XML in a Nutshell, 3rd Edition

Element Declarations

XML documents are composed primarily of nested elements, and xs:element is one of the most often used declarations in a typical schema. This simple example schema already includes a single global element declaration that tells the schema processor that instance documents must consist of a single element, fullName:

<xs:element name="fullName" type="xs:string">

This declaration uses two attributes to describe the element that can appear in the instance document: name and type. The name attribute is self-explanatory, but the type attribute requires some additional explanation.

Simple types

Schemas support two different types of content: simple and complex. Simple content consists of pure text that does not contain nested elements.

In the previous example, the type="xs:string" attribute tells the schema processor that this element can only contain simple content of the built-in type xs:string. Table 17-1 lists a representative sample of the built-in simple types that are defined by the schema specification. See Chapter 22 for a complete listing.

Table 17-1. Built-in simple schema types

Type	Description
anyURI	A Uniform Resource Identifier
base64Binary	Base64-encoded binary data
boolean	May contain either true or false, 0 or 1
byte	A signed byte quantity >= -128 and <= 127
dateTime	An absolute date and time
duration	A length of time, expressed in units of years, months, days, hours, etc.
ID, IDREF, IDREFS, ENTITY, ENTITIES, NOTATION, NMTOKEN, NMTOKENS	Same values as ...