September 30, 2010
The previous post about Boolean datatype sparkled a lively discussion at comp.databases.theory. Here, I’ll embark upon Tony Andrews comment that SQL DBMS world somehow abhors unary relations. This is very strange from theoretical perspective, as one can expect lower arity relations be prevalent according to Zipf law.
This is one more artifact of infamous impedance mismatch between front-end application and DBMS. The client behavior is imperative: “Tell me if my customer is creditworthy or not, so I can proceed with her application. (I don’t care about the list of all other creditworthy customers!)” . It clearly wants a boolean answer. What database reply might be? “Look, I supplied all the [relevant] information, isn’t decision and taking action your responsibility?”
P.S. We all know that ORM tools (Hibernate, Linq, etc) solved impedance problem already, so the issue is no longer there! Just kidding.