Question

How to prohibit duplicate tag in my restriction tag in my xml file?
for example in my xml file I have two locale tag,but it should be only one tag

this is my xml file :

    <app:string name="firstName">
        <app:restriction>
            <app:regex>^\w*$</app:regex>
            <app:type/>
            <app:locale/>
            <app:locale/>
        </app:restriction>
    </app:string>

and this is my xsd for string tag:

<xs:element name="string">
    <xs:complexType>
        <xs:complexContent>
            <xs:extension base="main:BaseType">
                <xs:sequence>
                    <xs:element name="restriction" type="main:StringRestriction" minOccurs="0"
                                maxOccurs="1"/>
                </xs:sequence>
                <xs:attribute name="lang" type="main:LocaleTypes"/>
            </xs:extension>
        </xs:complexContent>
    </xs:complexType>
</xs:element>

<xs:complexType name="BaseType">
    <xs:attribute name="name" type="main:nameType" use="required"/>
    <xs:attribute name="readonly" type="xs:boolean" use="optional" default="true"/>
</xs:complexType>

<xs:complexType name="StringRestriction">
    <xs:complexContent>
        <xs:extension base="main:RestrictionBase">
            <xs:sequence>
                <xs:choice maxOccurs="1">
                    <xs:element type="xs:string" name="locale"/>
                    <xs:element type="xs:string" name="type"/>
                    <xs:element type="xs:string" name="regex"/>
                    <xs:element type="xs:string" name="maxLen"/>
                    <xs:element type="xs:string" name="minLen"/>
                </xs:choice>
            </xs:sequence>
        </xs:extension>
    </xs:complexContent>
</xs:complexType>

Answer 1

If I correctly understood you need a schema that force your restriction tag to contain tags without repetitions.

if you substitute this:

<xs:sequence>
    <xs:choice maxOccurs="1">
        <xs:element type="xs:string" name="locale"/>
        <xs:element type="xs:string" name="type"/>
        <xs:element type="xs:string" name="regex"/>
        <xs:element type="xs:string" name="maxLen"/>
        <xs:element type="xs:string" name="minLen"/>
    </xs:choice>
</xs:sequence>

with this:

<xs:all minOccurs="0">
    <xs:element type="xs:string" name="locale"/>
    <xs:element type="xs:string" name="type"/>
    <xs:element type="xs:string" name="regex"/>
    <xs:element type="xs:string" name="maxLen"/>
    <xs:element type="xs:string" name="minLen"/>
</xs:all>

your schema won’t allow duplicated locale elements inside your restriction tag.
You can see a summary here: http://www.w3schools.com/schema/el_all.asp
Beside this, you can play with minOccurs and maxOccurs to force some elementes to always appear and other to be just optional.