Timed Process Algebra Research Articles

Abstracting IoT protocols using timed process algebra and SPIN model checker

Abstracting IoT protocols using timed process algebra and SPIN model checker

Axiomatizing Maximal Progress and Discrete Time

Milner's complete proof system for observational congruence is crucially based on the possibility to equate τ divergent expressions to non-divergent ones by means of the axiom recX.(τ.X + E) = recX.τ.E. In the presence of a notion of priority, where, e.g., actions of type δ have a lower than silent τ actions, this axiom is no longer sound. Such a form of is, however, common in timed process algebra, where, due to the interpretation of δ as a time delay, it naturally arises from the maximal progress assumption. We here present our solution, based on introducing an auxiliary operator pri(E) defining a priority scope, to the long time open problem of axiomatizing using standard observational congruence: we provide a complete axiomatization for a basic process algebra with and (unguarded) recursion. We also show that, when the setting is extended by considering static operators of a discrete time calculus, an axiomatization that is complete over (a characterization of) finite-state terms can be developed by re-using techniques devised in the context of a cooperation with Prof. Jos Baeten. Research partly supported by the H2020-MSCA-RISE project ID 778233 Behavioural Application Program Interfaces (BEHAPI).

Formal Models of the OSPF Routing Protocol

We present three formal models of the OSPF routing protocol. The first two are formalised in the timed process algebra T-AWN, which is not only tailored to routing protocols, but also specifies protocols in pseudo-code that is easily readable. The difference between the two models lies in the level of detail (level of abstraction). From the more abstract model we then generate the third model. It is based on networks of timed automata and can be executed in the model checker Uppaal.

Formalising the Optimised Link State Routing Protocol

Routing protocol specifications are traditionally written in plain English. Often this yields ambiguities, inaccuracies or even contradictions. Formal methods techniques, such as process algebras, avoid these problems, thus leading to more precise and verifiable descriptions of protocols. In this paper we use the timed process algebra T-AWN for modelling the Optimised Link State Routing protocol (OLSR) version 2.

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.

Formal performance evaluation of the Map/Reduce framework within cloud computing

The recent appearance, evolution and massive expansion of social media-based technologies, in conjunction with what currently is known as Internet of Things, results in a vertiginous data production. One of the main contributions to address this matter has been the Hadoop framework (which implements the Map/Reduce paradigm), especially when used in conjunction with Cloud computing environments. In this paper, a comprehensive and rigourous study of the Map/Reduce framework using formal methods is presented. Specifically, the Timed Process Algebra BTC is used, and the resulting formal model is evaluated with a real social media data Hadoop-based application. Moreover, the formal model is validated by carrying out several experiments on a real private Cloud environment. Finally, the formal model outcomes are harnessed to determine the best performance---cost agreement in a real scenario. Results show that the proposed model enables to determine in advance both the performance of a Hadoop-based application within Cloud environments and the best performance---cost agreement.

PADS: An approach to modeling resource demand and supply for the formal analysis of hierarchical scheduling

As real-time embedded systems become more complex, resource partitioning is increasingly used to guarantee real-time performance. Recently, several compositional frameworks of resource partitioning have been proposed using real-time scheduling theory with various notions of real-time tasks running under restricted resource supply environments. However, these real-time scheduling-based approaches are limited in their expressiveness in that, although capable of describing resource-demand tasks, they are unable to model resource supply. This paper describes a process algebraic framework PADSfor reasoning about resource demand and resource supply inspired by the timed process algebra ACSR. In ACSR, real-time tasks are specified by enunciating their consumption needs for resources. To also accommodate resource-supply processes in PADS, given a resource c p u , we write c p u ¯ to denote the availability of c p u for a requesting task process. Using PADS, we define a supply-demand relation where a pair ( T , S ) belongs to the relation if the demand process T can be scheduled under supply S . We develop a theory of compositional schedulability analysis as well as a technique for synthesizing an optimal supply process for a set of tasks. Furthermore, we define ordering relations between supplies which describe when a supply offers more resource capacity than another. With this notion it is possible to formally represent hierarchical scheduling approaches that assign more “generous” resource allocations to tasks in exchange for a simple representation. We illustrate our techniques via a number of examples.

Non-functional properties in the model-driven development of service-oriented systems

Systems based on the service-oriented architecture (SOA) principles have become an important cornerstone of the development of enterprise-scale software applications. They are characterized by separating functions into distinct software units, called services, which can be published, requested and dynamically combined in the production of business applications. Service-oriented systems (SOSs) promise high flexibility, improved maintainability, and simple re-use of functionality. Achieving these properties requires an understanding not only of the individual artifacts of the system but also their integration. In this context, non-functional aspects play an important role and should be analyzed and modeled as early as possible in the development cycle. In this paper, we discuss modeling of non-functional aspects of service-oriented systems, and the use of these models for analysis and deployment. Our contribution in this paper is threefold. First, we show how services and service compositions may be modeled in UML by using a profile for SOA (UML4SOA) and how non-functional properties of service-oriented systems can be represented using the non-functional extension of UML4SOA (UML4SOA-NFP) and the MARTE profile. This enables modeling of performance, security and reliable messaging. Second, we discuss formal analysis of models which respect this design, in particular we consider performance estimates and reliability analysis using the stochastically timed process algebra PEPA as the underlying analytical engine. Last but not least, our models are the source for the application of deployment mechanisms which comprise model-to-model and model-to-text transformations implemented in the framework VIATRA. All techniques presented in this work are illustrated by a running example from an eUniversity case study.

Liveness of a mutex algorithm in a fair process algebra

In earlier work, we have shown that two variants of weak fairness can be expressed comparatively easily in the timed process algebra PAFAS. To demonstrate the usefulness of these results, we complement work by Walker (Form Asp Comput 1:273–292, 1989) and study the liveness property of Dekker’s mutual exclusion algorithm within our process algebraic setting. We also present some results that allow to reduce the state space of the PAFAS process representing Dekker’s algorithm, and give some insight into the representation of fair behaviour in PAFAS.

Improving performance in flexible manufacturing systems

The need for flexible manufacturing systems (FMSs) has become of utmost importance over the last years due to the fierce competition present in the manufacturing industry as well as the ever decreasing product life spans and the markets attempts to respond to customers’ changing needs. These systems allow us to react quickly to changes, however this flexibility costs both time and money. Given this fact, it would be desirable to reduce costs by testing potential implementations before using them. We will use a timed process algebra called BTC (for bounded true concurrency) to face up to this challenge. We have developed this algebra by extending CSP in order to consider the duration of actions and the context (resources) in which processes are executed. This new algebra is able to take into account that the resources in a system must be shared by all the processes. So, we can find two kinds of delays in the execution of a process: delays related to the synchronization of processes, and delays related to the allocation of resources. Once FMSs are specified by means of BTC, we will focus our attention on the performance of the system which will be variable depending on the number of available resources. For this, we have developed a performance algorithm and a tool which implements it. Three examples are used to show how an FMS can be specified and how the algorithm and the tool work, allowing us to obtain the best performance with the lowest cost.

Real Time Process Algebra with Urgency Executing Policy

Real time systems have a natural executing policy of urgency. However, real time process algebras of nowadays cannot specify this basic executing policy which limits their expressiveness. There is only one default policy called “maximal progress” in process algebras which is not enough to specify the behaviors of real time systems. Based on this, we propose a real time process algebra with urgency executing policy which can specify the behaviors of real time systems.

Quantifying Security for Timed Process Algebras

A quantification of process's security by quantification of an amount of information flow is defined and studied in the framework of timed process algebras. The resulting quantified security is compared with other (qualitative) security notions. Unprecise and limited observations are defined and discussed.

Model Checking of Real-Time Properties of Resource-Bound Process Algebra

The algebra of communicating shared resources (ACSR) is a timed process algebra which extends classical process algebras with the notion of a resource. In analyzing ACSR models, the existing techniques such as bisimulation checking and Hennessy-Milner Logic (HML) model checking are very important in theory of ACSR, but they are difficult to use for large complex system models in practice. In this paper, we suggest a framework to verify ACSR models against their requirements described in an expressive timed temporal logic. We demonstrate the usefulness of our approach with a real world case study.

Testing Semantics for RTPA

The language RTPA, Real Time Process Algebra, has been created to enable rigorous treatment of knowledge representation and manipulation in terms of to be I to have / to do in a formal and coherent framework. This language has been designed to cope with the three dimensions involved in the problem of software specification: (i) mathematical operations, (ii) event/process timing, and (iii) memory manipulation. In this paper we focus on giving a testing semantics to the second dimension: Process timing dimension. First, we will provide a SOS like operational semantics for the process relations of RTPA. Next, we will define what a test is and we will introduce a relation based on which tests are passed by processes. Finally, we will obtain an operational characterization that can be used as a first step to define a denotational sematics sound and complete with respect the testing semantics.

Probabilistic Information Flow Security

A formal model for description of probabilistic timing attacks is presented and studied. It is based on a probabilistic timed process algebra, on observations (mappings which make visible only a part of system behavior) and on an information flow. The resulting security properties are studied and compared with other security concepts.

Formal modelling and discrete-time analysis of BPEL web services

Web services are increasingly used for building enterprise information systems according to the Service Oriented Architecture (SOA) paradigm. We propose in this paper a tool-equipped methodology allowing the formal modelling and analysis of web services described in the BPEL language. The discrete-time transition systems modelling the behaviour of BPEL descriptions are obtained by an exhaustive simulation based on a formalisation of BPEL semantics using the Algebra of Timed Processes (ATP). These models are then analysed by model checking value-based temporal logic properties using the CADP toolbox. The approach is illustrated with the design of a web service for GPS navigation.

Model-based system analysis using Chi and Uppaal: An industrial case study

New methods and techniques are needed to reduce the integration and test effort (lead time, costs, resources) in the development of high-tech multi-disciplinary systems. To facilitate this effort reduction, a method called model-based integration and testing is being developed. The method allows to integrate formal and executable models of system components that are not yet physically realized with available realizations of other components. The combination of models and realizations is then used for early analysis of the integrated system by means of validation, verification, and testing. The analysis enables early detection and prevention of problems that would otherwise occur during real integration, resulting in a significant reduction of effort invested in the real integration and testing phases. This paper illustrates the application of the method to a realistic industrial case study, focusing on verification of the models obtained. We show how a system model has been developed for model-based integration and testing in the timed process algebra χ (Chi), and how certain behavioral properties of this model have been verified by the Uppaal model checker.

Predictable real-time software synthesis

Formal theories for real-time systems (such as timed process algebra, timed automata and timed petri nets) have gained great success in the modeling of concurrent timing behavior and in the analysis of real-time properties. However, due to the ineliminable timing differences between a model and its realization, synthesizing a software realization from a model in a predictable way is still a challenging research topic. In this article, we tackle this problem by solving a set of sub-problems. The solution is based on the theoretical results for property prediction proposed in Huang et al. (2003, Real-time property preservation in approximations of timed systems. In: Proceedings of 1st ACM and IEEE international conference on formal methods and models for codesign. IEEE Computer Society, Los Alamitos, pp 163–171) and Huang (2005, Predictability in real-time system design. PhD thesis, Eindhoven University of Technology, The Netherlands), where quantitative property relations are established between two absolute/relative “close” real-time systems. This theory basically implies that if two systems are “close”, they enjoy “similar” properties. These results cannot be directly applied in practice though, because a model and its realization typically have infinitely large absolute and relative timing differences. We show that this infinite time gap can be bridged through a sequence of carefully constructed intermediate time domains. Then the property-prediction results can be applied to any pair of adjacent time domains in the sequence. Consequently, real-time properties of the implementation can be predicted from the model. We propose two parameterized hypotheses to characterize the timing differences in the sequence and to guide a correctness-preserving design process. It is shown that these hypotheses can be incorporated in a concrete tool set. We demonstrate the feasibility of the predictable synthesis approach through the design of a railroad crossing system.

Resources in process algebra

The Algebra of Communicating Shared Resources (ACSR) is a timed process algebra which extends classical process algebras with the notion of a resource. It takes the view that the timing behavior of a real-time system depends not only on delays due to process synchronization, but also on the availability of shared resources. Thus, ACSR employs resources as a basic primitive and it represents a real-time system as a collection of concurrent processes which may communicate with each other by means of instantaneous events and compete for the usage of shared resources. Resources are used to model physical devices such as processors, memory modules, communication links, or any other reusable resource of limited capacity. Additionally, they provide a convenient abstraction mechanism for capturing a variety of aspects of system behavior. In this paper we give an overview of ACSR and its probabilistic extension, PACSR, where resources can fail with associated failure probabilities. We present associated analysis techniques for performing qualitative analysis (such as schedulability analysis) and quantitative analysis (such as resource utilization analysis) of process-algebraic descriptions. We also discuss mappings between probabilistic and non-probabilistic models, which allow us to use analysis techniques from one algebra on models from the other.

A Family of Resource-Bound Real-Time Process Algebras

The Algebra of Communicating Shared Resources (ACSR) is a timed process algebra which extends classical process algebras with the notion of a resource. It takes the view that the timing behavior of a real-time system depends not only on delays due to process synchronization, but also on the availability of shared resources. Thus, ACSR employs resources as a basic primitive and it represents a real-time system as a collection of concurrent processes which may communicate with each other by means of instantaneous events and compete for the usage of shared resources. Resources are used to model physical devices such as processors, memory modules, communication links, or any other reusable resource of limited capacity. Additionally, they provide a convenient abstraction mechanism for capturing a variety of aspects of system behavior. The resulting framework combines the areas of process algebra and real-time scheduling, and can facilitate the reasoning about systems that are sensitive to deadlines, process interaction and resource availability.In this paper we give an overview of ACSR and three of its extensions PACSR, P2ACSR and MCSR, which take into account probabilistic failures, power consumption and multi-capacity resources.