This module provides an object that matches a data source against a
query expression.

Query expressions are compiled into an internal form when a new object
is created or the `prepare' method is called; they are not recompiled on
each match.

The class provided by this module uses four packages to process the
query. The query parser parses the question and calls a query expression
builder (internal form of the question). The optimizer is then called to
reduce the complexity of the expression. The solver applies the
expression on a data source.