Hypertext On Generalizing the Introduction The core idea of hypertext has been described Concept of Hypertext cieariy and accurateiy: The concept of hypertext is quite simple: By: Michael P. Bieber Windows on the screen are associated with Computer Science Department objects in a database, and iinks are pro- Boston College vided between these objects, both graphl- caiiy (as iabeiied tokens) and in the Chestnut Hill, Massachusetts database (as pointers) (Conklin. 1987, p. 02167-3808 U.S.A. 17) Steven 0. Kimbrough (See aiso Nieisen, 1990, and Shneiderman and Decision Sciences Department Kearsiey, 1989, for book-length introductions to The Wharton School hypertext.) University of Pennsylvania Stiii, as is universatiy recognized, there is more Phiiadeiphia, Pennsylvania to the idea of hypertext than iinked information 19104-6366 U.S.A. items that allow a user to explore ideas and pur- sue thoughts in a free and "non-iinear" fashion. After ail, weli-designed standard computer ap- Abstract plication programs, including reporting systems and decision support systems, have long Hypertext has quickly become an established delivered such capability, at ieast to a respectable paradigm in the design of information systems. degree. What hypertext systems add, with their The success of products in the software market, emphasis on the vaiue of iinked information evident benefits as reported by users, and the items, is: (1) easier, richer, more highiy featured flowering of related research activity all attest to iinking of information; and (2) system-level, rather the significance and staying power of hypertext- than application-ievel, support for creating, main- rich information systems. Although standard taining, expioiting, and managing iinked informa- hypertext has a number of unquestioned benefits, tion items (Bieber, 1991). Like database systems, the concept also has a number of well-known pro- report generators, graphics packages, and user blems and limitations. This article reviews the interface management systems, hypertext soft- main problems and limitations of basic (standard) ware can be seen as application-independent, hypertext that constrain the use of hypertext in system-ievei toois for providing usefui features practical applications. Further, this article for specific appiications. presents and discusses our "generalization" of the basic hypertext concept, which we call Our aim is to describe and discuss certain ex- generaiized hypertext. These generalizations en- tensions at the system level to the core ideas of compass, among other things, automatic crea- hypertext, which we call generalized hypertext. tion of hypertext elements. Generalized hypertext We have been motivated to deveiop generaiized promises to be more powerful than standard hypertext concepts as part of a iarger effort, fund- hypertext as well as less expensive to implement ed by the U.S. Coast Guard, to develop decision and maintain. To illustrate these concepts, we support system shelis, i.e., system software for describe the implementation of a decision sup- generating particuiar decision support systems port system currently in use by the U.S. Coast (Bhargava, et ai., 1988; Kimbrough, 1986; Kim- Guard. brough, etal.. 1990a; 1990b; Minch. 1990). Our purpose in this articie is mainiy to describe these Keywords; Hypertext, generalized hypertext, concepts, the reasons for them, and their present hypertext computation, virluai iinklng. impiementation. dynamic iinking, decision support systems, information presentation The paper is organized as foiiows. In the next section, we present briefiy the core concepts and ACM Categories: H.1.0, H.3.4, H.4.2 vocabulary for basic hypertext, as well as certain MIS Quarterly/March 1992 77 Hypertext problems and limitations of this hypertext con- represents a particuiar iink in the hyperdocument, cept. These problems and iimitations are wideiy e.g., XX. which links nodes AA and BB. recognized. They are the primary motivation behind our concept of generaiized hypertext, Typicaiiy, a user sees a node dispiayed in a win- which is the main focus of this articie. We then dow, its buttons highiighted in some fashion. The present the essentiai ideas of generaiized user expiores the hyperdocument by, e.g., click- hypertext, foiiowed by a discussion of our im- ing on a particuiar button, thereby causing the plementation of the system. system to find the internal representation of the link named by the button, to then traverse the link, to find the node at the link's endpoint, and to display that node as another text passage. The Basic Hypertext newly displayed node may have buttons as well, which the user may employ in order to continue Our aim in this section is to briefly present and exploring the hyperdocument. Alternatively, the discuss basic hypertext. In the foiiowing section user may at any time decide to return to an eariier we shaii contrast this with the generalized node and explore from there. Users may continue hypertext system that we have conceived, in this way more or less indefiniteiy, thereby ex- developed, and implemented. Certainly, many pioring at wiii the hypertext network. A particuiar existing systems have richer feature sets than we hyperdocument—a coiiection of nodes and iinks shaii describe in connection with basic hypertext, —may be thought of as an application written but our focus in this atlicie is on generaiizations under the hypertext system, it is the system that to the basic hypertext concept. Further, aithough provides the general means for exploring the par- we shaii iimit our discussion to hypertext, most ticular hyperdocument. Thus, a basic hypertext of what we say (when not describing our im- system may be thought of as operating a select- piementation) can be applied as weii to traverse-display loop. The user selects a button, hypermedia.' the system traverses the iink named by the but- The central concept in hypertext is that of iinked ton, and the system dispiays the node at the far coiiections of information. A hypertext document end of the iink. possibiy using information picked may be seen as a graph, with nodes that are coi- up in traversing the iink. iections of information (caiied, e.g., windows (Conkiin, 1987), documents (Brown, 1987; 1989; Typicai, basic operations supported by hypertext Haan, et ai., 1992), cards (Appie Computer, 1989; systems inciude: Halasz, 1988), information items (Bhargava, et al., 1988), chunks (or pieces of text) (Koved, • User-directed navigation (traversai (of iinks) 1988; Trigg, 1983), frames (Akscyn, et al., 1988)). and dispiay (of nodes)) of the hyperdocument. Links specify reiationships between nodes. They • Search and dispiay (for example, the user will may have properties themseives and faii into provide a search string and the system wili types. They are maintained by the system, and search until it finds a node containing that are named or referred to by buttons (aiso caiied string and then wili display the node). link icons (Conklin, 1987) and link markers (iHaiasz and Schwartz 1990)), which normaily are • Map-based navigation (the system dispiays a found in the nodes. To iliustrate, see Figure 1 graph (called a map or network overview) of (based on Conkiin, 1987), where nodes Window the hyperdocument, and the user may direct A and Window B are presented as windows on navigation of the hyperdocument based on the the dispiay. Within the nodes are the buttons x, map, whose buttons, when selected, cause the y, z. What is displayed represents part of the corresponding node in the hyperdocument to underiying hyperdocument (network of hypertext be dispiayed). nodes and links). Window A is a representation of node AA in the hyperdocument, and Window • Creation, modification (e.g., editing the con- B represents BB. Simiiarly, a button, e.g., x. tents of a node), and deietion of nodes and iinks and their attributes. • Display of iink and node attribute information ' The hypermedia concept extends hypertext to types of infor- (e.g., the name of the node at a iink's endpoint, mation items besides text, such as graphics and sound (Haan, et ai., 1991). the type of node or iink). 78 MIS Quarterly/March 1992 Hypertext Underiying Hyperdocument: Hypertext Database BB CC AA yy Figure 1. Central Hypertext Concept • Procedural attachment (link endpoints may be explain and discuss the keyword in question. procedures that are activated by traversal of The hypertext system might infer a link (and their incoming iinks. These procedures typical- thus the existence of an accompanying but- ly affect how certain nodes are displayed (see ton) by being abie to recognize keywords in ar- Apple Computer, 1989; Halasz, 1988; Koved, bitrary nodes and dynamicaiiy creating buttons 1988, and Thompson, 1990). out of them that are iinked to the appropriate keyword nodes. With such a capability, a However interesting this basic hypertext concept builder couid simpiy type text into a node and is, and however usefui various implementations have the system create many of the needed of it have proved to be, a number of probiems buttons and links associated with that node.^ and limitations have been identified with this Clearly, there is considerable potentiai basic concept (Bhargava, et ai., 1988; Conkiin, benefit—especiaiiy in terms of reducing the 1987; Feinerand McKeown, 1991; Halasz, 1988; cost of buiiding a hyperdocument—to having Van Dam, 1988). For this article we are the hypertext system capable of creating but- concerned with the foiiowing widely recognized tons and iinks automaticaiiy. probiems and limitations in basic hypertext (and in many current impiementations of hypertext). Manual node creation (Bhargava, et al., 1988; Halasz, 1988; Jordan, et al., 1989; Parunak, • Manual iinking (Bhargava, et ai., 1988; 1988). This is the node version of the above DeRose, 1989; Feiner and fwIcKeown, 1991; link limitation. Under the basic hypertext con- Haiasz, 1988; Jordan, et ai., 1989; Van Dam, cept, the hyperdocument builder builds nodes 1988). Basic hypertext systems provide editing by using an editor to key in or to paste in in- features for linking existing nodes and for formation.