Organization and Roadmap

Your approach to this material will depend on your specific experience and interests. Here's a quick roadmap to the four parts of the book and a look at the individual chapters to help you figure out where to dive in first.

  • Part I: Basics

  • Part II: Background

  • Part III: Formal Underpinnings

  • Part IV: Databases

Part I: Basics

Jonathan Robie's "XQuery: A Guided Tour" provides a good starting point if you're new or relatively new to XQuery. Its easy, tutorial-like style invites you to read it straight through. Jonathan provides a compact and convenient reference to XQuery's key features that newcomers and experts alike can return to periodically for a quick refresher on the basics while working through the detail in the other chapters. Jonathan's coverage is extensive ; most of the entries in the glossary (a useful resource when you're stumbling across new terminology) are introduced in this chapter. (Note that glossary entries are bolded the first time they appear within the text.)

Part II: Background

The two chapters in Part II provide historical context and a detailed rationale for many of the complex technical decisions the Query working group has had to make as the language has evolved.

As Don Chamberlin explains in Chapter 2, "Influences on the Design of XQuery," the process of designing XQuery has been one of resolving the tensions between conflicting goals, and his chapter provides a historical and technical description of that dialectic in action. This chapter also places XQuery in the context of the other related languages and standards with which it coexists. The second half of the chapter deals in cogent detail with the intricacies of what Don calls " watershed issues": eight complex and often controversial issues that have had a major impact on the design of the language. Don goes a long way to teasing apart the complexities.

As Michael Kay notes in Chapter 3, "XQuery, XPath, and XSLT," the fact that both these languages share a common data model, as well as a common sublanguage in XPath, is a major achievement of the W3C. His chapter explores that commonality and the overlap in functionality between the two languages, as well as their differences. This chapter describes where each language might be employed to best advantage. Mike addresses some of the same issues discussed by Don Chamberlin in the previous chapter but from the particular perspectives of XPath and XSLT.

Part III: Formal Underpinnings

Both chapters in Part III were written by Mary Fern ndez, J r me Sim on, and Philip Wadler. Chapter 4, "Static Typing in XQuery," is a gentle tutorial that explores the ramifications of static typing in a language dealing with XML data. Despite the term formal in the title of this part, this chapter fits naturally here because it provides such a great lead-in to the chapter on the formal semantics ”the topic isn't difficult or particularly heavy. Static typing is important to XQuery developers because it helps to guarantee program correctness, and it helps significantly to speed up the development cycle, as this chapter attests. Users need to understand the concept of static typing in order to better understand the error messages returned by the query system they're working with.

Chapter 5, "Introduction to the Formal Semantics," is a tutorial-like introduction to the formal semantics, the formal mathematical system on which XQuery is built. This is the most challenging technical component of XQuery. This chapter should appeal to implementers, language theoreticians, and those just terminally curious about this aspect of the language. They will find here a much less daunting approach to the formal semantics than that provided by the specification.

Part IV: Databases

Most major relational database vendors already have or will shortly provide support for XQuery as a front end for relational data, and interest in XQuery from this market sector was one of the driving forces behind its development. Chapters 6 and 7 deal with the topic of XQuery and relational data. The authors collaborated on the content so that the chapters would fit seamlessly together. The last chapter in this part describes the features of what its author refers to as an XML database management system.

XQuery was designed to query XML, and using it to query and pull data out of relational databases that store information in tabular format poses a number of interesting challenges. Denise Draper explores these issues in "Mapping between XML and Relational Data."

Michael Rys's chapter, "Integrating XQuery and Relational Database Systems," builds on the foundation laid in Chapter 6. Michael shows two methods of accessing XML stored in a relational database. One approach uses the XML datatype to store XML into the database as an LOB (large object) and accesses that data using a combination of both XQuery and SQL. He also describes a so-called "top-level XQuery" approach that obviates the need to use SQL altogether.

Jim Tivy's concluding chapter, "A Native XML DBMS," rounds out the offerings in this part. Jim describes the key features of what he calls an XML database management system and explores what that means. He looks at the use of the XQuery data model in that context and explores other XML DBMS features such as command languages and APIs, drawing on his experience with XStreamDB (his own native XML database product), Tamino, and the XML:DB Initiative.



XQuery from the Experts(c) A Guide to the W3C XML Query Language
Beginning ASP.NET Databases Using VB.NET
ISBN: N/A
EAN: 2147483647
Year: 2005
Pages: 102

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