Chapter 5. Introduction to the Formal Semantics

Mary Fern ndez, J r me Sim on, and Philip Wadler

"When a Mathematical Reasoning can be had it's as great a folly to make use of any other, as to grope for a thing in the dark, when you have a Candle standing by you."

” John Arbuthnot, The Laws of Form, 1692

XQuery is described by two documents: the XQuery language document [XQ-LANG], which uses prose, and the XQuery Formal Semantics document [XQ-FS], which uses symbols. Symbols support a degree of precision that prose alone cannot achieve, but they require some training in their use. This chapter provides such training and is intended for XQuery implementers and expert users who need a deeper understanding of XQuery's semantics.

This chapter does not describe the XQuery Formal Semantics in its entirety. Our aim is to teach enough about the notations and techniques used in that document so that you can go off and read it yourself. A basic understanding of XQuery is a prerequisite to this chapter. We suggest reading Chapters 1 and 4 before studying this chapter.

As of this writing, XQuery and its formal specification are still in working draft. The material presented in this chapter is expected to be aligned with the May 2003 working drafts.