g the course of a task. Many of these applications involve the collection, comprehension, 88 August 1995/Vol. 38, No. 8 COMMUNICATIONS OF THE ACM Catherine C. Marshall Frank M. Shipman III Spatial Hypertext: Designing for Change ypertext, 1 in its most general sense, allows content to appear in different contexts. The immediate setting in which readers encounter a specific segment of material then changes from reading to reading or from reader to reader. Authors collect and structure materials to reflect their own understanding or in anticipation of readers' possible interests, needs, or ability to comprehend the substrate of interrelated content. 1 We use the term hypertext broadly, to cover both textual and multimedia content. Node A Node A Node D Node E Node C Node B Node A and interpretation of diverse materials

Logical models of argument formalize commonsense reasoning while taking process and computation seriously. This survey discusses the main ideas which characterize different logical models of argument. It presents the formal features of a few main approaches to the modeling of argumentation. We trace the

In this paper, we report about the design, development, and implementation of the SEPIA cooperative hypermedia authoring environment. It provides results on the following aspects of SEPIA: persistent and shared data storage, hypermedia data model with composites, sophisticated and comprehensive authoring functionality, support for a new rhetoric and for cooperative work. We start by identifying the challenge of hypermedia authoring and production which serves as the driving force for our development. Using interacting problem spaces as the vehicle for modelling the dynamic aspects of authoring, we arrive at a set of requirements answered by the concept of "activity spaces". The design of coherent hyperdocuments is facilitated by our "construction kit". Furthermore, we describe the extensions and modifications necessary to support multiple authors with the cooperative version of SEPIA. The central issue of the paper is the system architecture and its implementation. We describe the basi...

rom the beginning, hypermedia application design has been driven primarily by technological innovations and constrained by technical feasibility. For the last few years, however, usability methods and results from human factors research have been gaining more influence [17]. Despite this trend toward user-oriented development procedures, issues of cognition and human information processing still are widely neglected and barely influence hypermedia design.

This paper discusses experiences and lessons learned from the design of an open hypermedia system, one that integrates applications and data not "owned " by the hypermedia. The Dexter Hypertext Reference Model [8] was used as the basis for the design. Though our experiences were generally positive, we found the model constraining in certain ways and underdeveloped in others. For instance, Dexter argues against dangling links, but we found several situations where permitting and supporting dangling links was advisable. In Dexter, the data objects making up a component's contents are encapsulated in the component; in practice, references to objects stored apart from the hypermedia structure should be allowed. We elaborate Dexter's notion of composite component to include composites that "contain " other components and composites with structured contents, among others. The paper also includes a critique of Dexter's notion of link directionality, proposes a distinction between marked and unmarked anchors, and discusses anchoring within a composite.

this paper, we give a vision of third- and fourth-generation hypermedia, and some direction for developers to implement them on the web---and indeed in other information systems

Hypertexts may be implicitly structured, based on either node content or context. In this paper, we examine implicit structures that rely on the interpretation of node’s spatial context. Hypertext authors and readers can perceive and understand these idiosyncratic structures, but, because they are implicit, they cannot be used by the system to support users ’ activities. We have explored spatially structured hypertext authored in three different systems, and have developed heuristic recognition algorithms based on the results of our analyses of the kinds of structures that people build. Our results indicate that (1) recognition of implicit structures in spatial hypertext is feasible, (2) interaction will be important in guiding such recognition, and (3) the hypertext system can provide layout facilities that will render later systematic interpretation much easier. Found structures can be used as a basis for supporting information management, as a straightforward way of promoting knowledge-base evolution, as a way of solving representational problems endemic to many hypertext systems, or as a basis for collaboration or interaction.

Aquanet is a collaborative hypertext tool that combines elements of frame-based knowledge representation and graphical presentation. In this paper, we examine the first major application of the tool in an analysis task, a two year long technology assessment that resulted in almost 2000 nodes and more than 20 representational types. First, we cover the implications of the representational resources provided and representational decisions that were made. Then we discuss how spatial layout was used in lieu of the complex relations Aquanet’s data model supports. Finally, we show how distinct regions emerged to reflect particular activities and how they were subsequently used as the basis for a later collaboration on a similar task.

The hypermedia field has long realized the need for firstclass structural abstractions. However, we have failed to generalize the concept of ubiquitous structure management to problem domains other than navigation of information spaces. In this paper, we argue for the recognition of such a generalization, called structural computing, in which we assert the primacy of structure over data. We provide examples of four problem domains that are more naturally modeled with structure than data. We argue that support for structural computing must come in the form of new models, operating systems, and programming languages. We also assert that the experience gained by hypermedia researchers over the last decade may be naturally extended to form the basis of the new field of structural computing, and furthermore, the broadening of the applicability of our work is necessary for the continued vitality of our research community.

This paper presents an approach for providing hypermedia services in this heterogeneous setting. Central notions of the approach include the following: anchors are established with respect to interactive views of objects, rather than the objects themselves; composable, n-ary links can be established between anchors on different views of objects which may be stored in distinct object bases; viewers may be implemented in different programming languages; and, hypermedia services are provided to multiple, concurrently active, viewers. The paper describes the approach, supporting architecture, and lessons learned. Related work in the areas of supporting heterogeneity and hypermedia data modeling is discussed. The system has been employed in a variety of contexts including research, development, and education