UISIC XML Group:
International Union of Speleology, Informatics Commission XML Working Group
W3C XML: good starting point for Schema (see below), XLink, XPointer and available software.
W3C XML Schemas Page: very good list of tools, tutorials, and the XML Schema specifications.
Cave Survey Software
Survex Cave Surveying Software: An comprehensive set of cave survey software developed by Olly Betts and others. Works on many platforms (Linux, Windows and DOS), data format is ASCII and programs are open source.