Structuring Specication in Z to Build a Unifying Framework for Hypertext Systems

Abstract. A report is given on work undertaken to produce a struc-tured specication in Z of a model which aims to capture the essential abstractions of hypertext systems. The specication is presented in part and the potential value of this specication to the hypertext community is explored and discussed. We argue that this specication provides a framework for hypertext systems in that it provides: explicit and un-ambiguous denitions 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 eld. Although there are many formal reference models of hypertext, we have found Z expressive enough to allow a unied account of a system and its opera-tions. Our model does not restrict the specier to any particular design, but provides a mathematical framework within which dierent models may be compared. Further, we were able to structure the specication in order that the model could be described initially at the highest level of abstraction with complexity added at increasingly lower levels of ab-straction. This structured specication allows the functionality of hyper-text systems to be considered at dierent levels of granularity which, we argue, gives rise to a well-dened robust model and a benecial envi-ronment 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 brie y discussed.