The Trellis Hypertext Reference Model

Richard Furuta and P. David Stotts have developed a hypertext system, based on Petri Nets, called the Trellis System. The system implements their Trellis model of hypertext [SF89]. From the Trellis model they deduced a meta-model, which they called the Trellis hypertext reference model, abbreviated as r-model [FS90].

The r-model is separated into five logical levels, as shown in the figure below. Within each level one finds one or more representations of part or all of the hypertext. In contrast to the HAM (and the other reference models) the levels represent levels of abstraction, not components of the system. The levels may be grouped into three categories: abstract, concrete and visible, corresponding to the model of Shaw for printed documents [Shaw-80].

(You may click in any of the five regions to get an explanation of the corresponding levels Abstract Component Level, Abstract Hypertext Level, Concrete Context Level, Concrete Hypertext Level and Visible Hypertext Level.
Clicking on the image does not work in static or off-line versions of this course.)

In the figure the arcs indicate that a concept at a lower level is dependent on a concept at a higher level of abstraction.

In order to apply the r-model as a reference model components of actual hypertext systems need to be fitted into the r-model. This is complicated by the abstraction levels because different components can only be described at certain levels of the r-model. Stotts and Furuta have indicated how to model hypertext model structures, anchors, different flavors of links and dynamic content.

Some aspects of hypertext are deliberately excluded from the r-model. These include:

Abstract Component Level Abstract Hypertext Level Concrete Context Level Concrete Hypertext Level Visible Hypertext Level