Simple knowledge text format

I need to start coming to grips with the need to be able to represent "knowledge" in some easy to use text format, presumably XML.  This includes ontologies, taxonomies, reference data, entity attributes, entity relationships, etc.

A full-blown XML format would probably be far too cumbersome for everyday usage.  Rather, I'd like to come up with a generic simple text format as well as "mini parsers" (and formatters) that would let the user use variable syntax that can be adapted to specific knowledge domains.  The knowledge file could then be trivially toggled between the simple text format and the full XML format, at will, as needed.

Somebody may have or prefer a GUI editor, but editing the simple-text format should be a credible option as well.

Anybody have any advice and experience?

-- Jack Krupansky