Are there any established ways of representing mathematical formulas or expressions in RDF?
A web search turned up a paper by Marchiori (2003) which provides an overview of relevant Semantic Web standards, and even contains an example of how a MathML fragment like this:
<apply> <csymbol encoding="text" definitionURL="http://www.mathsw.org/scalarplus"> p </csymbol> <cn> 2 </cn> <cn> 6 </cn> </apply>
could be represented in RDF like this:
:_1 <http://www.w3.org/TR/MathML2#apply> :_2 :_1 <http://www.w3.org/TR/MathML2#csymbol> "p" :_1 <http://www.w3.org/TR/MathML2#definitionURL> <http://www.mathsw.org/scalarplus> :_1 <http://www.w3.org/TR/MathML2#encoding> "text" :_2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#:_1> "2" :_2 <http://www.w3.org/1999/02/22-rdf-syntax-ns#:_2> "6"
However, that was just an example, and I couldn't find anything which would describe a complete framework for something like that.
Edit for clarification. I am looking for something which would allow to represent mathematical expressions which refer to other resources described in RDF as sub-expressions. Even perhaps something that would allow to construct mathematical expressions by some sort of rule language (like SPARQL CONSTRUCT queries). Therefore just using MathML (or OpenMath) markup in a XML Literal does not seem like a good solution.