define function snapshot( $e, $ts, $te )  {
  if (($e/date(@tstart) <= date($ts)) and
      ($e/date(@tend) >= date($ts)) and
      ($e/date(@tend) <= date($te)))
  then (
     element mgrno {
	attribute tstart{$ts},
	attribute tend{$e/@tend},
	$e/text()
     }
  )
  else if (($e/date(@tend) >= date($te)) and
      ($e/date(@tstart) >= date($ts)) and
      ($e/date(@tstart) <= date($te)))
  then (
     element mgrno {
	attribute tstart{$e/@tstart},
	attribute tend{$te},
	$e/text()
     }
  )
  else if (($e/date(@tstart) >= date($ts)) and
      ($e/date(@tend) <= date($te)))
  then (
     element mgrno {
	attribute tstart{$e/@tstart},
	attribute tend{$e/@tend},
	$e/text()
     }
  )
  else if (($e/date(@tstart) <= date($ts)) and
      ($e/date(@tend) >= date($te)))
  then (
     element mgrno {
	attribute tstart{$ts},
	attribute tend{$te},
	$e/text()
     }
  )
  else ()
}

for $y in document('v-depts.xml')/departments/department
return element department{$y/deptno, 
for $x in $y/mgrno
return snapshot($x, '1994-05-06', '1995-05-06')}