The 'key' in this case is what the tag or value is attached to, not the context of the value. So in your example, all the "pet" values would be stored together within the KV store just like values in a relational table column. Likewise all the "program" values would be stored together within a different KV store.

So some typical queries might be: Find all the photos where "Event" = "Wedding" Find all rows where "State" = "California"

The keys in this case would be the IDs of the photos or the row keys in the relational table.