An Introduction to the XQuery (and XPath 2.0) Type System: The general concepts

One of the most controversial, and in my opinion most often misunderstood aspect of XQuery 1.0/XPath 2.0 is their relationship to types. Many people seem to understand that the type system is based on the W3C XML Schema language (which is true) and then conclude that it is complex (which is only partially true). Also, too many people mix up the notions of weak, strong, static, and dynamic typing. In this and some following posts, I would like to bring some order into the confusion and explain how the type system in XQuery and XPath 2.0 works. First we will introduce a whole bunch of terms and talk about the general concepts. In subsequent posts I will look at the actual XQuery types and some examples and scenarios for weak, strong, static, and dynamic typing.

http://sqljunkies.com/WebLog/mrys/archive/2004/05/13/2480.aspx