7. The system of claim 1 , wherein the operations further comprise: generating an execution tree based on a sequence of tokens, the execution tree including a plurality of nodes, a node of the execution tree being associated with one or more tokens; and associating the execution tree with a current version identifier of the token database.
7. The system of claim 1 , wherein the operations further comprise: generating an execution tree based on a sequence of tokens, the execution tree including a plurality of nodes, a node of the execution tree being associated with one or more tokens; and associating the execution tree with a current version identifier of the token database. 10. The system of claim 7 , wherein the operations further comprise: converting text of a database request into the sequence of tokens and an unknown word; and generating the execution tree based on the sequence of tokens and the unknown word, a node of the execution tree being associated with the unknown word.