A Vision for Open Hypermedia Systems Nürnberg and Leggett

3.2.2 External Entities
Whatever the form the OHS reference architecture takes, it will be the case that there will be entities outside of the architecture. Several kinds of such "outside" programs are illustrated in the external scenario summarized in Section 3.1. What are the implications for this in our architecture work?

Essentially, we must not try to model things that occur outside the OHS in our architecture. It is our contention that this is exactly what is done in the current proposals by Grønbæk and Wiil [1997] and Goose et al. [1997] when entities such as document management systems (DMS's) are included. To take the DMS's as an example, consider that there are two ways in which these systems are considered in the current proposals: either clients or servers may interact with DMS's.

If clients do so, this is clearly not our concern, since clients may perform open, arbitrary computation. This is not relevant to our task, which is to specify the client's interactions (or their form) with the OHSWG servers.

Servers may interact with DMS's in two ways. A DMS may be a client, in which case there is no reason to explicitly name the type of client or differentiate it in any way from other clients. It may also be a "store" acting as a place in which the server stores hypermedia or other data. In this case, again, it must be asked why this is differentiated from any other store. Either it is "wrapped" per the HyperDisco [Wiil and Leggett 1996] method, and thus looks like any other store, or it is not, in which case this interaction is too specific to be considered in the reference architecture.

Of course, a single instance of a DMS could act as both client and store to a server, or as a store for both clients and servers. Is this problematic? Perhaps, but again, this is true for a broad class of stores. There seems to be, in general, no support for treating DMS's separately from other kinds of programs, whether they be clients, stores, or combinations.

Our architecture proposal is based on the premise that there is no particular reason to enumerate or differentiate entities external to the issue at hand of defining a reference architecture for OHS's. They should be excluded from consideration or generalized to a broader, more applicable class of entity.


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