Rolv Bræk

Service discovery and component reuse with semantic interfaces

Current trends in distributed computing and e-business processing suggest that many applications are evolving towards Service Oriented Computing (SOC) with technologies such as Web services. Services are autonomous platform-independent computational elements, and we observe an increasing need for core SOC technologies for dynamic discovery, selection, and composition of services. However, such technologies are often based on syntactic descriptions of the services and of their interfaces, which are insufficient to ensure that desired liveness properties are satisfied. In this paper, we propose an approach for the description, discovery, and selection of services based on role modeling and goal expressions that enables the definition of semantic interfaces and the evaluation of liveness properties. The same mechanisms also enable component reuse. We discuss how UML 2.0 can support the modeling of both the services and the desired properties. The approach is illustrated with telephony services.

ALIGNING UML 2.0 STATE MACHINES AND TEMPORAL LOGIC FOR THE EFFICIENT EXECUTION OF SERVICES

In our service engineering approach, services are specified by UML 2.0 collaborations and activities, focusing on the interactions between cooperating entities To execute services, however, we need precise behavioral descriptions of physical system components modeling how a component contributes to a service For these descriptions we use the concept of state machines which form a suitable input for our existing code generators that produce efficiently executable programs From the engineering viewpoint, the gap between the collaborations and the components will be covered by UML model transformations To ensure the correctness of these transformations, we use the compositional Temporal Logic of Actions (cTLA) which enables us to reason about service specifications and their refinement formally In this paper, we focus on the execution of services By outlining an UML profile, we describe which form the descriptions of the components should have to be efficiently executable To guarantee the correctness of the design process, we further introduce the cTLA specification style cTLA/e which is behaviorally equivalent with the UML 2.0 state machines used as code generator input In this way, we bridge the gap between UML for modeling and design, cTLA specifications used for reasoning, and the efficient execution of services, so that we can prove important properties formally.

Using UML 2.0 collaborations for compositional service specification

Collaborations and collaboration uses are features new to UML 2.0. They possess many properties that support rapid and compositional service engineering. The notion of collaboration corresponds well with the notion of a service, and it seems promising to use them for service specification. We present an approach where collaborations are used to specify services, and show how collaborations enable high level feature composition by means of collaboration uses. We also show how service goals can be combined with behavior descriptions of collaborations to form what we call semantic interfaces. Semantic interfaces can be used to ensure compatibility when binding roles to classes and when composing systems from components. Various ways to compose collaboration behaviors are outlined and illustrated with telephony services.

Realizability of Collaboration-based Service Specifications

This paper is concerned with compositional specification of services using UML 2 collaborations, activity and interaction diagrams. It addresses the problem of realizability: given a global specification, can we construct a set of communicating state machines whose joint behavior is precisely the specified one? We approach the problem by looking at how collaboration behaviors may be composed using UML activity diagrams. We classify realizability problems from the point of view of each composition operator, and discuss their nature and possible solutions. This brings a new look at already known problems: we show that given some conditions, some problems can already be detected at an abstract collaboration level, without needing to look into detailed interactions.

ICT convergence: modeling issues

Even though ICT convergence is a well-established and a-dopted concept, there is no consensus about the underlying software engineering approach to convergent ICT systems. Telecom engineers and software engineers traditionally use different approaches when developing services and applications. A main question is whether or not the differences are justified and should be maintained in the context of convergence? In this paper, we seek to answer this question by analyzing the different nature of the telecom domain and the computing domain. We identify a few fundamental differences that must be bridged when making convergent systems and we investigate how UML can be used as an enabler to build such bridges.

Synthesizing components with sessions from collaboration-oriented service specifications

A fundamental problem in the area of service engineering is the so-called cross-cutting nature of services, i.e., that service behavior results from a collaboration of partial component behaviors. We present an approach for model-based service engineering, in which system component models are derived automatically from collaboration models. These are specifications of sub-services incorporating both the local behavior of the components and the necessary inter-component communication. The collaborations are expressed in a compact and self-contained way by UML collaborations and activities. The UML activities can express service compositions precisely, so that components may be derived automatically by means of a model transformation. In this paper, we focus on the important issue of how to coordinate and compose collaborations that are executed with several sessions at the same time. We introduce an extension to activities for session selection. Moreover, we explain how this composition is mapped onto the components and how it can be translated into executable code.

Towards a Plug and Play Architecture for Telecommunications

This paper presents an architecture specified within the project “Plug-and-play for Network and Teleservice Components” supported by The Norwegian Research Council. The hardware and software parts, as well as complete network elements that constitute a communication system, shall have the ability to configure themselves when installed into a network and then to provide services according to their own capabilities, the service repertoire and the operating policies of the system.

A collaboration-based approach to service specification and detection of implied scenarios

Methods for service specification should be simple and intuitive. At the same time they should be precise and allow early validations to be performed, in order to detect inconsistencies as early as possible in the service development cycle. In this paper we present a service specification approach based on UML 2.0 collaborations. It aims to be a constructive approach, rather than a corrective one, as it is intended to promote understanding and help reducing the number of specification errors. We also address the detection of implied scenarios from collaboration-based service specifications, and propose an approach that limits the state explosion problem. This is possible since the detection analysis is modular and it is performed at a high-levelof abstraction.

Formalizing collaboration goal sequences for service choreography

Methods for service specification should be simple and intuitive. At the same time they should be precise and allow early validation and detection of inconsistencies. UML 2.0 collaborations enable a systematic and structured way to provide overview of distributed services, and decompose cross-cutting service behaviour into features and interfaces by means of collaboration-uses. To fully take advantage of the possibilities thus opened, a way to compose (i.e. choreograph) the joint collaboration behaviour is needed. So-called collaboration goal sequences have been introduced for this purpose. They describe the behavioural composition of collaboration-uses (modeling interface behaviour and features) within a composite collaboration. In this paper we propose a formal semantics for collaboration goal sequences by means of hierarchical coloured Petri-nets (HCPNs). We then show how tools available for HCPNs can be used to automatically analyse goal sequences in order to detect implied scenarios.

Towards a framework of authentication and authorization patterns for ensuring availability in service composition

Securing availability of applications and services is increasingly important for provisioning services in todays and future networks and systems. For fulfilling user expectations, availability depends more and more on the characteristics and requirements of the services themselves and the different requirements of certain users. In order to address service availability, we see availability as a composite notion consisting of the ability to ensure access for authorized users only, and the property of being on hand and useable when needed. Service composition is an approach to incremental service development contributing to rapid service design and development. This paper presents a set of authentication and authorization patterns addressing the aspect of ensuring access to authorized users only in service composition. We provide a framework and classification of these patterns, and we demonstrate how the patterns can be composed with services using a policy-driven approach.Securing availability of applications and services is increasingly important for provisioning services in todays and future networks and systems. For fulfilling user expectations, availability depends more and more on the characteristics and requirements of the services themselves and the different requirements of certain users. In order to address service availability, we see availability as a composite notion consisting of the ability to ensure access for authorized users only, and the property of being on hand and useable when needed. Service composition is an approach to incremental service development contributing to rapid service design and development. This paper presents a set of authentication and authorization patterns addressing the aspect of ensuring access to authorized users only in service composition. We provide a framework and classification of these patterns, and we demonstrate how the patterns can be composed with services using a policy-driven approach.