# XML Schema union Element

Complete XML Schema Reference

## Definition and Usage

The union element defines a simple type as a collection (union) of values from specified simple data types.

### Element Information

- Parent elements: simpleType

### Syntax

<union
id=ID
memberTypes="list of QNames"
any attributes
>
(annotation?,(simpleType*))
</union>

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

Attribute | Description
--- | ---
id | Optional. Specifies a unique ID for the element
memberTypes | Optional. Specifies a list of built-in data types or simpleType elements defined in a schema
any attributes | Optional. Specifies any other attributes with non-schema namespace

### Example 1

This example shows a simple type that is a union of two simple types:

<xs:element name="jeans_size">
<xs:simpleType>
<xs:union memberTypes="sizebyno sizebystring" />
</xs:simpleType>
</xs:element>
<xs:simpleType name="sizebyno">
<xs:restriction base="xs:positiveInteger">
<xs:maxInclusive value="42"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="sizebystring">
<xs:restriction base="xs:string">
<xs:enumeration value="small"/>
<xs:enumeration value="medium"/>
<xs:enumeration value="large"/>
</xs:restriction>
</xs:simpleType>

Complete XML Schema Reference

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