key and keyref

Given an XML such as:
<payroll>
  <depts>
    <hr location="Toronto"> ... </hr>
    <hr location="London"> ... </hr>
    <finance location="Toronto"> ... </finance>
    <finance location="New York"> ... </finance>
  </depts>

  <employees>
    <name="xxx">
      <dept>
        <name>hr</name>
        <location>London</location>
      </dept>
    </name>
    <name="xxxx"> ... </name>
  </employees>
</payroll>

In the above XML, the number of depts are known and limited to not more than
20.

In the schema, I have defined unique constaints on both hr and finance and
for other depts, if any:
    <xsd:unique name="HRKey">
      <xsd:selector xpath="/payroll/depts/hr" />
      <xsd:field xpath="@location" />
    </xsd:unique>
    <xsd:unique name="FinanceKey">
      <xsd:selector xpath="/payroll/depts/finance" />
      <xsd:field xpath="@location" />
    </xsd:unique>

Now, is it possible to create a key and keyref constaints so that
/payroll/employees/name/dept/name and 
/payroll/employees/name/dept/location are only pointing to:
/payroll/"any node()" and /payroll/"the node()"@location?


I understand that life will be much easier if I could rewrite the XML to:
<payroll>
  <depts>
    <dept name="hr" location="Toronto"> ... </dept>
    <dept name="hr" location="London"> ... </dept>
    <dept name="finance" location="Toronto"> ... </dept>
    <dept name="finance" location="New York"> ... </dept>
  </depts>
...
but I couldn't.

Thanks
Philip