Devise Hypermedia

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In 1992 researchers at the University of Aarhus, Denmark decided to build a new hypertext system based on the DexterReferenceModel, both to prove its validity and demonstrate its flaws. The result was the Devise Hypermedia (DHM) system, an open and extensible architecture based around an object-oriented database.

The major deviation from the DexterReferenceModel in DHM was the inclusion of DanglingLinks. The DHM team pointed out that this was a natural extension of the DexterReferenceModel, and had the advantages of allowing users to construct links incrementally, and enabling 'lazy' updating and garbage collection when nodes were deleted from the hypertext.

Another interesting aspect of the DHM project was the exploration of LinkDirectionality:

  1. Semantic direction: the direction of the semantic relationship between one endpoint and another, for example A ëSupportsí B.

  2. Creation direction: the order of creation of the endpoints of a link. The earlier endpoint becomes the source, and the later endpoint the target of the link.

  3. Traversal direction: the direction of traversal of a link, as defined by the link creator. The link can subsequently only be traversed in this direction, relying on a menu of ëback-linksí as a mechanism to traverse them in the opposite direction.

Although the DexterReferenceModel allows for the specification of LinkDirectionality, it does not explain which of these notions should actually be assumed. The DHM team specified that all links would be bi-directional at creation, but that the user could modify the directionality if they wished.

See Also:


Design issues for a Dexter-based hypermedia system
Kaj GrØnbÊk & Randall Trigg, CommunicationsOfTheAcm, 37(3), 40ñ49, 1994.

-- Last edited October 27, 2002

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