通过XSD在XML中的唯一元素值

Question

I have a xsd which has to prevent duplicate values for an element. I tried various ways and was somehow missing to achieve unique constraint for an element.

In the below xml, i have xyz:interval element having duplicate values. How to avoid the duplication using unique tag?

I have tried using unique in below XSD, but was not able to achieve the same.

XSD:

<?xml version="1.0" encoding="utf-8" ?>
<xs:schema xmlns:xyz="http://www.example.com/schema/public/" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.example.com/schema/public/" version="1.0" xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:complexType name="Intervals">
    <xs:sequence>
        <xs:element name="interval" type="xs:int" maxOccurs="unbounded">
            <xs:unique name="alias_unique">
                <xs:selector xpath="supportedMeasurementIntervals" />
                <xs:field xpath="." />
            </xs:unique>
        </xs:element>
        <xs:element name="defaultInterval" type="xs:int" minOccurs="1" maxOccurs="1" />
    </xs:sequence>
</xs:complexType>
<xs:element name="NoOfPeriod" type="xs:int" />
<xs:element name="isPeriodSupported" type="xs:boolean" />
<xs:element name="MType">
    <xs:complexType mixed="true">
        <xs:sequence minOccurs="0">
            <xs:element name="SIntervals" type="xyz:Intervals" minOccurs="0" maxOccurs="1" />
        </xs:sequence>
        <xs:attribute name="id" type="xs:string" use="required" />
    </xs:complexType>
</xs:element>
<xs:group name="Child">
    <xs:sequence>
        <xs:element name="SIntervals" type="xyz:Intervals" minOccurs="1" maxOccurs="1" />
        <xs:element ref="xyz:NoOfPeriod" minOccurs="1" maxOccurs="1" />
        <xs:element ref="xyz:isPeriodSupported" minOccurs="1" maxOccurs="1" />
    </xs:sequence>
</xs:group>
<xs:element name="Parent">
    <xs:complexType>
        <xs:sequence>
            <xs:element name="Child" minOccurs="1" maxOccurs="1">
                <xs:complexType>
                    <xs:group ref="xyz:Child" />
                </xs:complexType>
            </xs:element>
            <xs:element name="MTypes" minOccurs="1" maxOccurs="1">
                <xs:complexType>
                    <xs:sequence>
                        <xs:element ref="xyz:MType" maxOccurs="unbounded" />
                    </xs:sequence>
                </xs:complexType>
            </xs:element>
        </xs:sequence>
    </xs:complexType>
</xs:element>
</xs:schema>

XML :

<?xml version="1.0" encoding="utf-8"?>
<xyz:Parent xmlns:xyz="http://www.example.com/schema/public/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.example.com/schema/public/">
    <xyz:Child>
        <xyz:SIntervals>
            <xyz:interval>1111</xyz:interval>
            <xyz:interval>1111</xyz:interval>
            <xyz:interval>1111</xyz:interval>
            <xyz:interval>9727</xyz:interval>
            <xyz:defaultInterval>504</xyz:defaultInterval>
        </xyz:SIntervals>
        <xyz:NoOfPeriod>4804</xyz:NoOfPeriod>
        <xyz:isPeriodSupported>1</xyz:isPeriodSupported>
    </xyz:Child>
    <xyz:MTypes>
        <xyz:MType id="string" />
        <xyz:MType id="string" />
        <xyz:MType id="string">
            <xyz:SIntervals>
                <xyz:interval>2222</xyz:interval>
                <xyz:interval>2222</xyz:interval>
                <xyz:defaultInterval>6631</xyz:defaultInterval>
            </xyz:SIntervals>
        </xyz:MType>
        <xyz:MType id="string" />
    </xyz:MTypes>
</xyz:Parent>

Answer 1

Actually, you could change the maxOccurs="1" instead of "unbounded" in your definition of Intervals .

    [.....]
    <xs:complexType name="Intervals">
        <xs:sequence>
              <xs:element name="interval" type="xs:int" maxOccurs="1">
    [.....]

---

EDIT (After the comment)

1. you have to put your defined the namespace in the xpath expression.
2. as said in the comment, the unique apply to the scope of the element . you defined it a level too low.

for example, you could define the uniqueness in the scope of the Child element like following:

<xs:group name="Child">
<xs:sequence>
    <xs:element name="SIntervals" type="xyz:Intervals" minOccurs="1" maxOccurs="1" >
        <xs:unique name="uniqueInterval">
            <xs:selector xpath="xyz:interval" />
            <xs:field xpath="." />
        </xs:unique>
    </xs:element>
    <xs:element ref="xyz:NoOfPeriod" minOccurs="1" maxOccurs="1" />
    <xs:element ref="xyz:isPeriodSupported" minOccurs="1" maxOccurs="1" />
</xs:sequence>

You'll then have to do it the same way for your other elements (or you re-design the definition).