2. The system of claim 1 wherein the nested data structure comprises an atom, a tuple, a map, and a bag, wherein the atom includes a single value, wherein the tuple includes a sequence of atoms, wherein the map includes a collection of key and value pairs, wherein the bag includes the collection of tuples.
2. The system of claim 1 wherein the nested data structure comprises an atom, a tuple, a map, and a bag, wherein the atom includes a single value, wherein the tuple includes a sequence of atoms, wherein the map includes a collection of key and value pairs, wherein the bag includes the collection of tuples. 4. The system of claim 2 wherein the stream of data comprises user activity logs, the user activity logs comprising a plurality of sessions, each session comprising a plurality of activities ordered by time, each session represented as an ordered bag identified by a session identifier.