Data types in XML Schema (XSD)

XML Schema defines the structure and data types of an XML document. Types are either simple or complex.

1. Simple types

A simple type holds only text/data. It has no child elements and no attributes.

Built-in simple types: xs:string, xs:integer, xs:decimal, xs:boolean, xs:date, xs:time, xs:float.

<xs:element name="name"  type="xs:string"/>
<xs:element name="age"   type="xs:integer"/>
<xs:element name="dob"   type="xs:date"/>

Matching XML: <name>Ravi</name> <age>21</age> <dob>2004-05-12</dob>

User-defined simple type (restriction):

<xs:simpleType name="marksType">
  <xs:restriction base="xs:integer">
    <xs:minInclusive value="0"/>
    <xs:maxInclusive value="100"/>
  </xs:restriction>
</xs:simpleType>
<xs:element name="marks" type="marksType"/>

Simple types can also be created as a list or union of other types.

2. Complex types

A complex type may contain child elements, attributes, or both, so it describes structured data.

<xs:element name="student">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="name"  type="xs:string"/>
      <xs:element name="age"   type="xs:integer"/>
      <xs:element name="marks" type="xs:integer"/>
    </xs:sequence>
    <xs:attribute name="roll" type="xs:string" use="required"/>
  </xs:complexType>
</xs:element>

Matching XML:

<student roll="CS101">
  <name>Ravi</name>
  <age>21</age>
  <marks>88</marks>
</student>

Content models: xs:sequence (fixed order), xs:choice (one of several), xs:all (any order). Complex types can also mix text and elements (mixed="true") or be empty with only attributes.

Comparison

Feature	Simple type	Complex type
Child elements	No	Yes
Attributes	No	Yes
Content	Text value only	Elements, attributes, or both
Example	<age>21</age>	<student roll="1">...</student>
Reuse	Named simpleType	Named complexType

Note that an attribute itself always has a simple type.