Links are the key element for changing a text into a hypertext, and yet the WWW provides limited linking facilities. Modelled on Open Hypermedi

Carr, Les A.

Davis, Hugh C.

DeRoure, David C.

Hall, Wendy

English

Southampton (e-Prints Soton)

iImplementing an Open Link Service for the World-Wide WebL. A. Carr1, D. De Roure, W. Hall & G. HillMultimedia Research Group,University of Southampton, SO17 1BJ, UK                                                1 Email address: lac@ecs.soton.ac.ukiiABSTRACTLinks are the key element for changing a text into a hypertext, and yet the WWW provideslimited linking facilities. Modelled on Open Hypermedia research the Distributed Link Serviceprovides an independent system of link services for the World-Wide Web and allows authors tocreate configurable navigation pathways for collections of WWW resources. This is achieved byadding links to documents as they are delivered from  a WWW server, and by allowing theusers to choose the sets of links that they will see  according to their interests. This paperdescribes the development of the link service, the facilities that it adds for users of the WWWand its specific use in an Electronic Libraries project.Key words: Links, hypertext, open hypermedia, link services, authoring, HTTPproxies.11In other words, users have prior experience with a reading model in which they evaluate thecontent before they evaluate the links, whereas the WWW and most other hypertextenvironments provide an environment in which the user is repeatedly interrupted, stacking upunfinished document contexts to be returned to later. Although the hypertext environment itselfdoes not force the user to switch contexts to the linked material, the lack of support for any otherbrowsing protocol often makes it the line of least resistance.In computing terms, the hypertext browser imposes a stack-based document evaluation modalityonto the user, replacing a natural queue-based information processing methodology. This stack-based approach is impractical in the real world because of the significant time taken to changedocument contexts when compared to the Web.As well as providing mechanisms for controlling the prioritizing and presentation of links, theDLS supplies a mechanism to help control the link following process, making it more like thereal-world experience described above. It does this by providing an auxiliary "navigation plannerwindow" adjacent to the users’ browser window such that users can drag link anchors from thebrowser window onto the planner window, where they are displayed as icons. The icons can bemoved around the window, clustered together according to the user’s own informal classificationscheme and subsequently double-clicked to make the browser display the relevant Webdocument.                            Figure 5: DLS link access auxiliary windowAs such an electronic notepad has been created for jotting down interesting places to visit (aspeculative bookmark list). However, a secondary function of the notepad is to pre-fetch thereferenced documents while the user finishes browsing the main document, so that the readerreally does get instantaneous access when the follow-up texts are examined. In fact, thereferenced URL and all embedded data should be fetched, so that documents containing framesor images can display without delay.A further function of the navigation notepad is to help the user to put the process of linkfollowing into perspective by explicitly recording the context in which the current document andits linked items are being read. This can be particularly helpful since reading is done not in anintellectual vacuum, but as part of a process of writing, of note taking and of goals and strategiesfor creating other documents.15quickly describe and catalogue WWW resources in a way that allows an automated process toproduce sets of links to those resources.A significant practical shortcoming of the DLS is the requirement to retrieve and apply links tothe document while it is being delivered to the user. Any delay in the processing of the linkstherefore means that the user has to wait for the document. Although this has not proved to be asignificant problem for explicit databases of links, the more complicated processing required forcitation linking requires certain trade-offs to achieve the response times that WWW users expect.Furthermore, any kind of on-the-fly linking in the semantic domain (links between concepts)rather than in the purely lexical domain (links on text features) would slow the delivery of thedocument beyond the limits of acceptability. Therefore a new agent-style interface is beingdesigned for the link service, so that collections of links can be offered to the user as they arediscovered by various independent link processing modules all acting asynchronously. It is hopedthat this will allow the WWW to deal with the inherently abstract connections between textsmentioned in the introduction, rather than the point-to-point ‘jumps’ which it has allowed thusfar.ACKNOWLEDGEMENTSThe work on PDF linking was carried out by the Electronic Publishing Research group atNottingham University as part of the Open Journals project, JISC grant ELP2/35 from theElectronic Libraries program.BIBLIOGRAPHYAdler, S., A. Berglund, J. Clark, I. Cseri, P. Grosso, J. Marsh, G. Nicol, J. Paoli, D. Schach, H.S.Thompson and C. Wilson (1997), “A Proposal for Extensible Style Language (XSL),”Note,World Wide Web Consortium, MIT, 545 Technology Square, Cambridge, MA <URL:http://www.w3.org/TR/NOTE-XSL.html>.Angerstein, P. (1996), Summary of the Document Style Semantics and Specification Language(DSSSL), International Standard 10179, International Standards Organization DocumentISO/IEC JTC1/SC18/WG8 N1427.Bernstein M. 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Implementing an Open Link Service for the World Wide Web

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Implementing an Open Link Service for the World Wide Web

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