15.2.54. XML Schema union element

Element information ¶

父元素： SimpleType

Grammar ¶

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

(? The symbol declares that the element can appear zero or once in the union element. )

Attribute	Description
Id	Optional. Specifies the unique ID of the element.
MemberTypes	Optional. Specifies a list of names of built-in data types or simpleType elements defined in schema.
Any attributes	Optional. Specifies any other attributes with the non-schema namespace.

Example 1 ¶

This example is a simple type that combines 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>

In recent years, Geographic Information Systems (GIS) have undergone rapid development in both theoretical and practical dimensions. GIS has been widely applied for modeling and decision-making support across various fields such as urban management, regional planning, and environmental remediation, establishing geographic information as a vital component of the information era. The introduction of the “Digital Earth” concept has further accelerated the advancement of GIS, which serves as its technical foundation. Concurrently, scholars have been dedicated to theoretical research in areas like spatial cognition, spatial data uncertainty, and the formalization of spatial relationships. This reflects the dual nature of GIS as both an applied technology and an academic discipline, with the two aspects forming a mutually reinforcing cycle of progress.