In an ideal world (still looking for it) you would design all your databases from a model, using a good tool, my preference Power Designer (Sybase). Then apply all changes to the model first, so you would always have an accurate model of your database and you could always see what would be impacted when changing your database. The model would end up generating the documentation and data dictionary.

Unfortunately it never seems to work that way anymore, business want change to happen far to quickly, so they just rush into the development not taking the time and effort to put down the ground work in the design stage. They always end up paying the price later, but then that comes out of a different budget.