1.8.      Hypermedia in the Hermes System

In Greek mythology, Hermes supported human interpretation by providing the gift of spoken and written language and by delivering the messages of the gods. As part of the research for this dissertation, a prototype software system named Hermes has been designed to support the preconditions of interpretation (a) by represent­ing the design construction situation to support prepossession, (b) by provid­ing alternative perspec­tives to support preview, and (c) by including a language to support preconception.

Hermes supports tacit knowing by encapsu­lat­ing mechanisms corresponding to each of the preconditions:

*    Interpretive critics (Fischer, et al., 1993b) are used for analyzing the design situation, which is represented in arbitrarily complex hypermedia data structures. These critics are expressions in the Hermes language that perform an analysis of the current state of some representations and then optionally display a message. The evaluation of the critic expressions or rules is dependent upon the currently active interpretive perspective, which determines the versions of the expression, of its constituent terms, and of the representations being analyzed.

*    Named perspectives (Stahl, 1993b) organize and manage alternative sets of information relevant to different purposes. By switching to a new perspective by selecting its name from a list, a designer can change how the representation of the situation appears, what interpretive critics are active, and in general what contents of the hypermedia network are “visible” from the viewpoint.

*    Language terms (Stahl, et al., 1992) define computations across the knowledge base. While these expressions can be arbitrarily complex if viewed in complete detail, they are typically constructed in a series of stages. At every stage, the components of the term’s definition can themselves be given names.

With each of these mechanisms, complexities are hidden from the user by being encapsulated in named objects. These complexities can gradually be made explicit upon demand so the designer can reflect upon the information and modify it. Together, these and other mechanisms make Hermes a computationally active medium in which designers can do their work.

Hermes is a knowledge-representation substrate for building computer-based design assistants like the Lunar Habitat Design Environment (Lhde) shown in Figure 1-3. It provides a hypermedia structure for designers to build representations of design knowledge.

Figure 1-3. Arranging sleep compartment bunks using Hermes.

Windows shown (left to right) include a dialogue box for browsing the hypermedia content, a selection from the design rationale issue-base, a critic rule’s message, a graphical sketching area, and a button for changing interpretive perspectives.

The network of knowledge corresponds to the design situation. Multi-media nodes of the knowledge representation can, for instance, be textual statements for the issue-base, CAD graphics for sketches, bitmap images to illustrate ideas, or language expressions for critics and queries. The inter-linked hypermedia structure facilitates browsing by designers. It can also be used to support associative memory (Hinton & Anderson, 1989) or case-based dynamic memory (Schank, 1982; Kolodner, 1984). All displays are defined by queries that dynamically assemble arbitrary collections of multimedia items. For instance, the Design Rationale window in Figure 1-3 shows the textual issues, answers, and arguments that resulted from a query that was executed by a user’s request to see the “discussion” of a previously viewed issue.

The hypermedia knowledge representation structure of Hermes is designed to facilitate the representation of design situations and to encourage their tailorability. Its generalized node and link structure models the network character of the situation as a network of inter-related, pre-understood significances and their associations. Its object-oriented implementation allows for the integration of information in different media—reflecting the need to bring together many forms of information in design. It provides graphics for sketching, text for issue-bases or design rationale, and other media for annotations to support the exploration of represented situations. All the media and mechanisms are designed to maximize plasticity of representation. The Hermes hypermedia structure incorporates a perspectives mechanism for managing and viewing all information and an end-user language for defining queries for displays, as discussed below.

Special emphasis is placed on the synergistic integration of the hypermedia, perspectives, and language mechanisms in the Hermes substrate. Definitions of perspective hierarchies and language expressions are stored in the hypermedia network so they can be browsed and modified like all other information. By using nodes of the hypermedia network to define the names of perspectives and links to determine the inheritance relationships among perspectives, the Hermes system can support annotation of these nodes to store information related to the purpose or origination of the perspectives. Similarly, the nodes that define terminology and expressions in the Hermes language can be linked like a semantic network (Quillian, 1967).

In turn, the definition of the hypermedia structure itself incorporates both perspectives and language expressions. Instead of having a fixed content in some medium, nodes can have their content defined by the evaluation of an expression in the language. Nodes and links can be conditional upon some computation defined in the language and involving other nodes and links. Furthermore, hypermedia information to be displayed is always dynamically computed in the currently active perspective—even language expressions can have different effects in different perspectives. In these ways, node contents can be dependent upon the state of other data in the hypermedia network. The interactions of the integrated hypermedia, perspectives, and language provide significant control and malleability for the designer. Design environments built on this substrate can have many features that support interpretation in design with consistent abilities to represent knowledge and to tailor the representations.

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This page last modified on January 05, 2004