Sebastopol, CA--Theory is practical. This is an article of faith with well-known author and database authority Chris Date. "I mention this point explicitly because so many people seem to believe the exact opposite: namely, that if something's theoretical, it can't be practical," he explains. "But the truth is that theory--at least the theory I'm talking about here, which is relational theory--is most definitely very practical indeed." Relational theory is not just theory for its own sake, Date observes; the purpose of that theory is to allow people to build systems that are one hundred percent practical.