database-normalization

I understand the concept of database normalization, but always have a hard time explaining it in plain English - especially for a job interview. I have read the wikipedia post, but still find it hard to explain the concept to non-developers. "Design a database in a way not to get duplicated data" is the first thing that comes to mind. Does anyone has a nice way to explain the concept of database normalization in plain English? And what are some nice examples to show the differences between first, second and third normal forms? Say you go to a job interview and the person asks: Explain the

I have read the quote : data depends on the key [1NF], the whole key [2NF] and nothing but the key [3NF] . However, I am having trouble understanding 3.5NF or BCNF as it's called. Here is what I understand : BCNF is stricter than 3NF left side of any FD in the table must be a superkey (or at least a candidate key) So why is it then, that some 3NF tables are not in BCNF? I mean, the 3NF quote explicitly says "nothing but the key" meaning that all attributes depend solely on the primary key. The primary key is, after all, a candidate key until it is chosen to be our primary key. If anything is

I have always wondered how Facebook designed the friend <-> user relation. I figure the user table is something like this: user_email PK user_id PK password I figure the table with user's data (sex, age etc connected via user email I would assume). How does it connect all the friends to this user? Something like this? user_id friend_id_1 friend_id_2 friend_id_3 friend_id_N Probably not. Because the number of users is unknown and will expand. Keep a friend table that holds the UserID and then the UserID of the friend (we will call it FriendID). Both columns would be foreign keys back to the

I'm new in SQL(still learning) and I have to create a database for a venue. A client book for a room for an event. The problem is that the clients don't always provide their name, their email, and their phone number. Most of the time it's either name and email or name and phone. It's rarely all 3 but it happens. I need to store each of these in their respective attribute (name, email, phone). But the way they give me their info, I have a lot of null values. What can I do with these nulls? I've been told that it's better to not have nulls. I also need to normalize my table after that. Any