Hadez, a Framework for the Specification and Verification of Hypermedia Applications

Abstract

In recent years, several methodologies for the development of hypermedia applications have been proposed. These methodologies are, primarily, guidelines to be followed during the design process. They also indicate what deliverables should be created at each of their stages. These products are usually informally specified - in the sense that they do not have formal syntax nor formally defined semantics - and they are not required to pass validity tests. Hadez formally specifies the design of a hypermedia application, supports the verification of properties of the specification, and promotes the reuse of design. Hadez is an object-oriented specification language with formal syntax and semantics. Hadez is based on the formal specification languages Z and Z++, with extensions unique to hypermedia. It uses set theory and first order predicate logic. It divides the specification of a hypermedia application into three main parts: its conceptual schema, which describes the domain-specific data and its relationships; its structural schema, which describes how this data is combined and gathered into more complex entities, called composites; and the perspective schema, which uses Abstract Design Perspectives (artifacts unique to Hadez) to indicate how these composites are mapped to hyperpages, and how the user interacts with them. Hadez provides a formal framework in which properties of a specification can be specified and answered. The specification of an application should not constrain its implementation and, therefore, it is independent of the platform in which the application is to be presented. As a consequence, the same design can be instantiated into different applications, each for a different hypermedia platform. Hadez can be further extended with design patterns. Patterns enable reuse by capturing good solutions to well-known problems. Hadez characterizes patterns and makes their use readily available to the designer. Furthermore, Hadez is process independent, and is intended to be used with any of the main hypermedia design methodologies: EROM, HDM, OOHDM or RMM.