Re-assembled the topology subsystem.
diff --git a/core/api/src/main/java/org/onlab/onos/net/topology/TopologyProviderService.java b/core/api/src/main/java/org/onlab/onos/net/topology/TopologyProviderService.java
index 0e03767..c81a871 100644
--- a/core/api/src/main/java/org/onlab/onos/net/topology/TopologyProviderService.java
+++ b/core/api/src/main/java/org/onlab/onos/net/topology/TopologyProviderService.java
@@ -10,16 +10,13 @@
  */
 public interface TopologyProviderService extends ProviderService<TopologyProvider> {
 
-    // What can be conveyed in a topology that isn't by individual
-    // providers?
-
     /**
      * Signals the core that some aspect of the topology has changed.
      *
-     * @param topoDescription information about topology
-     * @param reasons         events that triggered topology change
+     * @param graphDescription information about the network graph
+     * @param reasons          events that triggered topology change
      */
-    void topologyChanged(TopologyDescription topoDescription,
+    void topologyChanged(GraphDescription graphDescription,
                          List<Event> reasons);
 
 }