Added unit tests for the event abstractions.
Added Element as the notion of common ancestry between Device and Host.
diff --git a/net/api/src/main/java/org/onlab/onos/net/HostLocation.java b/net/api/src/main/java/org/onlab/onos/net/HostLocation.java
new file mode 100644
index 0000000..5c124db
--- /dev/null
+++ b/net/api/src/main/java/org/onlab/onos/net/HostLocation.java
@@ -0,0 +1,17 @@
+package org.onlab.onos.net;
+
+/**
+ * Representation of a network edge location where an end-station host is
+ * connected.
+ */
+public interface HostLocation extends ConnectPoint {
+
+ /**
+ * Returns the timestamp when the location was established, given in
+ * milliseconds since start of epoch.
+ *
+ * @return timestamp in milliseconds since start of epoch
+ */
+ long timestamp();
+
+}