My recent discussions with the ODP guys about open-sourcing the ODP backend software have led me to read up on RDF, which is the format used by ODP for exporting the ontological information and content of the directory. One thing I immediately ran into was XTM, the ISO standard for creating XML Topic Maps. These seem to me to be competing standards in that they both use XML to describe ontological information. RDF seems to be enjoying much more widespread use on the web but I’m playing catch-up in this particular area right now, so I may be missing some uses of XTM. One helpful document I’ve found is a paper by Lars Marius Garshol comparing XTM, RDF, and two RDF extensions, DAML and OIL. If anyone knows of other introductory-level documents describing the similarities and differences of XTM and RDF, I’d be curious to hear about them.