A Z Specification for Reliability Requirements of a Service-based System

The utilization of a Web services based application depends not only on meeting its functional requirements but also its non-functional requirements. The nonfunctional requirements express the quality of service (QoS) expected from a system. The QoS describes the capability of the service to meet the requirements of its consumers. In the context of Web services, considerations of QoS are critical for a number of reasons. Reliability is among the important QoS requirements of such distributed components as it enhances confidence in the services provided. Although the importance of QoS requirements are well established, they are often ignored until the end of the development cycle. Reasons cited for this are that they are difficult to define and represent precisely, and relay on entities that may not be known at early stages. This articles aims to address the challenges of incorporating the QoS at an early stage of service development and represent it in a precise manner. To achieve this goal, this paper makes use of a process model to facilitate the incorporation of the QoS attributes and Z as the specification language for its formalism. Reliability is used to exemplify the process. The Z schemas have been checked for syntax and type using the Fuzz type checker.