However, the context space generated in Section 4.2 may be too sparse to find numbers in the database, especially when a query context is fine-grained.
when no item is retrieved for the query context, we employ a backoff strategy to drop some of the uninformative elements in the query context: elements are dropped from the context based on the type of argument, in this order: he (prep to), kara (prep from), ha (nsubj), yori (prep from), made (prep to), nite (prep at), de (prep at, prep by), ni (prep at), wo (dobj), ga (nsubj), and verb.