Too many development books are slanted towards either concepts or practical, in-the-trenches development. This book manages to balance both by giving not only the what's and why's, but the how to's, and does so in a readable and highly credible manner.The discussion about why Xquery instead of Xpath, XSLT or even direct access through another programming language shows both the strengths and some weaknesses of Xquery. This discussion extended into documents, databases, the state of the Xquery specification, and culminated in a essential types, and types you will not need. This is both conceptual and practical.For the developer who wants to get up-to-speed with (or refine skills in) Xquery, this book goes deep into every facet, using concepts, concrete examples, and code. More importantly, the author's extensive experience is shown in Chapter 11, which covers problem areas and common points of confusion. This short chapter will prove invaluable to new developers. I also liked the chapter on query optimization, and the rich reference material in the appendices, which is almost half of this book.If you want to learn Xquery, hone existing skills, or step back and see the big picture this book is the best one in my opinion. Expect in-depth technical information, and expect it to be provided by someone who understands developers and provides the code to make it real.