A Vision for Open Hypermedia Systems Nürnberg and Leggett

1. Introduction

The Open Hypermedia Systems (OHS) Working Group was formed after the 2nd OHS Workshop, held in conjunction with Hypertext 96. Currently, the OHS Working Group (OHSWG) claims three main areas of interest: scenarios, reference architectures, and protocols. The discussions over scenarios of OHS use are supposed to inform the work on OHS reference architectures, which in turn is supposed to enable the development of an Open Hypermedia Protocol (OHP) that will allow clients of one OHP-compliant OHS to use services of other OHP-compliant OHS's.

Before the scenario, architecture, and protocol work can begin, however, it is important to state the problem being addressed by the OHSWG. Opinions on this subject are necessarily "first principles" that ground further discussion, and as such tend on the one hand to be somewhat arbitrary and on the other hand treated as inviolate axioms from which resultant work must not be allowed to stray too far. There has been neither a consensus nor even a truly concerted effort to derive these principles to date. Like other aspects of the group's work, any problem definition on which the scenarios, protocol proposals, and architecture proposals will rest will ultimately be derived from group discussion on different proposals. We begin this paper by presenting our proposal for a definition of the scope of the group's work.

In the next section, several different scenarios are discussed. Synopses of the points of the scenarios relevant to the paper and links to the full scenarios on the OHS scenarios WWW site are given. Three major implications of these scenarios for the architecture and protocol work are then discussed.

We then provide a proposal for an OHS reference architecture, based on a synthesis of previous proposals (e.g., [Goose et al. 1997] and [Grønbæk and Wiil 1997]), with the modifications suggested by our scenario analysis and OHSWG problem scope definition. We offer this architecture primarily as a way to identify which conceptual entities must communicate with one another to effect hypermedia services for system clients. However, we feel the architecture has generative properties as well, suggesting ways in which future functionality may be added to our initial designs. Brief outlines of how the actual architectures of several OHS's represented in the OHSWG map to our reference architecture are also provided.

We then present our proposal for an OHP, based on the current proposal by Davis et al. [1996], the critique offered by Anderson [1997], the discussion on the OHS mailing list, our reference architecture proposal, scenario analyses, and problem definitions. We feel the protocol itself, or at least its presentation, is somewhat simpler than the current proposal. We intentionally ignore several "hot issues" regarding details of protocol implementation. Where this is done, however, we defend our choice based largely on our reference architecture and discussions on where certain knowledge must reside. Conversely, we elaborate certain aspects of the current protocol work in ways we feel will speed more widespread adoption of the protocol by the OHSWG members.

The primary aim of this paper is to provide the OHSWG with scenarios, architecture and protocol proposals. However, this paper has a secondary aim - an evaluation of the process by which the OHSWG has chosen to perform its work. The first several sections of this paper can be seen as a microcosm of the OHSWG effort, since it contains representatives of all of the elements of the group's product. The last two sections of the paper considers the benefits and drawbacks of this process, evaluates the work of the group against this model, and offers suggestions for future progress.


Peter J. Nürnberg, John J. Leggett
HRL, CSDL, Texas A&M
original page URL: http://jodi.ecs.soton.ac.uk/Articles/v01/i02/Nurnberg/intro.html