Sunday, August 25, 2019

Meaning Criteria and Entity Supertype-Subtypes Relationships

Note: This is a re-write of a previous post.
"I have a database for a school ... [with] numerous tables obviously, but consider these:
CONTACT - all contacts (students, faculty): has fields such as LAST, FIRST, ADDR, CITY, STATE, ZIP, EMAIL;
FACULTY - hire info, login/password, foreign key to CONTACT;
STUDENT - medical comments, current grade, foreign key to CONTACT."
"Do you think it is a good idea to have a single table hold such info? Or, would you have had the tables FACULTY and STUDENT store LAST, FIRST, ADDR and other fields? At what point do you denormalize for the sake of being more practical? What would you do when you want to close out one year and start a new year? If you had stand-alone student and faculty tables then you could archive them easily, have a school semester and year attached to them. However, as you go from one year to the next information about a student or faculty may change. Like their address and phone for example. The database model now is not very good because it doesn’t maintain a history. If Student A was in school last year as well but lived somewhere else would you have 2 contact rows? 2 student rows?  Or do you have just one of each and have a change log. Which is best?"
How would somebody who "does not know past, or new requirements, modeling, and database design" and messes with a working database just because "he heard something about (insert your favorite fad here)" figure out correct from bad answers? Particularly if the answers suffer from the same lack of foundation knowledge as the question?