Structuring specification in Z to build a unifying framework for hypertext systems

A report is given on work undertaken to produce a structured specification in Z of a model which aims to capture the essential abstractions of hypertext systems. The specification is presented in part and the potential value of this specification to the hypertext community is explored and discussed. We argue that this specification provides a framework for hypertext systems in that it provides: explicit and unambiguous definitions of hypertext terms, an explicit environment for the presentation, comparison and evaluation of hypertext systems and a foundation for future research and development in the field. Although there are many formal reference models of hypertext, we have found Z expressive enough to allow a unified account of a system and its operations. Our model does not restrict the specifier to any particular design, but provides a mathematical framework within which different models may be compared. Further, we were able to structure the specification in order that the model could be described initially at the highest level of abstraction with complexity added at increasingly lower levels of abstraction. This structured specification allows the functionality of hypertext systems to be considered at different levels of granularity which, we argue, gives rise to a well-defined robust model and a beneficial environment within which to reason about hypertext design. The use of this model in presenting and comparing existing models, as well as its use in developing a new hypertext learning model, is briefly discussed.