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1 Introduction<br />

Non-Invasive Improvements to Hyperl<strong>in</strong>k<strong>in</strong>g with HTML<br />

Maria G. Pimentel<br />

Computer Science Dept.<br />

USP/São Carlos, Brazil<br />

mgp@icmsc.sc.usp.br<br />

John Buford<br />

Computer Science Dept.<br />

U.Mass Lowell, USA<br />

buford@cs.uml.edu<br />

HTML <strong>in</strong>herits from earlier hypertext both the l<strong>in</strong>k-node model for associat<strong>in</strong>g external documents, and the<br />

presentation and <strong>in</strong>teraction behaviour provided by HTML document browsers. HTML document navigation is<br />

by means of basic operations def<strong>in</strong>ed for hypertext: free choice of l<strong>in</strong>k selection complemented by<br />

backtrack<strong>in</strong>g, bookmarks and history mechanisms, to name a few.<br />

The simplicity of the HTML model, however, limits the l<strong>in</strong>k structure that can be associated with the<br />

underly<strong>in</strong>g document collection. To illustrate the problem, this paper presents some l<strong>in</strong>k<strong>in</strong>g structures well<br />

known from the previous hypertext systems and which are not supported <strong>in</strong> HTML. We then refer to<br />

experimental work <strong>in</strong> which these constructs are supported by Java applets without modify<strong>in</strong>g HTML.<br />

Due to space constra<strong>in</strong>ts, we omit a detailed review of the limitations of HTML l<strong>in</strong>ks <strong>in</strong> comparison with<br />

widely discussed second generation hypertext systems. A number of other researchers have discussed<br />

improvements to the l<strong>in</strong>k model of the web, <strong>in</strong>clud<strong>in</strong>g Maurer [ 94] [ Ladd 95] and [ Carr 96]. Many proposals<br />

require either changes to the current web architecture or extensions to the server such as l<strong>in</strong>k databases. The<br />

current discussion focuses on non-<strong>in</strong>vasive improvements; <strong>in</strong> the long term we believe that more extensive<br />

improvements to the exist<strong>in</strong>g HTML hyperl<strong>in</strong>k paradigm will be desirable.<br />

2 Alternative Hyperl<strong>in</strong>k<strong>in</strong>g<br />

Multi-end L<strong>in</strong>k. One <strong>in</strong>terest<strong>in</strong>g construct used <strong>in</strong> Intermedia [ Meyrowitz 86] was the l<strong>in</strong>k with multiple<br />

dest<strong>in</strong>ations, also known as fat l<strong>in</strong>k. The author could specify a source anchor with several dest<strong>in</strong>ations; at the<br />

time of selection, the user is presented with a pop-up menu list<strong>in</strong>g the possibilities and can choose between<br />

them. Another approach to deal with fat l<strong>in</strong>ks has been programmed by users of NoteCards: when the l<strong>in</strong>k is<br />

selected, one w<strong>in</strong>dow is opened for each of the dest<strong>in</strong>ations Halasz [ 1988].<br />

Pop-up L<strong>in</strong>k. A temporary pop-up l<strong>in</strong>k is such that, when its source anchor is activated, the correspond<strong>in</strong>g<br />

dest<strong>in</strong>ation anchor is displayed on top of the orig<strong>in</strong>al anchor (and its w<strong>in</strong>dow) for a limited period of time. This<br />

type of l<strong>in</strong>k was available <strong>in</strong> systems such as Apple's HyperCard and OWL's Guide. The temporary Pop-up l<strong>in</strong>k<br />

is as part of the HTML+ specification; however, current browsers do not support it.<br />

Preview<strong>in</strong>g the Dest<strong>in</strong>ation of a L<strong>in</strong>k. The preview<strong>in</strong>g of the contents of the dest<strong>in</strong>ation anchor was<br />

orig<strong>in</strong>ally used <strong>in</strong> HyperTies [ Shneiderman 87] as an alternative to the user not to move from the context<br />

conta<strong>in</strong><strong>in</strong>g the source anchor. When l<strong>in</strong>k traversal is <strong>in</strong>itiated, a resumé of the dest<strong>in</strong>ation anchor is displayed.<br />

Afterward, the user can choose whether to f<strong>in</strong>ish the selection. The resumé proposal has been expanded and<br />

generalized to allow cyclic access to <strong>in</strong><strong>format</strong>ion about the associated anchors Pimentel [ 94].<br />

3. Allow<strong>in</strong>g alternative hyperl<strong>in</strong>k<strong>in</strong>g <strong>in</strong> HTML documents

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