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HDM - A Model for the Design of Hypertext Applications
Franca Garzotto, Paolo Paolinil

Dipartimento di Elet.tmnica, Politecnico di Milano, Piazza Lemardo da Vinci, 32, Mihno 20133, Italy

Daniel

Schwabe2

Department of Informatics, Pontificia Universidade Catdlica, R. M. de S. Vicente, 225 22453 Rio de Janeiro, Brazil

ABSTRACT
We present the latest developments of HDM, a designmodel for Hypertext Applications. The basic features of HDM are the representation of applications through several design primitives: typed entities composed of hierarchies of component different perspectives for each componen~ units corresponding to component-perspective pairs; bodies representing the actual content of the units; structural links, binding together components or sub-entities of thesame entity; typed application links, interconnecting components belonging to different entities; and a spccitlc browsing semantics based on anchors, as a way to activate many different link types from within a unit. The development of HDM is part of the HYTEA project, carried on by a European consortium, aiming at the development of a set of authoring tools for an “engineered development ofHypertext-Hypermedia applications. A HYTEA application is made by an HDM schema and an HDM Hyperbase (i.e., a set of instances). The basic HDM has already been shown to be translatable, either manually or through a compiler, into a nodeand-link model (“a la DEXTER model”); the translated application can be targeted on several implementation tools (i.e., standard Hypertext tools already available on themarket). HDM has already been used to develop a (small number) of applications, and to describe preexisting applications. These experiments have shown the need for improvements that are discussed in the papec aggregate entities; sharing of components; is-a relationships and inheritance between entity types; sharing of bodies; structured access and “guided tours”; use of active media (animationsand video-clips).

lE-mail:relett34@

imipoli.bitnet leave during 1990 (partially

2Daniel Schwabe developed this work while on sabbatical supported by CNPq-Brasil). E-maih schwabe@inf.puc-rio.br Hypertext ’91 Proceedings 313

December 1991

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INTRODUCTION

Many hypertext applications deal with very complex application domains (legislation, engineering, etc.), that may get even morecomplex when multinational, multilingual and cross-cultural aspects also must be considered. This is particularly true for corporate applications, where the complexity is increased with additional consistency demands arising from the different parts of the corporation and of its operating environment. Successful hypertext authors directly interconnect meaningful parts of the information base, toconvey natural way. The appropriate choice of which links to crucial design step. For this purpose, node-and-link level too low-level, being more oriented toward implementation only the most important and the overall meaning in a more include, and which to omit is a models [Hzdasz 90, Garg 88] are than toward design.

We are concerned with authoring-in-the-large: defining the topology of thehypertext. During the design of an application, authoring-in-the-large concerns are more important, as they will ultimately determine the navigation patterns available for readers. Authoring-in-the-small (i.e., filling in the contents of nodes and determining their appearance to readers) is also very important, but it is a different activity that we claim can (and should) be dealt with separately.This view is based on the belief that systematic and rational structural decisions about the hypertext should be made before the actual hypertext is ever written, so that coherent and expressive hypertext webs can be designedin instead of added-on. The extent of this top-down approach has not yet been determined, and many authors would disagree with such a strict top-down stance. Even though we...