The relational model, on which all SQL DBMSs are based, is founded on both logic and sets. Relational operators like JOIN and UNION have a direct logical meaning, and you can use those operators to answer complex questions from your data unambiguously. Not only can you provide unambiguous answers, but you can translate SQL queries into the language of logic, which can be understood by people outside of IT.

Equally important is the utility of logic working backwards to help find meaning in disorganized (or perhaps undocumented) data sets. Nearly every inherited data set is less than perfectly documented, and often inconsistent. Changes to (or replacement of) the application require this data to be migrated. By iteratively making assertions and then testing them using the rules of logic and the convenience of sets, you can find exceptions and contradictions that help you refine the meaning of data, and possibly correct inconsistencies.

The talk will include SQL examples using a modified version of the Pagilla demonstration database (Pagilla: http://pgfoundry.org/projects/dbsamples/)