Uh, relational databases are a well established field. The different normal forms, among other useful things, provide a guide to way to prevent specific kinds of logical errors that can otherwise appear during inserts, updates and deletes. There's a lot here.

DRY - "don't repeat yourself" - is simply a slogan that doesn't provide specific procedures for making things compact, how you do it or when its appropriate. What you're saying is a lot like "abstract algebra is just a special case of thinking logically" - sort of true but mostly deceptive if it lets you dismiss a lot of accumulated knowledge with "just think logically".