The Semantic Web didn't fail because ontologies were wrong
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essay The Semantic Web didn't fail because ontologies were wrong<br>t+t Jeff Reynar · August 7, 2026 · Updated August 16, 2026<br>Ontologies are having a moment again. AI engineers are rediscovering RDF and OWL as a way to keep probabilistic agents inside deterministic boundaries, and reaching for off-the-shelf vocabularies like schema.org and Dublin Core because the models have already seen them. Latent Space covered the revival after UC Berkeley’s Frank Coyle argued at the AI Engineer World’s Fair that probabilistic models need logical guardrails, and Neo4j CEO Emil Eifrem pitched a shared semantic layer that thin agents could run on instead of each one being wired to its own data sources by hand.
I’ve seen three large efforts to make knowledge machine-readable at scale: Smart Tags at Microsoft in 2001, which I helped build; the two SharePoints that shipped the same year, which I watched from across the company; and question answering on google.com in 2005, where I was the PM and later managed the engineering team. Each of them delivered technically but ran into a wall anyway. Maintenance is the reason usually given.
It’s the third of three hard problems. Somebody has to design the schema. Somebody has to populate it before it’s worth anything. And somebody has to keep it current forever. Three problems, solved by people, over and over, and for two decades nothing worth doing it for. None of the three projects were Semantic Web projects, and that’s the point: the formalisms differed but the problems did not. What has changed is that an agent can do the upkeep, and the payoff has arrived, or at least enough people believe it has that RDF and OWL are back on the table. I want to say up front that I’m building a company in this space.
I believed in all three projects at the time. What makes this revival different is not that I believe harder, but that keeping a model current can now happen as a byproduct of the work instead of being somebody’s job.
The short version<br>The Semantic Web is usually said to have failed for being too academic. SQL is the counterexample. It’s harder and stranger, and it won completely. The problem was difficulty relative to value, and the Semantic Web was hard in three separate places rather than one. Someone has to design the schema, which is not engineering work and was nobody’s job. Smart Tags shipped an SDK for it but the types never came, and the SharePoint that assumed a taxonomist lost to the one that assumed nobody. Someone has to populate it. Question answering on google.com read the web without anyone entering a fact, but each new domain waited on an engineer to write its extractor. Then someone has to keep it current forever, and nine years on, Microsoft’s answer to that was still a job title you had to hire for. Three hard problems, and for twenty years no benefit big enough to justify solving them. What’s different now is that an agent can do the upkeep as a byproduct of its own work, and structured knowledge finally has clear value, because agents need it.
Three attempts
Before joining Microsoft in 1998 to work on semantic annotation, I did a PhD in natural language processing. We productized research from labs and universities and shipped Smart Tags in Office XP in 2001.
As an aside: the better-known Smart Tags story is the browser one. Microsoft pulled that feature from Internet Explorer 6 in June 2001 after publishers objected to Microsoft turning their words into links of its choosing. That fight was about who controls a web page. The Office version shipped, and faded for another reason.
Every smart tag had two components: a recognizer and an action. The recognizer decided that a string was of a certain type. The action offered you verbs for it. Email this person, add this date to your calendar, look up this stock. We shipped those and let you build your own as well.
Microsoft shipped an SDK so that companies could define the types that mattered in their own business and attach the actions worth taking against them. That’s where it broke down, before maintenance was ever the issue. Developers turned out not to be good at identifying those types, or at inventing the verbs to go with them. Neither is the work of a software engineer. And it wasn’t really anyone’s job.
If nobody owns the work, there are two ways out: make it someone’s job, or build something that doesn’t depend on the work. Microsoft tried both at once, and I had a front-row seat. In 2001 it shipped two SharePoints. Portal Server, released to manufacturing that March, was the serious one. It organized documents by category, with category folders, document profiles and property definitions as first-class objects. It was built for the companies best equipped to do that properly, large enough to have a person, or a whole team, whose actual job was owning the taxonomy. Team Services was the other one, broadly...