What are Abstract Query Plans in Sybase ASE?

An abstract plan is a description of a query plan which is kept
in persistent storage, can be read and edited, and is associated with
a specific query. When executing that query, the optimizer's plan
will be based on the information in the abstract plan. The abstract
plan may provide partial information, for example it may merely
specify an index to use; or, it may provide the full query plan
used to execute the query.