Enhanced cell & cells tools.
Provided initial sketch of the Annotated concept for the model attributes.
diff --git a/core/api/src/main/java/org/onlab/onos/net/Annotated.java b/core/api/src/main/java/org/onlab/onos/net/Annotated.java
new file mode 100644
index 0000000..f68cd46
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/net/Annotated.java
@@ -0,0 +1,25 @@
+package org.onlab.onos.net;
+
+import java.util.Set;
+
+/**
+ * Represents an entity that carries arbitrary annotations.
+ */
+public interface Annotated {
+
+ /**
+ * Returns the set of annotation keys currently available.
+ *
+ * @return set of annotation keys
+ */
+ Set<String> annotationKeys();
+
+ /**
+ * Returns the annotation value for the specified key.
+ *
+ * @param key annotation key
+ * @return annotation value; null if there is no annotation
+ */
+ String annotation(String key);
+
+}