Properties Of Real-time Systems Research Articles

System Auditing for Real-Time Systems

System auditing is an essential tool for detecting malicious events and conducting forensic analysis. Although used extensively on general-purpose systems, auditing frameworks have not been designed with consideration for the unique constraints and properties of Real-Time Systems (RTS). System auditing could provide tremendous benefits for security-critical RTS. However, a naive deployment of auditing on RTS could violate the temporal requirements of the system while also rendering auditing incomplete and ineffectual. To ensure effective auditing that meets the computational needs of recording complete audit information while adhering to the temporal requirements of the RTS, it is essential to carefully integrate auditing into the real-time (RT) schedule. This work adapts the Linux Audit framework for use in RT Linux by leveraging the common properties of such systems, such as special purpose and predictability. Ellipsis , an efficient system for auditing RTS, is devised that learns the expected benign behaviors of the system and generates succinct descriptions of the expected activity. Evaluations using varied RT applications show that Ellipsis reduces the volume of audit records generated during benign activity by up to 97.55% while recording detailed logs for suspicious activities. Empirical analyses establish that the auditing infrastructure adheres to the properties of predictability and isolation that are important to RTS. Furthermore, the schedulability of RT tasksets under audit is comprehensively analyzed to enable the safe integration of auditing in RT task schedules.

Alvis Approach to Modeling and Verification of Real-Time Systems Running on Single-Processor Environment

Alvis is a formal modelling language developed primarily for modelling concurrent systems including real-time systems. The prepared model is compiled and the resulting runnable model allows, e.g., to generate the state space and to verify the model using model checking techniques. The default version assumes that each system component (agent) executes its computations in parallel and that the hardware platform is not a shared resource. This paper describes an alternative approach in which agents remain concurrent, but compete for access to a single shared processor. This situation significantly affects the correctness of the system, in particular from the perspective of the timing properties of real-time systems. The key element of the presented solution is the fact that changing the runtime environment comes down to changing compiler options and does not require changes to the original model. This paper presents a method of designing Alvis language models for a single-processor hardware platform. The presented concepts are illustrated with examples.

An UML Based Performance Evaluation of Real-Time Systems Using Timed Petri Net

Performance is a critical non-functional parameter for real-time systems and performance analysis is an important task making it more challenging for complex real-time systems. Mostly performance analysis is performed after the system development but an early stage analysis and validation of performance using system models can improve the system quality. In this paper, we present an early stage automated performance evaluation methodology to analyse system performance using the UML sequence diagram model annotated with modeling and analysis of real-time and embedded systems (MARTE) profile. MARTE offers a performance domain sub-profile that is used for representing real-time system properties essential for performance evaluation. In this paper, a transformation technique and transformation rules are proposed to map the UML sequence diagram model into a Generalized Stochastic Timed Petri net model. All the transformation rules are implemented using a metamodel based approach and Atlas Transformation Language (ATL). A case study from the manufacturing domain a Kanban system is used for validating the proposed technique.

Modeling and realization of real time electronic countermeasure simulation system based on SystemVue

In this paper, we proposed a new design scheme of real time electronic countermeasure simulation system. This paper mainly expounds the modeling and realization methods of each part of the whole simulation system, and the real-time property of system has been lucubrated. Electronic countermeasure simulation system is the key part of military training of individuals; it can also allow the realistic evaluation of the performance of modern equipments and techniques. As a proof, we have drawn up a series of simulation scenarios, such as radar electronic reconnaissance simulation scenario, to explain the feasibility and the superiority of our modeling scheme in this paper.

Multi-Resource Modeling of Real-Time Software Based on Resource Timed Process Algebra

With the process of non-functional properties research on real-time systems, multi-resource estimation and analysis of real-time systems become a hotspot. Process algebra is a formal method that is fit for analyzing the functional properties of real-time systems, but it cannot analyze the multi-resource properties. Resource timed process algebra (RTPA) proposed in this paper can handle it efficiently by extending multi-resource semantics on timed communicating sequential process (TCSP). The multi-resource consumption of real-time instruction is mapped into the resource vector of RTPA, and then the multi-resource consumption of real-time systems can be modeled and optimized by using RTPA; the resource optimal checking algorithms are proposed to check the multi-resource satisfiability of instructions and calculate the minimum resource and accumulated resource of real-time systems. This formal method improves the accuracy and efficiency of multi-resource calculation, and the calculation results can be further used to quantitatively analyze and optimize the multi-resource consumption of real-time systems.

A Process Algebraic Approach to Resource-Parameterized Timing Analysis of Automotive Software Architectures

Modern automotive software components are often first developed by different suppliers and then integrated under limited resources by a manufacturer. The integration of software components under various resource configurations is prone to timing errors because the components are resources independently designed by the supplier and viewed by the manufacturer as black boxes during the integration stage, so that imposing resource constraints/requirements on their behavior is a challenge. This paper introduces an engineering awareness environment for the analysis of automotive systems with respect to two perspectives: 1) time-aware design models that correspond to the supplier perspective; and 2) resource-aware design models imposed by the manufacturer during integration. To this end, first we propose two timed behavioral models, a time-constrained model ( $\mathsf{TcM}$ ) and a resource-constrained model ( $\mathsf{RcM}$ ) that are extended from a functional model ( $\mathsf{FM}$ ). A timing analysis of applications can hence be conducted incrementally by adopting the separation of concerns principle coming from the model-driven architectures (MDAs). Second, given a basic application component description of AUTomotive Open System Architecture with timing properties, we specify how to define the behavior of the basic components as process terms using a process algebra, algebra of communicating shared resources with value passing (ACSR-VP), in order to exploit the description capability of the language for both timing aspects and resource-constrained aspects of a system. As a result, a timed behavioral model of a system can be seamlessly refined by various resource configurations, and both platform-independent and platform-dependent timing properties of real-time systems can be analyzed in a consistent and efficient manner.

Specifying safety-critical systems with a decidable duration logic

Punctual timing constraints are important in formal modelling of safety-critical real-time systems. But they are very expensive to express in dense time. In most cases, punctuality and dense-time lead to undecidability. Efforts have been successful to obtain decidability; but the results are either non-primitive recursive or nonelementary. In this paper we propose a duration logic which can express quantitative temporal constraints and punctuality timing constraints over continuous intervals and has a reasonable complexity. Our logic allows most specifications that are interesting in practice, and retains punctuality. It can capture the semantics of both events and states, and incorporates the notions duration and accumulation. We call this logic ESDL (the acronym stands for Event- and State-based Duration Logic). We show that the satisfiability problem is decidable, and the complexity of the satisfiability problem is NEXPTIME. ESDL is one of a few decidable interval temporal logics with metric operators. Through some case studies, we also show that ESDL can specify many safety-critical real-time system properties which were previously specified by undecidable interval logics or their decidable reductions based on some abstractions.

Modeling and Analysis of Real-Time Software Based on Resource Timed Communicating Sequential Process

With the progress of low-power research on real-time systems, the estimation and analysis of energy consumption of real-time systems becomes a hot topic. Process Algebra is a formal method fit for analyzing the functional properties of real-time systems, but it can not analyze the energy consumption properties. This paper proposes a formal method support for modeling and analyzing energy consumption of real-time software. Resource Timed Communicating Sequential Process (RTCSP) is proposed in this paper can handle it efficiently by extending resource information on Timed Communicating Sequential Process (TCSP). In this paper, the power consumption of instructions in real-time systems is mapped into the resource of RTCSP, the energy consumption of real-time software can be modeled and optimized by using RTCSP, the optimal path algorithm is proposed to calculate the minimum energy consumption reachability path of real-time systems. This formal method improves the accuracy and efficiency of energy calculation, the calculation results can be used to quantitatively analyze and optimize the energy consumption of real-time systems.

On Verification of Linear Occurrence Properties of Real-Time Systems

Duration Calculus of Weakly Monotonic Time (WDC) is an extension of DC to allow description of discrete processes where several steps of computation can occur at the same time point. In this paper, we introduce Linear Occurrence Invariants (LOI) using WDC and give an algorithm to check real-time automata for LOI by solving integer programming problems. LOI can be used effectively to specify system requirements in some cases including when the system is considered under the true synchrony assumption. We also extend WDC probabilistically to express dependability requirements of real-time systems and develop a technique to check deterministic probabilistic real-time automata for a class of probabilistic WDC formulas.

SAT-based Abstraction Refinement for Real-time Systems

In this paper, we present an abstraction refinement approach for model checking safety properties of real-time systems using SAT-solving. We present a faithful embedding of bounded model checking for systems of timed automata into propositional logic with linear arithmetic and prove correctness. With this logical representation, we achieve a linear-size representation of parallel composition and introduce a quick abstraction technique that works uniformly for clocks, events, and states. When necessary, abstractions are refined by analysing spurious counterexamples using a promising extension of counterexample-guided abstraction refinement with syntactic information about Craig interpolants. To support generalisations, our overall approach identifies the algebraic and logical principles required for logic-based abstraction refinement.

Model and algorithm for efficient verification of high-assurance properties of real-time systems

In this paper, we present a new compositional verification methodology for efficiently verifying high-assurance properties such as reachability and deadlock freedom of real-time systems. In this methodology, each component of real-time systems is initially specified as a timed automaton and it communicates with other components via synchronous and/or asynchronous communication channels. Then, each component is analyzed by a generation of its state-space graph which is formalized as a new state-space representation model called Multiset Labeled Transition Systems (MLTSs). Afterward, the state spaces of the components are hierarchically composed and simplified through a composition algorithm and a set of condensation rules, respectively, to get a condensed state space of the system. The simplified state spaces preserve equivalence with respect to deadlock and reachable states. Such equivalence is assured by our reduction theories called IOT-failure equivalence and IOT-state equivalence. To show the performance of our methodology, we developed a verification tool RT-IOTA and carried out experiments on some benchmarks such as CSMA/CD protocol, a rail-road crossing, an alternating bit-protocol, etc. Specifically, we look at the time taken to generate the statespace, the size of the state space, and the amount of reduction achieved by our condensation rules. The results demonstrate the strength of our new technique in dealing with the state-explosion problem.

SIMULATION OF STEVEDORING WORK IN THE KLAIPEDA OIL TERMINAL

The paper presents the approach of developing simulation models of stevedoring work in oil terminal using aggregate approach and simulation system ARENA. Aggregate approach permits to develop formal specification of simulated systems. Aggregate specification of the system is presented as a set of interacting piece-linear aggregates. Controlling sequences are used for formal description of each piece-linear aggregate. Transformation of aggregate formal specification to ARENA system operators permits to develop a simulation model. The developed model permits to evaluate characteristics of the Klaipeda oil terminal which are used both in queuing theory and analysing timing properties of real-time systems.

An integrated framework for information-centred human-machine systems analysis

In emergency management, operators and commanders must rely on dynamic, distributed systems and organisations for safe and effective mission accomplishment. Commanders and operators often experience extreme risk exposure, and coping with environmental hazards, fear, exhaustion and compulsion is part of their profession. They routinely handle highly ambiguous decision situations, where critical demands are inflicted upon their cognitive abilities and response times. In the future, they will make decisions in situations where operational and system characteristics are highly dynamic and non-linear, i.e. small actions or decisions may have serious and irreversible consequences for the entire mission. Commanders and operators are required to manage true real-time system properties at all levels, individual operators, stand-alone technical systems, higher-order integrated socio-technical systems and joint operations forces alike. Coping with these conditions in performance assessment, system development and operational testing is a challenge for practitioners, instructors and researchers. Using a monotheory approach, such as classic decision theory and multi-attribute utility theory, is nearly impossible. New results, new measurement techniques and new methodological breakthroughs facilitate a more accurate and deeper understanding, generating new and updated models and paradigms. This in turn generates theoretical advances. Some good examples of successful polytheory approaches are found in the research areas of cognitive systems engineering, systems theory, and psychophysiology, and in the fields of dynamic, distributed decision making and naturalistic decision-making. A successful attempt to integrate these areas into a coherent framework, Action Control Theory (ACT), is described.

Extending the SCR Method for Real-Time Systems

We propose timed SCR specifications, which are a generalization of SCR specifications, intended to specify quantitative timing properties of real-time systems. We extend the tabular notation of the...

Deductive verification of real-time systems using STeP

We present a modular framework for proving temporal properties of real-time systems, based on clocked transition systems and linear-time temporal logic. We show how deductive verification rules, verification diagrams, and automatic invariant generation can be used to establish properties of real-time systems in this framework. We also discuss global and modular proofs of the branching-time property of non-Zenoness. As an example, we present the mechanical verification of the generalized railroad crossing case study using the Stanford Temporal Prover, STeP.

Verification of clocked and hybrid systems

This paper presents a new computational model for real-time systems, called the clocked transition system (CTS) model. The CTS model is a development of our previous timed transition model, where some of the changes are inspired by the model of timed automata. The new model leads to a simpler style of temporal specification and verification, requiring no extension of the temporal language. We present verification rules for proving safety a nd liveness properties of clocked transition systems. All rules are associated with verification diagrams. The verification of response properties requires adjustments of the proof rules developed for untimed systems, reflecting the fact that progress in the real time systems is ensured by the progress of time and not by fairness. The style of the verification rules is very close to the verification style of untimed systems which allows the (re)use of verification methods and tools, developed for u ntimed reactive systems, for proving all interesting properties of real-time systems. We conclude with the presentation of a branching-time based approach for verifying that an arbitrary given CTS isnon-zeno. Finally, we present an extension of the model and the invariance proof rule for hybrid systems.

Specification of Real-Time Systems in UML

We introduce time semantics into UML class and statechart diagrams. This extends the expressiveness of UML for specification of real-time systems and allows to specify verification properties of real-time systems by means of Timed Computation Tree Logic. We furthermore propose a way to collect stereotypes for specification of real-time systems. The approach is illustrated by a case study.

Generating Real-Time Software Test Cases by Time Petri Nets

Although real-time software must satisfy not only functional correctness requirements but also timeliness requirements, much recent real-time research has focused on analysis rather than testing. During the execution of real-time software, a sequence of events due to time take place between the concurrent processes. Because concurrent processes are unpredictable, multiple executions of a given real-time software with the same test cases may produce different results. This nondeterministic execution behaviour always creates problems in real-time software testing. This paper explores real-time software testing, combining decomposition of Petri nets model with expansion of its time criterion. It provides guidelines for handling the nondeterministic properties of real-time systems using time Petri nets model, rules for decomposing the Petri nets model into independent segment groups, and a description of the way test cases are generated using independent segment group and time variation method.

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.

Model Checking via Reachability Testing for Timed Automata

In this paper we develop an approach to model-checking for timed automata via reachability testing. As our specification formalism, we consider a dense-time logic with clocks. This logic may be used to express safety and bounded liveness properties of real-time systems. We show how to automatically synthesize, for every logical formula phi, a so-called test automaton T_phi in such a way that checking whether a system S satisfies the property phi can be reduced to a reachability question over the system obtained by making T_phi interact with S. <br />The testable logic we consider is both of practical and theoretical interest. On the practical side, we have used the logic, and the associated approach to model-checking via reachability testing it supports, in the specification and verification in Uppaal of a collision avoidance protocol. On the theoretical side, we show that the logic is powerful enough to permit the definition of characteristic properties, with respect to a timed version of<br />the ready simulation preorder, for nodes of deterministic, tau-free timed automata. This allows one to compute behavioural relations via our model-checking technique, therefore effectively reducing the problem of checking the existence of a behavioural relation among states of a timed automaton to a reachability problem.