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2.2 Link Engine/Hypermedia Engine/Link Service

Developers of Intermedia} were interested in developing a multiuser hypermedia framework whereby hypertext functionality could be handled at the system level – linking would be available for all participating applications [Haan et al., 1992]. They proposed “The IRIS Hypermedia Services” to provide an integrated desktop environment for hypermedia applications such as InterWord, InterDraw, InterVal, InterVideo, and InterPlay. These services contain the following components: Intermedia Layer, Link Client, and Link Server. These components are independent of both operating system and Graphical User Interface.

The documents themselves are stored as Unix files while the link and anchor data are stored in a DBMS. The Link Client, the Link Server, and the DBMS together form the Link Engine. The Intermedia Layer is responsible for all live data manipulation while the Link Engine is responsible for the storage and retrieval of link data. With such an approach Intermedia documents could be interchanged with KMS using the Dexter Interchange Format.

According to Intermedia researchers, following are the requirements to make hypermedia an integrated part of the computing environment:

  1. Integration of hypermedia into the desktop. The Link Engine must be integrated into the computing environment just as the file system is today. A higher level toolkit or an application programmer interface (API) must be provided for application developers to issue calls for hypermedia support.
  2. Hypermedia systems must provide multiple contexts or multiple webs in order to fully exploit hypertext linking across all applications.
  3. Hypermedia applications must support filtering and incremental query construction.
  4. Wide Area Hypermedia – Hypermedia functionality must be extended to support Wide Area Networks in addition to LANs.
  5. Building an integrated hypermedia environment is made easier with object-oriented techniques. Also, the most logical DBMS to use for storing link and anchor data would be an Object-Oriented Data Base Management System.
In order to provide an integrated desktop with full hypermedia functionality, Bieber has proposed a system-wide hypermedia engine based on the notion of a generalized hypermedia using bridge laws (see Section 2.5 about Dynamic Hypertext) [Bieber, 1993b]. This engine would bind independent back-end applications such as Decision Support Systems, Expert Systems, Databases and front-ends (interface-oriented applications such as word processors, graphics packages) through message-passing mechanisms. Bridge laws map the objects defined in the back-end such as models, variables, calculations to objects in the front-end such as nodes, links, and link markers.

Bieber has suggested front-end and back-end requirements for system-level approaches to hypermedia integration or client/engine cooperation.