Design of Quality Aspects in Service Oriented Architecture through Service Level Agreements: The Streaming Case Study

The development of Service Oriented Architectures is a challenging task to achieve because of both functional and non-functional aspects which should be addressed. Quality requirements concerning the requested and provided services play a determinant role in this context. A low quality level of services at runtime may be of critical importance in their execution flow, thus there are requested mechanisms to monitor and enforce the quality levels of services directly and dynamically. The definition of Quality of Services should be performed explicitly and clearly in order to be used properly in any phase of the services negotiation and provision. Service Level Agreements offer an appropriate mechanism for the definition and negotiation of services in Service Oriented Architectures. They have the power of contracts through which requesters of services specify their expectations in functional and qualitative terms. The providers of services engage themselves to fulfill such requirements. Being available both at the requester and provider sides, the Service Level Agreements represent the appropriate mechanism through which quality requirements may be monitored and evaluated at runtime. However, only the specification of quality requirements does not ensure that the provisioning of services flows smoothly. Unexpected problems may occur at runtime. Therefore, further means to enforce the quality aspects are needed. In this context, runtime adaptivity is an enhanced solution to address and fulfill this goal. Adaptivity enables the architecture to monitor and perform changes during the execution of services (including the change of the service provider) in order to ensure the requested and expected qualities properties specified in the Service Level Agreements. This chapter gives a solution to design Service Oriented Architectures which defines and manages Service Level Agreements to enforce Quality of Services and achieves adaptivity at runtime. The validation of this proposed approach is performed through an actual case study in the context of the multimedia application domain.