Increasingly, digital libraries are being defined that collect pointers to World-Wide Web based resources rather than hold the resources themselves. Maintaining these collections is challenging due to distributed document ownership and high fluidity. Typically a collection's maintainer has to assess the relevance of changes with little system aid. In this paper, we describe the Walden's Paths Path Manager, which assists a maintainer in discovering when relevant changes occur to linked resources. The approach and system design was informed by a study of how humans perceive changes of Web pages. The study indicated that structural changes are key in determining the overall change and that presentation changes are considered irrelevant.

When reflecting on information, spatial hypermedia users express their understanding of the information's structure visually. In order to facilitate this process, spatial hypermedia uses spatial parsers that enable systems to infer the structure of information based on the implicit relationships between components of the representation. This paper describes the two main purposes of spatial parsers in spatial hypermedia systems and how particular parsing approaches and features influence their effectiveness and responsiveness. An alternative approach that provides better support for ambiguity and adaptability is instantiated in FLAPS, an adaptive spatial parser that uses fuzzy-logic in order to infer the implicit structure of spatial hypermedia. The comparison of FLAPS to other parsers reveals benefits of supporting ambiguous structures by computing multiple possible interpretations and identifies limitations that provide goals for future spatial parsers.

Medical information delivery for users with different levels of expertise will be required for the manned mission to Mars due to limited potential for communication with Earth. The Mars Medical Assistant (MMA) uses a combination of user, situation, and task models to create virtual hypertext structures by piecing together medical "information components." Information components are chosen based on the semantic content and the cognitive characteristics of the component's media type. The medical assistant currently supports three tasks: 1) describing medical procedures, 2) aiding diagnosis, and 3) providing information on health concerns. Conflicting suggestions from the three models need to be resolved. Tradeoffs in the model representations and conflict resolution strategies are being explored in the context of MMA.

Web pages such as news and shopping sites often use modular layouts. When used effectively this practice allows authors to present clearly large amounts of information in a single page. However, while sighted people can visually parse and understand these complex layouts in seconds, current assistive technologies such as screen readers cannot. This puts visually impaired users at a great disadvantage. In order to design better assistive technologies, we conducted a study of how people interpret modular layouts of news and shopping Web pages. The study revealed that when the layout complexity increases, the interpretation process gets longer and the reading gets more varied. Also, before looking at the main content, users first frame the Web page by looking for familiar structural elements that can be used as references and entry points. These elements include navigational bars, search boxes, and ads. This implies that assistive technologies can reduce the time required to frame the pages if they help users identify reference points and entry points.

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