XML data structure like 'Multiple selection'

Question

Hello. I wonder how i could easily describe Multiple selection combobox using XML and Schema. Currently iam using this definition:

<xs:element name="RefPartner">
 <xs:complexType>
  <xs:attribute name="isSalesRepresentative" type="xs:boolean"/>
  <xs:attribute name="isPolicyResponsible" type="xs:boolean"/>
  <xs:attribute name="isPolicyCorrespondanceResponcible" type="xs:boolean"/>
  <xs:attribute name="isAssetManager" type="xs:boolean"/>
  <xs:attribute name="isContactPerson" type="xs:boolean"/>
  <xs:attribute name="isLegalRepresentative" type="xs:boolean"/>
 </xs:complexType>

but this solution is no good. Please write your ideas, how to make this better. Thanks.