attribute validation

hi there ,

   let me give an example ...
   
  <xs:attribute name="name" type="xs:string" use="required"/>
 
 the above example is definition of attribute element of an element called column.Since attribute name is required in every instance of column element it is defined as required.I want to know is it possible to validate this attribute value when it is assigned null value 
such as this
<column name =""/>  
I do not want any null values to be enrtered over there....at least some text string should be there ...so how to do this validation??????

regards,
rajendra