code: function purgeDependencies(unit, error, onPurgedDependentJoint, onDone){
  	db.takeConnectionFromPool(function(conn){
  		var arrQueries = [];
  		conn.addQuery(arrQueries, "BEGIN");
  		collectQueriesToPurgeDependentJoints(conn, arrQueries, unit, error, onPurgedDependentJoint, function(){
  			conn.addQuery(arrQueries, "COMMIT");
  			async.series(arrQueries, function(){
  				conn.release();
  				if (onDone)
  					onDone();
  			})
  		});
  	});
  }
docs: onPurgedDependentJoint called for each purged dependent unit