QoS specification of ODP binding objects

We present a QoS oriented notation suitable for the ODP framework. In particular, we focus on a computational view of objects: we consider systems described as configurations of interacting objects and we deal with two types of communications: message passing and flows. In message passing, signals (from one object to another) are conveyed through the (implicit) underlying infrastructure. This form of interaction is suitable for client/server applications where no strong real time or ordering constraints are needed from the communication infrastructure. In contract, in a flow type of communication, signals are conveyed through third party (binding) objects that may be explicitly called for in order to ensure specific QoS requirements needed by specific applications. A building blocks approach for the formal specification of binding objects in the ODP computational model is presented. The formal notation that is used is based on LOTOS extended with two features - real time and gate passing. These features are among the extensions that are currently studied in the ISO standardisation Formal Description Techniques group. We apply our building blocks approach to the specification of a multicast, multimedia binding object

Architectural notes: a framework for distributed systems development

This thesis develops a framework of methods and techniques for distributed systems development. This framework consists of two related domains in which design concepts for distributed systems are defined: the entity domain and the behaviour domain. In the entity domain we consider structures of functional entities and their interconnection, while in the behaviour domain we consider behaviour definition and structuring. An interaction in which we abstract from the particular responsibilities of the participating functional entities is considered as an action. Behaviours consist of actions, interactions and their relationships. Relationships between actions and interactions are defined in terms of causality relations. In each causality relation the conditions and constraints for an action or interaction to occur are defined. Two important behaviour structuring techniques have been identified from the possible ways causality relations can be distributed: causality-oriented behaviour composition and constraint-oriented behaviour composition. Causality-oriented behaviour composition consists of placing some conditions of an action and the action itself in different sub-behaviours. Constraint-oriented behaviour composition consists of placing parts of the conditions and constraints of an action in different sub-behaviours, such that this action is shared by these sub-behaviours. This thesis identifies milestones in the design process of distributed systems, as well as the design steps to move from one milestone to another. These design steps are characterized using the concepts of the entity and the behaviour domain. We identified two crucial design operations of the behaviour domain that support these design steps: behaviour refinement and action refinement. Behaviour refinement consists of introducing (internal) structure in the causality relations of reference actions of an abstract behaviour, but preserving their causality and exclusion relationships and their attribute values. Action refinement consists of replacing abstract actions by activities, such that the completion of these activities correspond to the occurrence of the abstract actions. One important characteristic of action refinement is the possibility of distributing attribute values of the abstract actions over actions of the activities that replace them in the concrete behaviours. The area of research, scope and objectives of this thesis are discussed in Chapter 1. The concept of design culture and its elements is introduced in this chapter in order to provide an overview of the important aspects of the design process. Entity domain, behaviour domain, and design milestones are introduced and discussed in Chapter 2. This chapter also discusses the global objectives of design steps, and the abstraction obtained by considering interactions between cooperating functional entities as actions of the interaction system between these entities. Action, action attributes, causality and exclusion are discussed in Chapter 3. This chapter shows how a behaviour can be defined in terms of the causality relations of its actions in a monolithic form. Causality-oriented behaviour composition is discussed in Chapter 4. Entries and exits of a behaviour are the mechanisms that make it possible to assign parts of a condition of an action and the action itself to different sub-behaviours. Constraint-oriented behaviour composition is discussed in Chapter 5. Decomposition possibilities of monolithic behaviours are systematically studied in this chapter. Behaviour refinement is discussed in Chapter 6. This chapter defines a method to obtain an abstraction of a concrete behaviour. This method can be used to check whether the concrete behaviour corresponds to a certain abstract behaviour. Action refinement is discussed in Chapter 7. This chapter identifies some activity forms, and define the rules for considering these activities as implementations of an abstract action. These rules are used in a method to derive an abstraction of a concrete behaviour in which the abstract actions are implemented as activities. This method can be used to check whether the concrete behaviour corresponds to a certain abstract behaviour. Chapter 8 discusses a design example that is meant to illustrate the use of our design concepts. The example is an interaction server, which is a component that supports the interaction between multiple functional entities. Chapter 9 draws some conclusions and revisits the design milestones of Chapter 2, showing alternatives for the design trajectory which have been created with the use of actions and interactions in a single framework

Distributed systems : architecture-driven specification using extended LOTOS

The thesis uses the LOTOS language (ISO International Standard ISO 8807) as a basis for the formal specification of distributed systems. Contributions are made to two key research areas: architecture-driven specification and LOTOS language extensions. The notion of architecture-driven specification is to guide the specification process by providing a reference-base of pre-defined domain-specific components. The thesis builds an infra-structure of architectural elements, and provides Extended LOTOS (XL) definitions of these elements. The thesis develops Extended LOTOS (XI.) for the specification of distributed systems. XL- is LOTOS enhanced with features for the formal specification of quantitative timing. probabilistic and priority requirements. For distributed systems, the specification of these ‘performance’ requirements, ran be as important as the specification of the associated functional requirements. To support quantitative timing features, the XL semantics define a global, discrete clock which can be used both to force events to occur at specific times, and to measure Intervals between event occurrences. XL introduces time policy operators ASAP (as soon as possible’ corresponding to “maximal progress semantics") and ALAP (late as possible'). Special internal transitions are introduced in XL semantics for the specification of probability, Conformance relations based on a notion of probabilization, together with a testing framework, are defined to support reasoning about probabilistic XL specifications. Priority within the XL semantics ensures that permitted events with the highest priority weighting of their class are allowed first. Both functional and performance specification play important roles in CIM (Computer Integrated Manufacturing) systems. The thesis uses a CIM system known as the CIM- OSA lntegrating Infrastructure as a case study of architecture-driven specification using XL. The thesis thus constitutes a step in the evolution of distributed system specification methods that have both an architectural basis and a formal basis

A hemimetric extension of simulation for semi-markov decision processes

Semi-Markov decision processes (SMDPs) are continuous-time Markov decision processes where the residence-time on states is governed by generic distributions on the positive real line. In this paper we consider the problem of comparing two SMDPs with respect to their time-dependent behaviour. We propose a hemimetric between processes, which we call simulation distance, measuring the least acceleration factor by which a process needs to speed up its actions in order to behave at least as fast as another process. We show that this distance can be computed in time O(n2(f(l)+k)+mn7), where n is the number of states, m the number of actions, k the number of atomic propositions, and f(l) the complexity of comparing the residence-time between states. The theoretical relevance and applicability of this distance is further argued by showing that (i) it is suitable for compositional reasoning with respect to CSP-like parallel composition and (ii) has a logical characterisation in terms of a simple Markovian logic

Hybrid process algebra

IV+276hlm.;24c

Sémantique compositionnelle et raffinement de systèmes temporisés : application aux automates temporisés d'UPPAAL et au langage FIACRE

Les systèmes temps-réel sont massivement impliqués dans de nombreuses applications, dont notre vie dépend comme les logiciels embarqués dans les voitures et les avions. Pour ces systèmes des erreurs inattendues ne sont pas acceptables. De ce fait, assurer la correction de ces systèmes est une tâche primordiale. Les systèmes temps-réel représentent un large spectre de systèmes automatisés dont la correction dépend de la ponctualité des événements (timeliness) et pas seulement de leurs propriétés fonctionnelles. Chaque événement doit être produit selon la date indiquée par la spécification du système. Les systèmes temps-réel sont concurrents et embarqués, et conçus comme un assemblage de composants en interaction. Malgré les progrès réalisés dans les techniques de model checking, la vérification et l'analyse des systèmes temps-réel représentent toujours un défi autant pour les chercheurs que les praticiens. Pour étudier le comportement des systèmes temps-réel, différents formalismes ont été considérés comme les automates temporisés, les réseaux de Petri temporisés et les algèbres de processus. Cela donne lieu à plusieurs points délicats concernant le raffinement, la composition et la vérification. Ces points représentent un champ de recherche intensif. Ma thèse présente une étude des systèmes temps-réel focalisée sur les notions de sémantique, de composition et de raffinement. Elle décrit nos efforts pour explorer et étendre les formalismes temps-réel. Nous avons abordé les concepts de base de la modélisation des systèmes temps réel tels que les variables partagées, la communication, les priorités, la dynamicité, etc. La contribution de cette thèse porte sur la définition d’un cadre formel pour raisonner sur la sémantique, la composition et le raffinement des systèmes temporisés. Nous avons instancié ce cadre pour le formalisme des automates temporisés et le langage Fiacre.Nowadays, real-time systems are intensively involved in many applications on which our life is dependent, like embedded software in cars and planes. For these systems unexpected errors are not acceptable. Real-time systems represent a large spectrum of automated systems of which correctness depends on the timing of events (timeliness) and not only on their functional properties. Each event must be produced on time. Realtime systems can be concurrent and embedded where different interactive modules and components are assembled together. Despite advances in model checking techniques, the verification and analysis of real-time systems still represent a strong challenge for researchers and practitioners. To study the behavior of real-time systems, different formalisms have been considered like timed automata, time Petri nets and timed algebra, and several challenges concerning refinement, composition and verification have emerged. These points represent an intensive field of research. This thesis describes our effort to explore and extend real-time formalisms. We have revisited real-time language semantics, focusing on composition and refinement. We have addressed high level concepts like shared variables, communication, priorities, dynamicity, etc. The main contribution consists of a theoretical study of timed systems where we establish a framework for reasoning on composition, refinement and semantics. We instantiate this framework for timed automata and the Fiacre language