Unique element in XSD sequence

Question

I'd like to have an XSD to valide an XML containing file elements with many aliases but each alias with a different value.

This is my XML:

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<folder>
  <files>
    <fileList>
      <file>
        <title>Document1</title>
        <fileAlias>
          <alias>Alias1</alias>
          <alias>Alias2</alias>
        </fileAlias>
      </file>
    </fileList>
  </files>
</folder>

The former XML is good because Alias1 != Alias2

How could I specify it in my XSD:

<?xml version="1.0" encoding="utf-8"?>
<xs:schema attributeFormDefault="unqualified" elementFormDefault="qualified" version="1.0"
           xmlns:xs="http://www.w3.org/2001/XMLSchema">
  <xs:element name="folder" type="folderType" />
  <xs:complexType name="folderType">
    <xs:sequence>
      <xs:element name="files" type="filesType" />
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="filesType">
    <xs:sequence>
      <xs:element name="fileList" type="fileListType" />
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="fileListType">
    <xs:sequence>
      <xs:element maxOccurs="unbounded" name="file" type="fileType" />
    </xs:sequence>
  </xs:complexType>
  <xs:complexType name="fileType">
    <xs:sequence>
      <xs:element name="title" type="xs:string" />
      <xs:element name="fileAlias" type="fileAliasType" minOccurs="0" maxOccurs="unbounded" />
    </xs:sequence>
    <xs:attribute name="id" type="xs:string" />
    <xs:attribute name="type" type="xs:int" />
  </xs:complexType>
  <xs:complexType name="fileAliasType">
    <xs:sequence>
      <xs:element maxOccurs="unbounded" name="alias" type="xs:string" minOccurs="1" />
    </xs:sequence>
  </xs:complexType>
</xs:schema>

I've tried with xsd:unique but I think is for attributes not for XML element text values.

Answer 1

If I understand well your need then xs:unique should be the right way. Following modification of fileType complex type should be enough.

<xs:complexType name="fileType">
    <xs:sequence>
        <xs:element name="title" type="xs:string"/>
        <xs:element name="fileAlias" type="fileAliasType" minOccurs="0" maxOccurs="unbounded">
            <xs:unique name="alias_unique">
                <xs:selector xpath="alias"/>
                <xs:field xpath="."/>
            </xs:unique>
        </xs:element>
    </xs:sequence>
    <xs:attribute name="id" type="xs:string"/>
    <xs:attribute name="type" type="xs:int"/>
</xs:complexType>

This will validate

<?xml version="1.0" encoding="UTF-8"?>
<!--Sample XML file generated by XMLSpy v2013 sp1 (http://www.altova.com)-->
<folder xsi:noNamespaceSchemaLocation="unique.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <files>
        <fileList>
            <file id="String" type="0">
                <title>String</title>
                <fileAlias>
                    <alias>String1</alias>
                    <alias>String2</alias>
                    <alias>String3</alias>
                </fileAlias>
            </file>
        </fileList>
    </files>
</folder>

This won't

<?xml version="1.0" encoding="UTF-8"?>
<!--Sample XML file generated by XMLSpy v2013 sp1 (http://www.altova.com)-->
<folder xsi:noNamespaceSchemaLocation="unique.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <files>
        <fileList>
            <file id="String" type="0">
                <title>String</title>
                <fileAlias>
                    <alias>String1</alias>
                    <alias>String1</alias>
                    <alias>String3</alias>
                </fileAlias>
            </file>
        </fileList>
    </files>
</folder>