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Doing More With XML Schemas (part 1)
Learn to apply extensibility and inheritance to your schemas

| Keeping It Simple |

Let's begin with a quick refresher course in simple and complex element types. Consider the following XML document:


<?xml version="1.0" encoding="UTF-8"?>

<character>
<name>Luke Skywalker</name>
<species>Human</species>
<language>Basic</language>
<home>Tatooine</home>
</character>


The XML Schema specification makes a basic distinction between "simple" and "complex" elements. Simple elements cannot contain other elements or possess additional attributes; complex elements can have additional attributes and serve as containers for other elements (which themselves may be either simple or complex).

Within a schema, these two element types are represented by the <xsd:simpleType> and <xsd:complexType> elements respectively.

The easiest method to represent simple elements in a schema is to use the <xsd:element> declaration with a built-in datatype - the following simple element


<name>Luke Skywalker</name>


would be represented in a schema by


<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">;

<xsd:element name="name" type="xsd:string"/>

</xsd:schema>


When the datatype name is preceded by the "xsd:" prefix, it indicates a predefined datatype and not a new, user-defined type. The XML Schema specification lists about forty different built-in datatypes, including "string", "integer", "decimal", "float", "boolean", "time", "date", "dateTime" and "anyURI". However, in case these are too generic for you, it's also possible to derive your own custom datatype from the built-in ones, and then declare simple elements using this custom datatype.


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