A wrapper generates an instance of this class to represent a
portion of the query fragment in a request that the data source can run. A
wrapper can generate several replies for a single Request.
The Reply
class adds methods and data members to:
- populate the reply by adding entries to the classes: add_to_CCCC
- store the execution descriptor pointer and size
- chain the replies when the wrapper returns more than one plan for the
same request
- store order information: interesting orderings of the returned data that
the optimizer might use to construct more optimal plan
