Stotts & Furuta

Stotts and Furuta describe virtual structures as dynamic adaptation of hypertext structure.^{[Stotts & Furuta, 1991]} It involves collecting information from user interaction with a hypertext system, making inferences and decisions based on this information and creating appropriate physical changes in the document at appropriate times. Adaptation can occur at two levels - behavior of the document (timing of sequences, providing automated help, presenting collections in parallel or in sequence etc) and structure of the document (the way the nodes are linked).

According to Stotts and Furuta, a hypertext document can be considered to have two layers - a fixed underlying information structure that is created by the hypertext author and a flexible structure that is superimposed on the former and is tuned to each user's requirements. The flexible layer can be generated dynamically. The manner in which information is organized and presented can be altered without actually changing the information relation contained in the original links. This is similar to Bieber's concept of bridge laws which simply map an application's non-hypertext data to a hypertext interface without changing the underlying data. Thus, a document can change to adapt the needs and preferences of individual users, the author's original structure being retained. Such a dynamic adaptation technique has been implemented in the Petri-net based Trellis system developed by Stotts and Furuta.