A standard property language exists...
It's called "Property Sets"
A property set is an XML document that conforms to the ISO standard DTD for property sets.
Already in commercial use; the software already works with XML.
Every class of information component ("node"), and every property of every class, has a unique name.
These names can be used in queries.
This whole idea is often called "the Grove Paradigm." It's the basis of SGML processing, and the SGML Property Set aided the development of the DOM.