The main motivation for the definition of this formal model is the lack of means to interchange and communicate between existing hypertext systems. Hypertext research is driven mostly by user interface and implementation considerations. Very few attempts have been made to provide a formal basis for the research field. David Lange chose the Vienna Development Method (VDM) [BJ82,Jones-86] because it supports the top-down development of software systems specified in a notion suitable for formal verification.
Like the Dexter model Lange's model emphasizes the data structure of hyperdocuments. Therefore Lange calls it a datamodel of hypertext. This datamodel defines nodes, links, network structures, etc. The model goes further than the Dexter model in looking inside the nodes of a hyperdocument to find slots, buttons and fields. The basic datamodel is then extended with features to become an object-oriented model for hypertext.
As a result of the focus on the data model the presentation of hypertext and the browsing semantics are excluded from the model. The applications should only operate on a hyperdocument through the specified operations and the data objects should not be aware of the applications and their semantics. By adding the aspects of persistence to the object-oriented model one obtains a model of an object-oriented database. In this way issues on distribution, version management and access control could be solved in the domain of object management systems.
One severe restriction in Lange's model is the strong emphasis on textual information. This makes it possible to give a more detailed description of the internal structure of nodes, but make the model ill-suited to describe hypermedia systems in general. Also, some of the detailed descriptions in the model reduce the generality of this model, even for pure (textual) hypertext systems.