Back in lesson one and two, one of the tables in the zoo database we talked about, was the diet table which describes which foods each species eats. We looked at three ways we could store multiple foods, for a single species. As multiple food columns and one row per species, as a single column with foods separated by commas. And has separate rows, for each food comma species pair and I mentioned that this form, has some big advantages over the other two. It works better with drawings, it works better in comparisons and you don't have to know in advance how many foods there are, and we also looked at these two tables of donors to the zoo and their phone numbers. In order to avoid duplication, we split the information that was in one object or it's record, into two separate tables. In database jargon, these are called normalized forms and the others are denormalized forms. Normalization is the central idea in database design. Normalizing involves making the relationships among the tables in your database, match the relationships that are really there amongst the various pieces of data. There's a bunch of database theory behind this idea. I put a link in the instructor notes to a paper with lots of details about it. Up ahead, I'll just tell you the most relevant highlights.