Glen Dobson

QoSOnt: a QoS ontology for service-centric systems

This paper reports on the development of QoSOnt: an ontology for quality of service (QoS). Particular focus is given to its application in the field of service-centric systems. QoSOnt is being developed to promote consensus on QoS concepts, by providing a model which is generic enough for reuse across multiple domains. As well as the structure of the ontology itself an example application currently in development - SQRM (service QoS requirements matcher) - is discussed. This application is used to highlight some of the advantages of the ontology including standardisation and the level of machine understanding of QoS specifications which can be achieved.

Towards Unified QoS/SLA Ontologies

This paper reports on work in progress to produce a unified quality of service (QoS) ontology. This ontology must be applicable to the main scenarios identified such as QoS-based Web services selection, QoS monitoring and QoS adaptation. An evaluation of existing research in the field of QoS and service level agreement (SLA) ontologies is presented. Many of the authors of these works are involved in the initiative. The aim of this evaluation is to identify the weaknesses and strengths of existing ontologies in order to decide which parts of each should form the basis of a unified ontology. Progress in the ontology engineering process is also presented

Using WS-BPEL to Implement Software Fault Tolerance for Web Services

One area of the Web services architecture yet to be standardised is that of fault tolerance for services. At the same time, WS-BPEL is moving from a de facto standard to an OASIS ratified standard for combining services into processes. This paper investigates the feasibility of using WS-BPEL as an implementation technique for fault tolerant Web services. The mapping of various fault tolerance patterns to WS-BPEL is presented. A prototype tool for combining service interfaces into a single facade and configuring fault tolerant mechanisms on a per-operation basis is also discussed. It is found that most fault tolerance patterns readily map onto WS-BPEL concepts, particularly when using the upcoming 2.0 version of the language. Evaluating and minimising the performance overheads involved in process execution is identified as a key future direction, as is working on the functionality and usability of the configuration tool

A Domain-Independent Ontology for Non-Functional Requirements

Despite considerable research on ontologies for representing requirements models (and metamodels), little progress has been made in using ontologies to represent non-functional requirements. Non-functional requirements define the overall qualities of the resulting system. Because they are restrictions on system services, non-functional requirements are often of critical importance, and functional requirements may need to be sacrificed to meet them. However, because of their diverse nature, non-functional requirements are often expressed in non-standard domain-specific ways. This paper describes a nonfunctional requirements ontology that can be used to structure and express constraints as part of quality of service specification. The approach is illustrated using a small case-study.

A Faceted Approach to Service Specification

Service-centric computing is developing and maturing rapidly as a paradigm for developing distributed systems. In recent years there has been a rapid growth in the number and types of processes being proposed to support aspects of SOC. Many of these processes require that services be modelled in a particular way and this puts great pressure on traditional notions of service specification, questioning the very nature of how services should be described for potential consumers. We present a technique for addressing this theoretical and practical bottleneck: faceted service specification. This allows different specifications to exist side-by-side if they are needed, yet places little obligation on the service provider to support specifications that are judged to be of little or no value. We show how faceted service specification is being used in the SeCSE project to support advanced service-centric system development activities.

Migrating to SOAs by Way of Hybrid Systems

A progressive-evolution strategy for migrating systems to service-oriented architectures should minimize the risk to investments in existing software systems while letting businesses exploit the benefits of services. In principle, hybrid systems combine services with nonservice elements. SOAs present a compelling vision for businesses. Conceptually, services bring together a layer of business functionality and a layer of technological implementation.

Ontology-aided Translation in the Comparison of Candidate Service Quality

In engineering service-centric systems, it is possible to receive early feedback on candidate services that best match requirements. This includes the possibility of comparing the quality (not just functionality) of candidate services. This paper concentrates on the assessment of service quality at the requirements stage. In doing so, it is found that there is a problem in reaching a common understanding between the parties involved - i.e. different service providers and requirements engineers may use different metrics, units, etc. We present an approach in which our requirements-based service discovery tool exploits an ontology-based quality specification mechanism. This simplifies the problem of reaching a common understanding of quality and allows translation where providers choose to specify quality differently.

OWL and OWL-S for Dependability-Explicit Service-Centric Computing

In this position paper an attempt is made to relate dependability-explicit computing to the semantic web. The machine understandable nature of the semantic web suggests a way to reconcile the increasingly autonomous nature of service-based systems with the need to verify that, once deployed, systems conform to a dependability specification.

Specifying and Constructing a Fault-Tolerant Composite Service

This paper proposes a means to specify the semantics of fault tolerant Web services at an abstract level using semantics adapted from queuing system theory. A framework that supports the implementation of specified fault-tolerance is also described. Based on our work, we show how the redundancy and diversity characteristics of a service-oriented system can be expressed and implemented in a Web-service application.

Disambiguating Availability Specification through the use of OWL

Many Quality of Service (QoS) languages exist. However, not only do few encompass dependability, none acknowledge the semantic complexity of the vocabulary they provide. This paper presents a Quality of Service ontology which provides not only an extensible syntax for expressing dependability, but also rich, well-defined semantics. These semantics avoid ambiguity and misunderstanding as well as facilitating translation where possible. To demonstrate these features, this paper examines in depth how to use our QoS ontology along with the built-in capabilities of the Web Ontology Language (OWL) to capture the semantics of availability.