The Architecture of Hypertext Systems
A hypertext system is a complex piece of software, consisting of several
parts which serve a very different purpose. We can distinguish for instance
- the Presentation Level or user interface
- the Hypertext Abstract Machine, serving nodes and links
- the Database level, providing efficient storage and network access
The above division has been proposed by Campbell and Goodman in 1988
[CG88].
We provide five different views on the architecture of hypertext
systems. Since they give an abstract conceptual model of hypertext
systems they are often called Reference Models.
- The HAM or Hypertext Abstract Machine,
as described by Campbell and Goodman.
- The Trellis model, a reference model
by Stotts and Furuta.
- The Dexter model, a reference model by Halasz
and Schwartz, written in the specification language Z.
- The Formal Model by B. Lange, a reference
model written in the specification language VDM.
- The Tower Model, a more general object-oriented
model by De Bra, Houben and Kornatzky.
As these models describe the possible conceptual elements in hypertext
systems, no implementation exists for any of these models.
Some systems have implemented parts of the HAM and the Dexter model.
(Note that this is not surprising: more than 20 years after the invention
of the relational database model the major database systems still implement
only part of the concepts of that model.)
To test whether you have mastered the reference models you should complete
a short test on hypertext architecture.