natural manner. We analyse PLPs in which the relationship between program variables is restricted to the class of difference constraints. Our analysis establishes that such PLPs can be reduced to simple linear programs, and hence decided in polynomial time. The class of difference constraints is extremely important from the perspective of embedded systems design, in that it permits the specification of complex timing constraints in real-time specification languages. A PLP can be thought of as a finite-description tool that represents infinite-state systems; although we use this tool purely for the purpose of modelling real-time scheduling problems, PLPs also find applications in other areas, such as concurrency design. In studying this programming paradigm, we develop novel techniques that, to the best of our knowledge, are not part of the literature. We build on the PLP structure to introduce a generalisation called Periodic Quantified Linear Programming; this programming paradigm permits the specification and analysis of uncertainty in the parameters of a PLP. Consequently, a Periodic Quantified Linear Program (PQLP) is the natural modelling tool to capture the requirements of periodic, embedded systems that are characterised by uncertainty in the execution times of processes, periodicity and relative timing constraints. In this paper, we use the PQLP structure to model and solve the periodic version of the zero-clairvoyant scheduling problem. Modelling uncertainty in the problem description is a typical technique used to incorporate a measure of fault-tolerance in the specification.

Proof assistance for real-time systems using an interactive theorem prover

This paper discusses the adaptation of the PVS theorem prover for performing analysis of real-time systems written in the ASTRAL formal specification language. Several issues arose during the encoding of ASTRAL that are relevant to the encoding of many real-time specification languages such as encoding formulas as types, handling partial functions, dealing with noninterleaved concurrency, and defining irregular operators. These issues and possible solutions are presented as well as how they were handled in the ASTRAL encoding. A translator was written that translates any ASTRAL specification into its corresponding PVS encoding. After performing the proofs of several systems using their translations, PVS strategies were developed to automate the proofs of certain types of properties. In particular, strategies are presented for fully automating the proofs of certain classes of untimed properties. In addition, strategies were developed for partially automating the derivation of timed executions using transition steps. The encoding was used as the basis for a fully automated transition sequence generator tool, which has a wide variety of applications.

Model-Generation of a Fictitious Clock Real-Time Logic Using Sharing Trees

We present first the logic mtl, a real-time temporal logic that is at the heart of the real-time specification language Albert. Since this logic is undecidable, we approximate it (using the theory of Abstract Interpretation) by its fictitious clock counterpart, MTLfc.We then present a symbolic tableau-based model generation decision procedure in ECLFC, which is theoretically optimal. In practice however, we see that the introduction of integer-valued prophecy variables will make it more efficient. From these variables, we reconstruct by reverting the process a logic that we call ExpSpace, which can be decided in PSpace, and has the same expressivity as MTLfc. Theory thus shows that memory space is the critical factor. However, the classical compaction of memory space by BDDs is not ideal here, since our integer variables would need to be encoded by booleans. Therefore, we use Sharing Trees instead, a compact data structure that can accommodate arbitrary data types. Preliminary results on this implementation are reported.

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.

Integrating methods for the design of real-time systems

With the aim of designing complex real-time systems, we investigate the integration of conceptual modeling techniques, formal specification, and compositional verification. A constructive transformation is defined from a conceptual meta-model to a real-time specification language. Refinement steps can be verified formally by means of compositional proof rules. The approach is illustrated by the design of a mine pump control system.

Time-constrained buffer specifications in CSP + T and timed CSP

A finite buffer with time constraints on the rate of accepting inputs, producing outputs, and message latency is specified using both Timed CSP and a new real-time specification language, CSP + T, which adds expressive power to some of the sequential aspects of CSP and allows the description of complex event timings from within a single sequential process. On the other hand, Timed CSP encourages event-timing descriptions to be built up in a constraint-oriented manner with the parallel composition of several processes. Although these represent two complementary specification styles, both provide valuable insights into the specification of complex event timings.