Extensible Schema Definitions (XSD) are used to define the legal building blocks of an XML document. XSD is actually an XML based meta-language used to:

1. Define the elements that can appear in an XML Document
2. Define attributes that can appear in an XML Document
3. Define the child elements and their relationships within an XML Document

All XSD schemas contain a single top level element. Underneath this element is the schema element that contains either simple or complex type elements. Simple elements contain text only information. Complex elements are a grouping element that acts as a container for other elements and attributes. There are four types of complex elements – empty elements, elements that contain other elements, elements that contain only text and elements that contain both other elements and text.

Here is an example of an XSD that defines a schema structure that represents a customer record.

<?xml version="1.0"?>

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

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

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

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

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

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

<xsd:element name="mail1" type="xsd:string"/>

<xsd:element name="mail2" type="xsd:string"/>

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

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

<xsd:element name="entereddate" type="xsd:date"/>

<xsd:element name="customerinfo">

<xsd:complexType>

      <xsd:sequence>

            <xsd:element ref="prefix"  minOccurs="0"/>

            <xsd:element ref="firstname"/>

            <xsd:element ref="lastname"/>

            <xsd:element ref="suffix" minOccurs="0"/>

            <xsd:element ref="email"/>

            <xsd:element ref="mail1"/>         

            <xsd:element ref="mail2"/>         

            <xsd:element ref="mailstate"/>           

            <xsd:element ref="mailzip"/>       

            <xsd:element ref="entereddate"/>         

      </xsd:sequence>

</xsd:complexType>

</xsd:element>

</xsd:schema>

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