Tuning the Conceptual Schema
The choice of conceptual schema should be guided by the workload, in addition to redundancy issues:
- We may settle for a 3NF schema rather than BCNF.
- Workload may influence the choice we make in decomposing a relation into 3NF or BCNF.
- We may further decompose a BCNF schema!
- We might denormalize (i.e., undo a decomposition step), or we might add fields to a relation.
- We might consider horizontal decompositions.
If such changes are made after a database is in use, called schema evolution; might want to mask some of these changes from applications by defining views.