Required field in XSD file

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XML

Dear Comrades,
I want to check element as required in schema file, the below code is my schema file and i tried to check required for Country, but it not working, please tell me how,

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" attributeformdefault="unqualified" elementformdefault="qualified">
<xs:element name="shiporder">
<xs:complextype>
<xs:sequence>
<xs:element type="xs:string" name="orderperson" />
<xs:element name="shipto">
<xs:complextype>
<xs:sequence maxoccurs="unbounded" minoccurs="1">
<xs:element type="xs:string" name="name" />
<xs:element type="xs:string" name="address" />
<xs:element type="xs:string" name="city" />
<xs:element type="xs:string" name="country" minoccurs="1" />
</xs:sequence>
</xs:complextype>
</xs:element>
<xs:element name="item" maxoccurs="unbounded" minoccurs="0">
<xs:complextype>
<xs:sequence>
<xs:element type="xs:string" name="title" />
<xs:element type="xs:string" name="note" minoccurs="0" />
<xs:element type="xs:byte" name="quantity" />
<xs:element type="xs:float" name="price" />
</xs:sequence>
</xs:complextype>
</xs:element>
</xs:sequence>
<xs:attribute type="xs:int" name="orderid" use="required" />
</xs:complextype>
</xs:element>
</xs:schema>