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Back-end Requirements

The hypermedia engine would provide functionality such as linking, annotation, backtracking, filtering, and overviews on behalf of the back-end. The back-end should provide the following functionality:

Similar to Intermedia’s Link Engine and Bieber’s Hypermedia Engine, Sun’s Link Service offers an extensible protocol to create and maintain relationships between autonomous front-end applications [Pearl, 1989]. Similar to the approaches seen earlier, editing and storing of data objects is managed by independent applications which also provide some amount of front-end operations on links. The Link Service stores only the representations of the nodes rather than the nodes themselves. Thus, the definition and granularity of nodes are left to the individual applications. Also, the storage of node data is independent of the storage of link data.

The Link Service makes it easier for applications to add hypertext functionality by providing a simple protocol, a shared back-end or link server, a library, and utilities to manage the link database (See Figure 6.2). Applications communicate with the link server through the Link Service protocol. This service allows independent applications to integrate linking mechanisms into their standard functionality and become part of an extensible and open hypertext system. Existing text and graphics editors can be integrated into such a framework without any modifications. Due to the separation of node and link data, the Link Service does not provide version control, node content editors, concurrent multi-user access, or other forms of data integration.

An Architecture for Open Hypertext
Figure 6.2: Link Service – An Architecture for Open Hypertext [Pearl, 1989].

Some of the issues involved in developing such an open hypertext system include the following [Pearl, 1989]: