From http://www.w3schools.com (Copyright Refsnes Data)

XML Schema simpleType Element

Definition and Usage

The simpleType element defines a simple type and specifies the constraints and information about the values of attributes or text-only elements.

Element Information

Parent elements: attribute, element, list, restriction, schema, union

Syntax

<simpleType
id=ID
name=NCName
any attributes
>

(annotation?,(restriction|list|union))

</simpleType>

(The ? sign declares that the element can occur zero or one time inside the simpleType element)

Attribute	Description
id	Optional. Specifies a unique ID for the element
name	Specifies a name for the element. This attribute is required if the simpleType element is a child of the schema element, otherwise it is not allowed
any attributes	Optional. Specifies any other attributes with non-schema namespace

Example 1

This example defines an element called "age" that is a simple type with a restriction. The value of age can NOT be lower than 0 or greater than 100:

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

Complete XML Schema Reference