This is pretty much the crux of the problem that the Semantic Web / Linked Data folks have been working on for years. They have the technology to do it (RDF). T

This is pretty much the crux of the problem that the Semantic Web / Linked Data folks have been working on for years. They have the technology to do it (RDF). This technology is not widely used for a number of reasons, but "because it can never exist (and I'll write that in boldface for extra credibility)" is not one of them. People have been able to agree on many common vocabularies of stuff, like "<h1>" and "<svg:ellipse>" and "rel=pingback", and have it work more or less. It is not absurd to suggest that such an agreement can be achieved -- to some extent -- in APIs.