W3C Web Services Workshop Position Paper

Protocol for Accessing RDF-based Registries

James Tauber, Bowstreet

The information stored in a registry can typically be modeled as a collection of resources with properties. This is true regardless of whether the underlying implementation of the registry is a relational database, directory service or otherwise.

The Resource Description Framework (RDF) provides:

RDF, therefore, provides a means of representing registry information as well as defining schemata for specific registries.

What is needed is a protocol for accessing such a registry—a means by which RDF-based information may be queried and modified. Too often, a registry protocol is specific to the schema of the registry. I would like to suggest an architecturally cleaner approach where a generic protocol is define that enables querying and modification of any RDF-based information, regardless of schema.

The definition of an application-specific registry then becomes simply a matter of defining an RDF schema for the information to be contained in the registry. The registry access protocol would be generic and not tied to the particular application.

The data model of RDF is very similar to that of a directory information base in X.500 or LDAP. For this reason, it may be possible to leverage LDAP in the design of the generic RDF-access protocol. The Directory Services Markup Language (DSML), version 2 of which is being developed under OASIS, is defining a series of XML messages for querying and modifying LDAP directories. This work would potentially be a valuable input to the RDF-based registry access protocol work being proposed in this paper.

It is envisaged that the protocol would be a lightweight set of W3C XML Protocol messages.

Note that separate to this proposal, but related, is the notion that web service descriptions should be in RDF.