[ktpsns]

Well, in principle a CAS like Mathematica (or in principle every mature alternative) allows you to implement such a workflow (i.e. naming mappings or an algebra on your objects). I think what Wolfram is concentrating on since a decade is accumulating "knowledge" into their system, i.e. exactly this kind of semantic information we talk about. However, as an end user I don't really see that, it seems to be more well-groomed behind Wolfram alpha.

On the other hand, there are these research projects which however seem to concentrate on standards rather then actually accumulating semantic knowledge.

I would love to see an adoption of hypertext and semantic mathematical notation in scientific papers. Instead of writing $E=m c^2$ in a (LaTeX) paper, we would instead define the symbols machine readably with a code like

   set E = physics/Energy
   set m = physics/Mass
   set c = physics/constants/speed-of-light

I have never seen actual scientific papers which do this kind of stuff, i.e. which are machine readable.