+ /**
+ * Populates <tt>rulesDB</tt> with rules specifying how to reach
+ * <tt>host</tt> from <tt>currNode</tt> assuming that:
+ * <ul>
+ * <li><tt>host</tt> is attached to <tt>rootNode</tt>
+ * <li><tt>link</tt> is the next part of the path to reach <tt>rootNode</tt>
+ * from <tt>currNode</tt>
+ * <li><tt>rulesDB.get(key)</tt> represents the list of rules stored about
+ * <tt>host</tt> at <tt>currNode</tt>
+ * </ul>
+ *
+ * @param host
+ * The host to be reached.
+ * @param currNode
+ * The current node being processed.
+ * @param rootNode
+ * The node to be reached. Really, the switch which host is
+ * attached to.
+ * @param link
+ * The link to follow from curNode to get to rootNode
+ * @param key
+ * The key to store computed rules at in the rulesDB. For now,
+ * this is a {@link HostNodePair} of host and currNode.
+ */