Codd's 12 rules

Imagine you have a bunch of toys in your room that you want to store in an organized way. You can't just throw them all on the floor and hope they don't get lost or mixed up. You need to follow certain rules to make sure each toy has a proper place and can be found easily when you want to play with it. That's kind of what Codd's 12 Rules are all about, but instead of toys, it's about how to organize and store data in a computer system.

1. Rule 1: The Information Rule - This means that all data should be stored in one place and not duplicated. It's like having one toy box instead of two, so you always know where to find what you're looking for.

2. Rule 2: The Guaranteed Access Rule - This means that all data must be accessible by everybody who has permission to see it. It's like sharing your toys with your friends so they can play with them too.

3. Rule 3: The Systematic Treatment of Null Values - This is about how to deal with missing data. It's like if you lost a toy and you want to make sure you find it again, you need to take extra care to look for it.

4. Rule 4: The Dynamic Online Catalog Rule - This means that there must be a way to see what data is stored in the system at any given time. It's like having a list of all your toys and where you put them, so you can quickly find them when you need them.

5. Rule 5: The Comprehensive Data Sublanguage Rule - This means that there should be a way to talk about the data that everyone can understand. It's like using simple words to describe your toys so your friends know exactly what you're talking about.

6. Rule 6: The View Updating Rule - This means that if a change is made to the data, it should be updated everywhere it's being used. It's like if you change your mind about where to put your toy, you need to move it to the new spot so you always know where it is.

7. Rule 7: The High-Level Insert, Update, and Delete Rule - This means that any changes to the data should be easy to make and not require a lot of extra work. It's like moving your toys around without having to take everything out of the toy box first.

8. Rule 8: The Physical Data Independence Rule - This means that the data should be stored in a way that doesn't depend on the hardware or software being used. It's like being able to move all your toys from one room to another without having to worry about whether they will fit or not.

9. Rule 9: The Logical Data Independence Rule - This means that the way the data is organized should not depend on how it will be used. It's like having a system for organizing your toys that works no matter how you want to play with them.

10. Rule 10: The Integrity Independence Rule - This means that the accuracy and consistency of the data should not depend on anything else. It's like knowing that your toy is still in the same spot even if Mom or Dad moved some other toys around.

11. Rule 11: The Distribution Independence Rule - This means that the data should be available no matter where it's needed or used. It's like being able to bring your toys with you wherever you go, and still having access to them when you want to play.

12. Rule 12: The Non-Subversion Rule - This means that nobody should be able to bypass any of the rules to get access to the data. It's like making sure that all your friends play by the same rules when they come over to play with your toys.