XML succeeded, and in ways that weren't expected - at least not by many. Originally it was conceived as a document-oriented technology for robust quality publishing of documents over networks. the original workplan had three pillars - XML syntax, XML link, and XML stylesheets. Schemas were not high on the agenda and XML was not seen as an infrastructure for middleware or glueware. It was expected that at some stage it would be necessary to manage data but there was little activity in this area in 1997. When developing Chemical Markup Language (which must be one of the first published XML applications), I found the lack of datatypes very frustrating!
Well, XML is now a basic infrastructure of much modern information. I doubt that anyone now designs a protocol, or operating system without including XML. Although this list sometimes complains that XML isn't as clean as we would like, it works, and it works pretty well.
--Peter Murray-Rust on the xml-dev mailing list, Thursday, February 7, 2002