Constraint within XML-Schema

Hi folks,

is it somehow possible to make sure that the amount of a certain element is equal to an attribute value ?

E.g. If the amount element is '4' there should be exactly 4 value elements within values. Is there a possibility
to realize this constraint in XML-Schema ?

<values amount="4"> 
  <value>1</value>
  <value>100</value>
  <value>23</value>
  <value>14</value>
</values>

Thanks in advance,

Uwe.