Precise service level agreements

SLAng is an XML language for defining service level agreements, the part of a contract between the client and provider of an Internet service that describes the quality attributes that the service is required to possess. We define the semantics of SLAng precisely by modelling the syntax of the language in UML, then embedding the language model in an environmental model that describes the structure and behaviour of services. The presence of SLAng elements imposes behavioural constraints on service elements, and the precise definition of these constraints using OCL constitutes the semantic description of the language. We use the semantics to define a notion of SLA compatibility, and an extension to UML that enables the modelling of service situations as a precursor to analysis, implementation and provisioning activities

Service discovery and negotiation with COWS

To provide formal foundations to current (web) services technologies, we put forward using COWS, a process calculus for specifying, combining and analysing services, as a uniform formalism for modelling all the relevant phases of the life cycle of service-oriented applications, such as publication, discovery, negotiation, deployment and execution. In this paper, we show that constraints and operations on them can be smoothly incorporated in COWS, and propose a disciplined way to model multisets of constraints and to manipulate them through appropriate interaction protocols. Therefore, we demonstrate that also QoS requirement specifications and SLA achievements, and the phases of dynamic service discovery and negotiation can be comfortably modelled in COWS. We illustrate our approach through a scenario for a service-based web hosting provider

1 A Survey on Service Quality Description

Quality of service (QoS) can be a critical element for achieving the business goals of a service provider, for the acceptance of a service by the user, or for guaranteeing service characteristics in a composition of services, where a service is defined as either a software or a software-support (i.e., infrastructural) service which is available on any type of network or electronic channel. The goal of this article is to compare the approaches to QoS description in the literature, where several models and metamodels are included. consider a large spectrum of models and metamodels to describe service quality, ranging from ontological approaches to define quality measures, metrics, and dimensions, to metamodels enabling the specification of quality-based service requirements and capabilities as well as of SLAs (Service-Level Agreements) and SLA templates for service provisioning. Our survey is performed by inspecting the characteristics of the available approaches to reveal which are the consolidated ones and which are the ones specific to given aspects and to analyze where the need for further research and investigation lies. The approaches here illustrated have been selected based on a systematic review of conference proceedings and journals spanning various research areas in compute

A methodology for automated service level agreement compliance prediction

PhD ThesisService Level Agreement (SLA) specification languages express monitorable contracts between service providers and consumers. It is of interest to determine if predictive models can be derived for SLAs expressed in such languages, if possible in a fashion that is as automated as possible. Assuming that the service developer or user uses some SLA specification languages during the service development or deployment process,the Service level agreement Compliance Prediction(SlaCP) methodology is proposed as a general engineering methodology for predicting SLA compliance.This methodology helps contractual parties to assess the probability of SLA compliance,as automatically as is feasible,by mapping an existing SLA on a stochastic model of the service and using existing numerical solution algorithms or discrete event simulation to solve the model.The SlaCP methodology is generic, but the methodology is mostly described,in this thesis,assuming the use of the Web Service Level Agreement(WSLA)and the Stochastic Discrete Event Systems (SDES)formalism.The approach taken in this methodology is firstly to associate formal semantics with WSLA elements in order to be understood mathematically precise.Then,a five-step mapping process between the source and the target formalisms is conducted.These steps include:mapping into model primitives,reward metrics,expressions for functions of the semetrics,the time at which the prediction occurs,and the ultimate probability of SLA compliance.The proposed methodology is implemented in a software tool that automates most of its steps using Mobius and SPNP.The methodology is evaluated using a case study which shows the methodology’s feasibility and limitations in both theoretical and practical terms.Tishreen University, Ministry of Higher Education in Syri

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

Towards a contract-based interoperation model

Web Services-based solutions for interoperating processes are considered to be one of the most promising technologies for achieving truly interoperable functioning in open environments. In the last three years, the specification in particular of agreements between resource / service providers and consumers, as well as protocols for their negotiation have been proposed as a possible solution for managing the resulting computing systems. In this report, the state of the art in the area of contract-based web service applications is closely studied, identifying current limitations and possibilities. On the basis of this analysis, a general model for contract specification, negotiation, agreement, execution and management is introduced. Such a model has broad applicability both in electronic business integration and distributed knowledge management systems for decision support. Initial work presented here was completed in September 2005 and is published here as background for the European Commission funded project IST CONTRACT http://www.ist-contract.org/.Postprint (published version

SLA-driven dynamic cloud resource management

As the size and complexity of Cloud systems increase, the manual management of these solutions becomes a challenging issue as more personnel, resources and expertise are needed. Service Level Agreement (SLA)- aware autonomic cloud solutions enable managing large scale infrastructure management meanwhile supporting multiple dynamic requirement from users. This paper contributes to these topics by the introduction of Cloudcompaas, a SLA-aware PaaS Cloud platform that manages the complete resource lifecycle. This platform features an extension of the SLA specification WS-Agreement, tailored to the specific needs of Cloud Computing. In particular, Cloudcompaas enables Cloud providers with a generic SLA model to deal with higher-level metrics, closer to end-user perception, and with flexible composition of the requirements of multiple actors in the computational scene. Moreover, Cloudcompaas provides a framework for general Cloud computing applications that could be dynamically adapted to correct the QoS violations by using the elasticity features of Cloud infrastructures. The effectiveness of this solution is demonstrated in this paper through a simulation that considers several realistic workload profiles, where Cloudcompaas achieves minimum cost and maximum efficiency, under highly heterogeneous utilization patterns. © 2013 Elsevier B.V. All rights reserved.This work has been developed under the support of the program Formacion de Personal Investigador de Caracter Predoctoral grant number BFPI/2009/103, from the Conselleria d'Educacio of the Generalitat Valenciana. Also, the authors wish to thank the financial support received from The Spanish Ministry of Education and Science to develop the project 'CodeCloud', with reference TIN2010-17804.García García, A.; Blanquer Espert, I.; Hernández García, V. (2014). SLA-driven dynamic cloud resource management. Future Generation Computer Systems. 31:1-11. https://doi.org/10.1016/j.future.2013.10.005S1113