The World Wide Web Consortium's Web Ontology working group has published a working draft of the requirements for its Ontology Web Language (OWL). The working group, part of the W3C's Semantic Web activity, is chartered to create a language that extends the semantic reach of previous metadata efforts based on eXtensible Markup Language (XML) and Resource Description Framework (RDF).

This seemingly abstruse or even incomprehensible undertaking is actually essential if hopes for XML-based communication between enterprises are to be realized. In the current excitement about web services, it is all too often overlooked that there is no point being able to call someone if you cannot then speak their language.

As long as all the parts of a distributed software system are written by a team that shares a single set of data definitions, no fundamental problems arise.

With the advent of web services and service oriented architectures, however, this may no longer be the case. Some web service visions - including the W3C's own Semantic Web - assume that applications will be able to find and invoke services about which their developers knew nothing at all. This can only work if both parties agree on a single set of data definitions: hence the critical importance of shared ontologies.

The OWL requirements working draft identifies key issues such as the use and integration of multiple ontologies across different domains and services; different ontologies for each domain or service; and simple ontology representation. It states that "Ubiquitous Computing" will require "serendipitous interoperability" under unchoreographed" conditions. That is, devices that were not designed to work together should be able to discover each other's functionality and be able to take advantage of it.

It would be foolhardy to doubt the Semantic Web's feasibility - after all, its most famous advocate, W3C director Tim Berners-Lee, was successful with his last major project. But it seems destined to be a long-range project, which will have to crack some tough research problems before it bears fruit.

Shared ontologies are among the more fundamental of these problems, and it is reassuring that the web Ontology working group includes representatives of such organizations as Daimler Chrysler, the Defense Information Systems Agency (DISA), EDS, Fujitsu, HP, Iona, Lucent, MITRE, Nokia, Philips, Stanford University, the University of Southampton, Unisys and W3C itself.

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