Evaluation of run-time quality attributes for web services architecture

Web-services operate in a complex loosely coupled, stateless. distributed environment often crossing organisational boundaries and using inherently unreliable underlying communications, usually outside of the direct control of the service provider. The business goals are to provide agreed levels of service in a timely, cost effective, secure and reliable way. In order to achieve these goals it is necessary to devote effort to ensure that the run-time quality attribute requirements of security, performance and dependability are properly identified and considered as early as possible in the architecture design process. This paper examines a scenario-based evaluation method that can be used to evaluate these attributes. The Quality Attribute Workshop (QAW) is a technique to ensure that stakeholders identify, prioritise and refine scenarios to evaluate the quality requirements and suggest architectural approaches. We use the QAW to generate scenarios in a cases study of a web-services application.