XML Schema How to Restrict Attribute by Enumeration

The numerical value seems to be missing from your price definition.Try the following:

<xs:simpleType name="curr">  <xs:restriction base="xs:string">    <xs:enumeration value="pounds" />    <xs:enumeration value="euros" />    <xs:enumeration value="dollars" />  </xs:restriction></xs:simpleType><xs:element name="price">        <xs:complexType>            <xs:extension base="xs:decimal">              <xs:attribute name="currency" type="curr"/>            </xs:extension>        </xs:complexType></xs:element>

New answer to old question

None of the existing answers to this old question address the real problem.

The real problem was that xs:complexType cannot directly have a xs:extension as a child in XSD. The fix is to use xs:simpleContent first. Details follow...

Your XML,

<price currency="euros">20000.00</price>

will be valid against either of the following corrected XSDs:

Locally defined attribute type

<?xml version="1.0" encoding="UTF-8"?><xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">  <xs:element name="price">    <xs:complexType>      <xs:simpleContent>        <xs:extension base="xs:decimal">          <xs:attribute name="currency">            <xs:simpleType>              <xs:restriction base="xs:string">                <xs:enumeration value="pounds" />                <xs:enumeration value="euros" />                <xs:enumeration value="dollars" />              </xs:restriction>            </xs:simpleType>          </xs:attribute>        </xs:extension>      </xs:simpleContent>    </xs:complexType>  </xs:element></xs:schema>

Globally defined attribute type

<?xml version="1.0" encoding="UTF-8"?><xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">  <xs:simpleType name="currencyType">    <xs:restriction base="xs:string">      <xs:enumeration value="pounds" />      <xs:enumeration value="euros" />      <xs:enumeration value="dollars" />    </xs:restriction>  </xs:simpleType>  <xs:element name="price">    <xs:complexType>      <xs:simpleContent>        <xs:extension base="xs:decimal">          <xs:attribute name="currency" type="currencyType"/>        </xs:extension>      </xs:simpleContent>    </xs:complexType>  </xs:element></xs:schema>

Notes

• As commented by @Paul, these do change the content type ofprice from xs:string to xs:decimal, but this is not strictlynecessary and was not the real problem.
• As answered by @user998692, you could separate out thedefinition of currency, and you could change to xs:decimal, butthis too was not the real problem.

The real problem was that xs:complexType cannot directly have a xs:extension as a child in XSD; xs:simpleContent is needed first.

A related matter (that wasn't asked but may have confused other answers):

How could price be restricted given that it has an attribute?

In this case, a separate, global definition of priceType would be needed; it is not possible to do this with only local type definitions.

How to restrict element content when element has attribute

<?xml version="1.0" encoding="UTF-8"?><xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">  <xs:simpleType name="priceType">      <xs:restriction base="xs:decimal">        <xs:minInclusive value="0.00"/>        <xs:maxInclusive value="99999.99"/>      </xs:restriction>    </xs:simpleType>  <xs:element name="price">    <xs:complexType>      <xs:simpleContent>        <xs:extension base="priceType">          <xs:attribute name="currency">            <xs:simpleType>              <xs:restriction base="xs:string">                <xs:enumeration value="pounds" />                <xs:enumeration value="euros" />                <xs:enumeration value="dollars" />              </xs:restriction>            </xs:simpleType>          </xs:attribute>        </xs:extension>      </xs:simpleContent>    </xs:complexType>  </xs:element></xs:schema>

you need to create a type and make the attribute of that type:

<xs:simpleType name="curr">  <xs:restriction base="xs:string">    <xs:enumeration value="pounds" />    <xs:enumeration value="euros" />    <xs:enumeration value="dollars" />  </xs:restriction></xs:simpleType>

then:

<xs:complexType>    <xs:attribute name="currency" type="curr"/></xs:complexType>