Ubiquitous semantic interoperability is like world peace: It's a goal so grandiose, nebulous and contrary to the fractious realities of distributed networking that it hardly seems worth waiting for.

In most circumstances we can assume that heterogeneous applications will employ different schemas to define semantically equivalent entities -- such as customer data records -- and that some sweat equity will be needed to define cross-domain data mappings for full interoperability.

Nevertheless, many smart people feel that automated, end-to-end, standards-based semantic interoperability (where computers exchange not just data but the data's meaning as well) is more than a pipe dream. Most notably, the long-running Semantic Web initiative of the World Wide Web Consortium (W3C) just keeps chugging away, developing specifications that have fleshed out Tim Berners-Lee's vision to a modest degree and gained a smidgen of real-world adoption.

If nothing else, the W3C can point to the Resource Description Framework (RDF) -- the first and most fundamental output from this W3C activity -- as a solid accomplishment. Created just before the turn of the millennium, RDF -- plus the closely related Web Ontology Language (OWL) -- provides an XML- and Uniform Resource Identifier (URI)-based grammar for representing diverse entities and their multifaceted relationships.

RDF, OWL and kindred W3C specifications have not exactly taken the service-oriented-architecture (SOA) world by storm, however. In fact, you'd be hard-pressed to name a single pure-play vendor of Semantic Web technology that's well known to the average enterprise IT professional.

Also rare is the enterprise IT organization that's looking for people with backgrounds in or familiarity with Semantic Web technologies. This remains an immature, highly specialized niche in which academic research projects far outnumber commercial products and in which most products are point solutions rather than integrated features of enterprise databases, development tools and application platforms.

Part of the problem is that from the start, the focus of W3C's Semantic Web initiative has been more Utopian than practical. If you tune into Berners-Lee's vision, it seems to refer to some sort of super-magical metadata, description and policy layer that will deliver universal interoperability by making every networked resource automatically and perpetually self-describing on every conceivable level. Alternately, it seems to call for some sort of XML-based tagging vocabulary that everybody will apply to every scrap of online content, thereby facilitating more powerful metadata discovery, indexing and search. The success of the whole Semantic Web project seems to be predicated on the belief that these nouveaux standards will be adopted universally in the very near future.

Needless to say, this future has been slow to arrive. Commercial progress on the Semantic Web front has been glacial at best, with no clear tipping point in sight. It's been eight years since RDF was ratified by W3C, and more than three years since OWL spread its wings, but neither has achieved breakaway vendor or user adoption.

To be fair, there has been a steady rise in the number of semantics projects and start-ups, as evidenced by growing participation in the annual Semantic Technology Conference, which was held recently in San Jose, Calif. And recently there has been a resurgence in industry attention to semantics issues, such as the recent announcement of a Semantic SOA Consortium. Some have even attempted -- lamely -- to rebrand the Semantic Web as "Web 3.0," so as to create the impression this is a new initiative, not an old effort straining to stay relevant.

The SOA market sectors that one would expect to embrace the Semantic Web have largely kept their distance, however. In theory, vendors of search, enterprise content management, enterprise information integration, enterprise service bus, business intelligence, relational databases, master data management and data quality all would benefit from the ability to harmonize divergent ontologies automatically across heterogeneous environments.

Only a handful of vendors from these niches -- most notably, Oracle, Software AG and Composite Software -- have taken a visible role in the Semantic Web community, however -- and even these vendors seem to be taking a wait-and-see attitude. One big reason for reluctance is that there already are many established tools and approaches for semantic interoperability in the SOA world, and the new W3C-developed approaches haven't yet demonstrated any significant advantages in development productivity, flexibility or cost.

One of the leading indicators of any technology's commercial adoption is the extent to which Microsoft is on board. By that criterion, the Semantic Web has a long way to go, and may not get to first base until early in the next decade, at the very least. The vendor's ambitious road map for its SQL Server product includes no mention of the Semantic Web, ontologies, RDF or anything else to that effect.

So far the only mention of semantic interoperability in Microsoft's strategy is in a new development project code-named Astoria. Project Astoria, which was announced in May at Microsoft's MIX conference, will support greater SOA-based semantic interoperability on the ADO.Net framework through a new Entity Data Model schema that implements RDF, XML, and URIs. Microsoft has not committed to integrating Astoria with SQL Server, however, nor is it planning to implement any of the W3C's other Semantic Web specifications. Essentially, Astoria is Microsoft's trial balloon to see if a Semantic-Web-lite architecture lights any fires in the development community.

Clearly there is persistent attention to semantic interoperability issues throughout the distributed computing industry, and Microsoft certainly is not the only SOA vendor at least pondering these issues on a high architectural plane. The W3C's Semantic Web initiative indeed could be the seedbed of a new, semantics-enabling SOA, although it could take a lot longer for this dream to be realized fully. It might take another generation or so before we see anything resembling a universal semantic backplane that spans all SOA platforms.

After all, the Utopian hypertext visions articulated by Vannevar Bush in the 1940s and Ted Nelson in the 1960s had to wait till the 1990s, until Tim Berners-Lee nudged something called the World Wide Web into existence.