XML Processing

Web service applications often pass information using XML documents. Application developers whose applications accept XML documents must understand how best to extract information from these XML documents and use that information in their business processing. They must also understand how to assemble XML documents from the results of this business processing.

This chapter provides an extensive coverage of XML document handling. To make it more manageable, you may want to concentrate on the sections of particular interest to you. These sections are as follows:

• XML Overview--Provides an overview of basic XML concepts. If you are not familiar with XML, this section provides a concise summary of key XML concepts and technologies. Even if you do know XML well, you may want to skim this part since it highlights issues important for designing XML-based applications.
• Outline for Handling XML Documents--Describes how applications typically handle XML documents.
• Designing XML-Based Applications--Covers such design topics as receiving and sending XML documents, validating XML documents, mapping XML documents to data objects, applying business logic on documents or objects, and keeping business processing logic separate from XML processing logic. This discussion also includes recommendations that help determine how to best design an XML-based application. Architects and application designers should find this section of particular interest.
• Implementing XML-Based Applications--Provides guidelines for developers on how best to implement XML-based applications. This section includes an in-depth discussion of the various XML-processing technologies that developers can use to implement their applications. It covers the advantages and disadvantages of the principal XML programming models and provides recommendations for when you should consider using each of the models.
• Performance Considerations--Outlines guidelines for maximizing performance. This section makes specific recommendations for approaches developers can take to keep performance at an acceptable level.

Many of these concepts for designing XML-based applications are generic in nature; they apply to any application handling XML documents. Since Web services are XML-based applications, these concepts especially apply to the design of Web service endpoints and clients. The chapter emphasizes the design considerations that should be kept in mind when developing Web service endpoints and clients.

Although it presents the basic XML concepts, this chapter assumes that you have a working knowledge of the XML processing technologies, especially SAX, DOM, XSLT, and JAXB. (Refer to Chapter 2 for more details on these technologies.) Whenever possible, the chapter uses the scenarios introduced in Chapter 1 to illustrate various points.