This is w.r.t Database Normalisation, when I have a redundant table that causes anomalies, I would want to consider splitting it in smaller tables as per the NF rules.
Say I split a big table into two eg. Student and Marks Table my questions is ---
How do I know I've done the right split?
Or to put it in another way,
How can I cross check if I haven't lost any information after the split i.e. I can still do a join on both tables and get my un-normalized table back?
This is easy to inspect visually when you have a small number of attributes, but what if the table is really huge.
How can I ensure that I've split the table in a right manner?
When I was in college my professor spoke of some equation which must always be true whenever you split tables, that ensures that the split is done without loss of any information. And by doing the right joins we can get the big dirty redundant table back.