isMemberf

$boolean = $session->isMemberf( $object1, $relation,
     $object2, $freshness )

The isMemberf() function returns TRUE if $object2 is a member of the specified $object1 relationship. If the $relation is a computed or polled value and is more than $freshness seconds old, it is refreshed first. The section “$freshness” on page 73 provides additional information.

 $flag = $session->isMemberf( "Router::strrtbos",
     "ComposedOf",
     "Interface::IF-strrtbos/1",
     240 );