Designing a schema for your relational database is a daunting task that has long term implications for the database's performance, maintainability, and correctness. And it often requires making decisions before having a clear picture of the exact shape and distribution of your data, or what the common access patterns will look like. It's not a permanent decision: tables can be altered and databases migrated. But these migrations can be slow and expensive. To top it all off, some data is less ame...