Re-assembled the topology subsystem.
diff --git a/core/api/src/main/java/org/onlab/onos/net/Path.java b/core/api/src/main/java/org/onlab/onos/net/Path.java
index 22a363a..acf8170 100644
--- a/core/api/src/main/java/org/onlab/onos/net/Path.java
+++ b/core/api/src/main/java/org/onlab/onos/net/Path.java
@@ -17,4 +17,11 @@
      */
     List<Link> links();
 
+    /**
+     * Returns the path cost as a unit-less value.
+     *
+     * @return unit-less path cost
+     */
+    double cost();
+
 }