We present a formal definition of the Trellis model of hypertext and describe an authoring and browsing prototype called αTrellis that is based on the model. The Trellis model not only represents the relationships that tie individual pieces of information together into a document (i.e., the adjacencies), but specifies the browsing semantics to be associated with the hypertext as well (i.e., the manner in which the information is to be visited and presented). The model is based on Petri nets, and is a generalization of existing directed graph-based forms of hypertext. The Petri net basis permits more powerful specification of what is to be displayed when a hypertext is browsed and permits application of previously developed Petri net analysis techniques to verify properties of the hypertext. A number of useful hypertext constructs, easily described in the Trellis model, are presented. These include the synchronization of simultaneous traversals of separate paths through a hypertext, the incorporation of access controls into a hypertext (i.e., specifying nodes that can be proven to be accessible only to certain classes of browsers), and construction of multiple specialized (tailored) versions from a single hypertext.

No abstract

We present a view of hyperdocuments in which each document encodes its own browsing semantics in its links. This requires a mental shift in how a hyperdocument is thought of abstractly. Instead of treating the links of a document as defining a static directed graph, they are thought of as defining an abstract program, termed the links-automaton of the document. A branching temporal logic notation, termed HTL*, is introduced for specifying properties a document should exhibit during browsing. An automated program verification technique called model checking is used to verify that browsing specifications in a subset of HTL* are met by the behavior defined in the links-automaton. We illustrate the generality of these techniques by applying them first to several Trellis documents and then to a Hyperties document.

No abstract

Digital libraries need to facilitate the use of digital information in a variety of settings. One approach to making information useful is to enable its application to situations unanticipated by the original author. Walden's Paths is designed to enable authors to collect, organize, and annotate information from on‐line collections for presentation to their readers. Experiences with the use of Walden's Paths in high‐school classrooms have identified four needs/issues: (1) better support for the gradual authoring of paths by teachers, (2) support for student authoring of paths including the ability for students to collaborate on paths, (3) more obvious distinction between content of the original source materials and that added by the path author, and (4) support for maintaining paths over an evolving set of source documents. These observed needs have driven the development of new versions of Walden's Paths. Additionally, the experiences with path authoring have led to a conceptualization of metadocuments, documents whose components include complete documents, as a general domain where issues of collaboration, intellectual property, and maintenance are decidedly different from traditional document publication.