Open Hypermedia Systems Working Group
Framework area compendium
1997.10.30
Open Hypermedia Systems Working Group
Framework area compendium
1997.10.30
4.0 Framework
Kenneth M. Anderson, U California-Irvine, USA
4.1 Component framework
Kenneth M. Anderson, U California-Irvine, USA
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The Open Hypermedia Protocol (OHP) 1.2 and 2.0 specifications contain the definition of an on-the-wire message format to be used for passing messages between hypermedia clients and open hypermedia systems. Each message contains a message header (message id, version id, session id, and user id) and then message-specific data. A critique of the 1.2 OHP specification identified several issues concerning the message format which needed addressing. Some of these issues were addressed in the 2.0 OHP specification, however at the 3.5 Open Hypermedia Working Group Meeting a concern was raised that the definition of a message format is too low-level to be productively handled by this group.
As an alternative, it was suggested that the working group specify the functionality of the OHP via an application program interface (API) to a set of objects and then use one of a variety of existing software component frameworks to produce an implementation of the protocol. Since these frameworks provide support for passing messages between remote objects (actually the mechanism makes the location of an object completely transparent to the caller), the on-the-wire issues surrounding the OHP message format would be handled automatically by the framework.
It was agreed to begin specifying OHP services in the terms of an API and to form the OHS-Framework subgroup to evaluate the existing component technologies and make a recommendation as to which technology to use. In the meantime, CORBA's interface definition language (IDL) is being used to specify the methods and datatypes of the API. This choice does not imply that CORBA's component framework will be the technology used to implement the OHP, however.
Since component technologies are often associated with a non-trivial infrastructure, a concern was raised that the entry barrier to using the OHP was being raised too high for the casual developer. It was suggested that work on the existing message format as specified in the 2.0 OHP specification continue so that low-entry barrier implementations of the OHP might be produced independent of a component framework. The OHS-Framework subgroup was tasked with determining the feasibility of providing a parallel implementation of the OHP that makes use of a pre-defined message format. It is assumed that the existing 2.0 OHP message format would be used (after it has been modified to fully respond to the issues raised by the 1.2 OHP critique). The primary design problem facing this alternative implementation is maintaining compatibility with the component-based version of the OHP.
There are three candidate component technologies which will be evaluated by the OHS-Framework subgroup:
These frameworks will be evaluated in terms of their provided functionality, ease-of-use, cross-platform support, and the availability of the technology.
The products of this subgroup include:
The last item in this list will only be delivered if the OHS-Framework subgroup concludes that this alternative implementation approach is a worthwhile pursuit.
4.2 Naming
Kaj Grønbæk, U Aarhus, Denmark
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Open Hypermedia Systems Working Group