Visual Basic.NET How to Program (PDF)

Chapter 18 Extensible Markup Language (XML) 865
Fig. 18.15 XML Validator displaying an error message.
18.5.2 Microsoft XML Schemas
In this section, we introduce an alternative to DTDs—called Schemas—for defining XML
document structures. Many developers in the XML community feel that DTDs are not flexible
enough to meet today’s programming needs. For example, DTDs cannot be manipulated
(e.g., searched, programmatically modified, etc.) in the same manner that XML
documents can, because DTDs are not XML documents.
Unlike DTDs, Schemas do not use Extended Backus-Naur Form (EBNF) grammar.
Instead, Schemas are XML documents that can be manipulated (e.g., elements can be added
or removed, etc.) like any other XML document. As with DTDs, Schemas require validating
parsers.
In this section, we focus on Microsoft’s XML Schema vocabulary. 2 Figure 18.16 presents
an XML document that conforms to the Microsoft Schema document shown in
Figure 18.17. By convention, Microsoft XML Schema documents use the file extension
.xdr. Line 6 (Fig. 18.16) references the Schema document book.xdr.
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Fig. 18.16 XML document that conforms to a Microsoft Schema document (part 1 of 2).
2. For those readers who are interested in W3C Schema, we provide such examples on our Web site,
www.deitel.com. We also provide a detailed treatment of W3C Schema in XML How to Program,
2/e.