Of all the standards to accompany XML that are currently in progress at the W3C, few are more anxiously awaited than the Schema standard - the specification that provides an alternative to XML 1.0 DTDs as a way to describe a document's structure. But what's wrong with XML 1.0 DTDs? How many alternatives have been proposed, and by whom? Why didn't the W3C address these concerns in the original XML 1.0 specification instead of waiting until now? I'll answer those questions in this column, and in my next column we'll look at the current state of the W3C Schema Working Group's unfinished proposal.