Links in hypermedia
Lynda Hardman, Dick C. A. Bulterman, Guido van Rossum
Proceedings of the fifth ACM conference on Hypertext - HYPERTEXT '93
Taking the concept of a link from hypertext and adding to it the rich collection of information formats found in multimedia systems provides an extension to hypertext that is often called hypermedia. Unfortunately, the implicit assumptions under which hypertext links work do not extend well to time-based presentations that consist of a number of simultaneously active media items. It is not obvious where links should lead and there are no standard rules that indicate what should happen to other
... arts of the presentation that are active. This paper addresses the problems associated with links in hypermedia. In order to provide a solution, we introduce the notion of context for the source and the destination of a link. A context makes explicit which part of a presentation is affected when a link is followed from an anchor in the presentation. Given explicit source and destination contexts for a link, an author is able to state the desired presentation characteristics for following a link, including whether the presentation currently playing should continue playing or be replaced. We first give an intuitive description of contexts for links, then present a structure-based approach. We go on to describe the implementation of contexts in our hypermedia authoring system CMIFed. KEYWORDS Hypermedia links, context for links, structured multimedia, hypermedia presentation FOLLOWING LINKS: AN INTRODUCTION TO CONTEXTS What does it mean to follow a link in a hypermedia presentation? The combination of dynamic and static media into one presentation increases the choice of what can happen on following a link. In order to understand the options that are available, it is useful to differentiate the behaviour of links in the three cases: hypertext, multimedia and hypermedia (shown schematically in Fig. 1 -note that for simplicity composite nodes have been omitted from the figure). We discuss the three models briefly, looking at their notions of links and what happens on following a link. In conventional hypertext ( Fig. 1(a) ), the model of a link is clear [Hala90]: when a link is followed, one 'leaves' the information in the source node and 'goes to' the information in the destination node. The presentation details of what it means to 'leave' a node vary from system to system, but the two most common options are that the information in the source node is replaced (e.g. HyperCard 1.0 [Appl87]) or a new window for the destination information is created Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission.