Language support for service-level agreements for application-service provision

My thesis is that practical language support can be provided for Service-Level Agreements (SLAs) for Application-Service Provision (ASP), which is better than that provided by pre-existing languages in that: it provides greater assistance in expressing conditions that mitigate the risks inherent in ASP; and disputes related to agreements expressed in this manner may be more easily resolved in so as to respect the original intent of the parties. I support this thesis by establishing requirements for SLAs for ASP based on an account of a typical ASP infrastructure and business model. These identify the particular risks inherent in ASP, permit comparisons between ASP SLA languages, and guide the development of an abstract, extensible, domain-specific language, SLAng. SLAng is defined using a meta-modelling approach that allows a high degree of precision in the specification of its semantics, traceability from SLA to language specification, and the testing of the language and SLAs to ensure they capture the original intent of the parties. SLAng supports the expression of mutually-monitorable SLAs, for which the determination of compliance depends only on events visible to both client and provider of the service. I demonstrate that such SLAs are the most monitorable possible in a typical ASP scenario, given current monitoring technology, and describe an approximately-monitorable constraint on the accuracy of evidence used to administer such SLAs. SLAng is shown to be of practical use in a case study, evaluated against the original requirements, and compared with pre-existing languages. The evaluation of SLAng is enhanced using metrics developed to assist in assessing the contribution of a domain-specific language specification to encoding the meaning of statements in that language

Resilience-Building Technologies: State of Knowledge -- ReSIST NoE Deliverable D12

This document is the first product of work package WP2, "Resilience-building and -scaling technologies", in the programme of jointly executed research (JER) of the ReSIST Network of Excellenc

Quality assessment of service providers in a conformance-centric Service Oriented Architecture

In a Service Oriented Architecture (SOA), the goal of consumers is to discover and use services which lead to them experiencing the highest quality, such that their expectations and needs are satisfied. In supporting this discovery, quality assessment tools are required to establish the degree to which these expectations will be met by specific services. Traditional approaches to quality assessment in SOA assume that providers and consumers of services will adopt a performance-centric view of quality, which assumes that consumers will be most satisfied when they receive the highest absolute performance. However, adopting this approach does not consider the subjective nature of quality and will not necessarily lead to consumers receiving services that meet their individual needs. By using existing approaches to quality assessment that assume a consumer's primary goal as being optimisation of performance, consumers in SOA are currently unable to effectively identify and engage with providers who deliver services that will best meet their needs. Developing approaches to assessment that adopt a more conformance-centric view of quality (where it is assumed that consumers are most satisfied when a service meets, but not necessarily exceeds, their individual expectations) is a challenge that must be addressed if consumers are to effectively adopt SOA as a means of accessing services. In addressing the above challenge, this thesis develops a conformance-centric model of an SOA in which conformance is taken to be the primary goal of consumers. This model is holistic, in that it considers consumers, providers and assessment services and their relationship; and novel in that it proposes a set of rational provider behaviours that would be adopted in using a conformance-centric view of quality. Adopting such conformance-centric behaviour leads to observable and predictable patterns in the performance of the services offered by providers, due to the relationship that exists between the level of service delivered by the service and the expectation of the consumer. In order to support consumers in the discovery of high quality services, quality assessment tools must be able to effectively assess past performance information about services, and use this as a prediction of future performance. In supporting consumers within a conformance-centric SOA, this thesis proposes and evaluates a new set of approaches to quality assessment which make use of the patterns in provider behaviour described above. The approaches developed are non-trivial – using a selection of adapted pattern classification and other statistical techniques to infer the behaviour of individual services at run-time and calculating a numerical measure of confidence for each result that can be used by consumers to combine assessment information with other evidence. The quality assessment approaches are evaluated within a software implementation of a conformance-centric SOA, whereby they are shown to lead to consumers experiencing higher quality than with existing performance-centric approaches. By introducing conformance-centric principles into existing real-world SOA, consumers will be able to evaluate and engage with providers that offer services that have been differentiated based on consumer expectation. The benefits of such capability over the current state-of-the-art in SOA are twofold. Firstly, individual consumers will receive higher quality services, and therefore will increase the likelihood of their needs being effectively satisfied. Secondly, the availability of assessment tools which acknowledge the conformance-centric nature of consumers will encourage providers to offer a range of services for consumers with varying expectation, rather than simply offering a single service that aims to delivery maximum performance. This recognition will allow providers to use their resources more efficiently, leading to reduced costs and increased profitability. Such benefits can only be realised by adopting a conformance-centric view of quality across the SOA and by providing assessment services that operate effectively in such environments. This thesis proposes, develops and evaluates models and approaches that enable the achievement of this goal

Monitoring middleware for distributed applications

With growing maturity Internet services are proving integral to the provision of computer services. To provide consistent end-user experiences these services are increasingly augmented with some notion of 'Quality-of-Service' (QoS), which typically requires the management of computing resources to maintain a predictable level of service performance. It is difficult to guarantee consistent servIce provision In dynamic and open environments such as the Internet. However service monitoring can be used to inform compensatory actions by collecting meaningful service performance data from strategic points in an active service environment. Due to the unpredictable nature of the Internet distributed monitoring mechanisms face challenges with respect to the various communication protocols, application languages, and monitoring requirements associated with a service environment. With the growing popularity of Internet services creation of monitoring solutions on a per- service basis becomes time-consuming and misses opportunities to re-use existing logic. Ideally monitoring solutions would be domain-agnostic, automatically generated and automatically deployed. This thesis progresses these ambitions by providing a generic, distributed monitoring and evaluation framework based on Metric Collector (MeCo) components. These components can transparently gather measurement data across a range of service technologies as used within E-Commerce service environments. MeCo components form part of a framework which can interpret Service Level Agreements (SLAs) to automatically provide tailored service monitoring. The evaluation paradigms of the Meeo Framework are re-appropriated for use in Distributed Virtual Environments (DYEs). Quantifiable QoS requirements are established for Interest Management mechanisms (which limit message production based on object localities within a DYE). These are then incorporated into a DVE Simulator application. This application allows DYE application developers to evaluate Interest Management configurations for their suitability. Extensions to the DVE Simulator are exhibited in the Evolutionary Optimisation Simulator (EOS), which provides automated optimisation capabilities for DVE configurations through utilisation of genetic algorithm techniques.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Corrosion and Degradation of Materials

Studies on the corrosion and degradation of materials play a decisive role in the novel design and development of corrosion-resistant materials, the selection of materials used in harsh environments in designed lifespans, the invention of corrosion control methods and procedures (e.g., coatings, inhibitors), and the safety assessment and prediction of materials (i.e., modelling). These studies cover a wide range of research fields, including the calculation of thermodynamics, the characterization of microstructures, the investigation of mechanical and corrosion properties, the creation of corrosion coatings or inhibitors, and the establishment of corrosion modelling. This Special Issue is devoted to these types of studies, which facilitate the understanding of the corrosion fundamentals of materials in service, the development of corrosion coatings or methods, improving their durability, and eventually decreasing corrosion loss

Conception et mise en oeuvre d'une plate-forme pour la sûreté de fonctionnement des services Web

Les Services Web (SW) constituent la technologie de base pour le développement d'Architectures Orientées Services (AOS). Ces architectures, de plus en plus répandues sur le Net, permettent de mettre en place des applications semi-critiques à échelle planétaire. Elles se basent sur la notion de relation de "service" formalisée par un contrat qui unit le client et le prestataire de services. Dans ce type d'applications, les développeurs d'applications orientées services regardent les Services Web comme des COTS (Component Off-The Shell) et ignorent donc leurs implémentations et leurs comportements en présence de fautes. Dans ce but, cette thèse introduit, dans ce nouveau contexte, la notion de « connecteurs spécifiques de tolérance aux fautes » (SFTC – Specific Fault Tolerance Connectors) capable d'implémenter des applications sûres de fonctionnement à partir de Services Web supposés non-fiables. Composants logiciels insérés entre les clients et les prestataires, les SFTC implémentent des filtres et différentes techniques de détection d'erreurs ainsi que des mécanismes de recouvrement qui sont déclenchés quand les Services Web ne satisfont plus les caractéristiques de sûreté demandées. L'originalité de cette approche est d'utilisé une particularité intéressante du Web qui est la redondance inhérente des services qui s'y trouvent. Cette propriété a permis de définir le concept de Services Web Abstrait (SWA) et de mettre en place des stratégies de recouvrement à l'aide de services équivalents. Ainsi, les « connecteurs » et les « SWA », introduits dans les architectures orientées services, fournissent une approche plus adaptable pour permettre, à des mécanismes de sûreté, d'être définis au cas par cas pour une utilisation donnée du Service Web et d'être modifiés selon la criticité de l'application. Ainsi, mes travaux de recherches ont permis de fournir aux développeurs d'Architectures Orientées Services : 1) le langage nommé DeWeL pour décrire les caractéristiques de sûreté de fonctionnement du connecteur. Ce langage dédié à la réalisation de connecteur impose de fortes restrictions inspirées du monde des logiciels critiques du ferroviaire et de l'avionique afin de diminuer de façon drastique des fautes de développement. 2) l'infrastructure IWSD pour dynamiquement contrôler et exécuter les connecteurs dans des applications critiques. Cette plateforme, réalisé en mode duplex pour tolérer les fautes matérielles et logicielles, permet d'exécuter de façon sûres les connecteurs crées et d'obtenir également des informations sur le caractère non-fonctionnel et opérationnel des Services Web ciblés. Ces informations sont capitales pour permettre aux développeurs de connecteurs d'affiner leurs actions de tolérances aux fautes pour l'application ciblée. Environ deux cents connecteurs ont été implémentés afin de réaliser des tests sur la performance et la robustesse du langage et de la plate-forme permettant ainsi de valider cette approche capable de déployer des applications orientées services semi-critiques tolérant les fautes à l'aide de SWA. ABSTRACT : Web Services (WS) technology is the basis for the development of Service Oriented Architectures (SOA). These architectures are increasingly widespread on the Net and enable developers to implement semi-critical planetary applications. Such applications are based on the notion of service and its attached contract. The contract links a client and a service provider. In this kind of applications, application developers look at Web Services as COTS (Commercial Off-The- Shelf) components, consequently they ignore their implementation and their behaviour in the presence of faults. The thesis proposes the notion of Specific Fault Tolerance Connectors (SFTC) to implement dependable applications out of unreliable Web Services. The connectors intercept client-provider requests and implement filtering, error detection techniques (e.g. runtime assertions) together with recovery mechanisms that are triggered when the WS does not satisfy anymore the dependability specifications. The originality of this approach relies on using an interesting feature of the Web that is the inherent redundancy of services. To take advantage of this, we define the concept of Abstract Web Services (AWS) to implement recovery strategies using equivalent services. Thus, "connectors” and “AWS” allow dependability mechanisms to be defined on a case-by-case basis for a given WS usage and possibly dynamically changed according to the needs. Two specific techniques and tools have been designed and implemented to help developers of Services Oriented Architectures : 1) A domain specific language named DeWeL (DEpendable Web services Language) describing the dependability features of a connector. This language is devoted to the realization of connectors. It imposes strong restrictions enforced by standards for critical railway and avionics software in order to reduce software development faults. 2) A support infrastructure named IWSD (Infrastructure for Web Services Dependability) to dynamically manage and run connectors in real applications. This platform is implemented in duplex mode to tolerate crash faults and provides core services. In particular, it provides support to run connectors and get information on the non-functional and operational behaviour of the targeted Web Services. This information is essential to help developers of connector to adjust their fault-tolerance actions to specific application needs. Approximately two hundred connectors have been implemented in order to realize performance and robustness tests of the language and the platform. These experiments show the interest of our approach to deploy fault-tolerant service oriented applications using AW

Software: our quest for excellence. Honoring 50 years of software history, progress, and process

The Software Quality Forum was established by the Software Quality Assurance (SQA) Subcommittee, which serves as a technical advisory group on software engineering and quality initiatives and issues for DOE`s quality managers. The forum serves as an opportunity for all those involved in implementing SQA programs to meet and share ideas and concerns. Participation from managers, quality engineers, and software professionals provides an ideal environment for identifying and discussing issues and concerns. The interaction provided by the forum contributes to the realization of a shared goal--high quality software product. Topics include: testing, software measurement, software surety, software reliability, SQA practices, assessments, software process improvement, certification and licensing of software professionals, CASE tools, software project management, inspections, and management`s role in ensuring SQA. The bulk of this document consists of vugraphs. Selected papers have been indexed separately for inclusion in the Energy Science and Technology Database