<xs:schema
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    >

   <xs:attributeGroup name="AttrGroup">
       <xs:attribute name="attr1" type="xs:string"/>
        <xs:attribute name="attr2" type="xs:int"/>
        <xs:attribute name="attr3" type="xs:string"/>
   </xs:attributeGroup>
</xs:schema>