$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 );