Using unique element in XML scheme

Question

I'm trying to use unique element to ensure uniqueness of one of the attributes. Attribute cisloStavu of element stav that I want to be unique has the same value for it's two instances, but validator say's it's OK. I have read many guides about this, and now I'm quite confused, because it looks like I do it the right way.

Here is my XML file (important lines are commented):

<?xml version="1.0" encoding="UTF-8"?>
<Automat nazevKrizovatky="" xmlns="urn:x-fido:schemata:automat-severka" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:x-fido:schemata:automat-severka automat.xsd ">
  <stav cisloStavu="0" interval="0">                    <-- first occurence of cisloStavu="0" -->
    <nasledujiciStav>0</nasledujiciStav>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
  </stav>
  <stav cisloStavu="0" interval="0">               <-- second occurence of cisloStavu="0" -->
    <nasledujiciStav>0</nasledujiciStav>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semafor cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
    <semaforProChodce cisloSemaforu="0" stavSemaforu="zelena"/>
  </stav>
</Automat>

and here is the scheme:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema  targetNamespace="urn:x-fido:schemata:automat-severka" 
            elementFormDefault="qualified" 
            xmlns:xs="http://www.w3.org/2001/XMLSchema" 
            xmlns="urn:x-fido:schemata:automat-severka">



    <xs:simpleType name="intervalType">
        <xs:restriction base="xs:nonNegativeInteger"></xs:restriction>
    </xs:simpleType>

    <xs:simpleType name="cisloStavuType">
        <xs:restriction base="xs:nonNegativeInteger"></xs:restriction></xs:simpleType>

    <xs:simpleType name="nasledujiciStavType">
        <xs:restriction base="xs:nonNegativeInteger"></xs:restriction>
    </xs:simpleType>

    <xs:complexType name="StavType">
        <xs:sequence>
            <xs:element name="nasledujiciStav" type="nasledujiciStavType" minOccurs="1" maxOccurs="unbounded">
            </xs:element>
            <xs:element name="semafor" type="semaforType" minOccurs="8" maxOccurs="8">
            </xs:element>
            <xs:element name="semaforProChodce" type="semaforProChodceType" minOccurs="8" maxOccurs="8"></xs:element>
        </xs:sequence>
        <xs:attribute name="cisloStavu" type="cisloStavuType" use="required"></xs:attribute>
        <xs:attribute name="interval" type="intervalType" use="required"></xs:attribute>
    </xs:complexType>

    <xs:complexType name="AutomatType">
        <xs:sequence>
            <xs:element name="stav" type="StavType" maxOccurs="unbounded"></xs:element>
        </xs:sequence>
        <xs:attribute name="nazevKrizovatky" type="nazevKrizovatkyType" use="required"></xs:attribute>
    </xs:complexType>

    <xs:element name="Automat" type="AutomatType">
        <xs:unique name="unikatni_stav">            <-- unique element -->
            <xs:selector xpath="stav" />
            <xs:field xpath="@cisloStavu" />
        </xs:unique>
    </xs:element>

    <xs:simpleType name="nazevKrizovatkyType">
        <xs:restriction base="xs:string"></xs:restriction>
    </xs:simpleType>


    <xs:simpleType name="cisloSemaforuType">
        <xs:restriction base="xs:nonNegativeInteger"></xs:restriction></xs:simpleType>

    <xs:simpleType name="stavSemaforuType">
        <xs:restriction base="xs:string">
            <xs:enumeration value="zelena"></xs:enumeration>
            <xs:enumeration value="červena"></xs:enumeration>
            <xs:enumeration value="pozorZelena"></xs:enumeration>
            <xs:enumeration value="pozorČervena"></xs:enumeration>
            <xs:enumeration value="zelenaVprvavo"></xs:enumeration>
        </xs:restriction>
    </xs:simpleType>

    <xs:complexType name="semaforType">
        <xs:attribute name="cisloSemaforu" type="cisloSemaforuType" use="required"></xs:attribute>
        <xs:attribute name="stavSemaforu" type="stavSemaforuType" use="required"></xs:attribute>
    </xs:complexType>

    <xs:complexType name="semaforProChodceType">
        <xs:attribute name="cisloSemaforu" type="cisloSemaforuType" use="required"></xs:attribute>
        <xs:attribute name="stavSemaforu" type="stavSemaforuProChodceType" use="required"></xs:attribute>
    </xs:complexType>

    <xs:simpleType name="stavSemaforuProChodceType">
        <xs:restriction base="xs:string">
            <xs:enumeration value="zelena"></xs:enumeration>
            <xs:enumeration value="červena"></xs:enumeration>
        </xs:restriction>
    </xs:simpleType>
</xs:schema>

Answer 1

Finally I've found the problem. I used default namespace (not to be confused with no namespace), and I forgot that xpath expressions (that is in unique element) ignore default namespace. In other words default namespace elements can't be reached by xpath expression.

I added the prefix to namespace in XML and also to xpath expression in unique element, and now it works fine!