QOF - The Query Object Framework is a C library that provides a query engine
to C applications. This allows SQL-like queries to be performes on a
collection of C/C++ objects (which act like SQL tables).
QOF is an offshoot of the GnuCash engine, consisting of those pieces
unrelated to accounting. The Query Engine allows C/C++ applications
to treat random collections of objects as if they were SQL tables,
and perform table-join type queries across them. In addition, the
query engine can be backed by an actual database, so that instances
of local objects can act as a 'cache' to a much larger SQL database.