What is the Codd rule and how does it relate to RDBMS?

Answer

One joking version of this is: "The Key, the whole Key, and nothing but the Key, so help me CODD". Which means that any piece of data should be reliant on only one primary key in a table. Search the web for database design or data normalization or CODD or all of it. Alternately, try searching for Boyce-Codd Normal Form, which is a specific form of normalization for relational databases.

Answer

Edgar F Codd (considered to be the pioneer of the Relational Database Management System (RDBMS) concept) proposed 12 Rules (one could perhaps consider them as key characteristics) to determine if an RDBMS is truly an RDBMS.

From [1], and many other text-book sources (particularly those written by CJ Date):

1. Information Rule 2. Guaranteed Access Rule 3. Systematic Treatment of Null Values 4. Dynamic Online Catalog Based on the Relational Model 5. Comprehensive Data Sublanguage Rule 6. View Updating Rule 7. High-Level Insert, Update, and Delete 8. Physical Data Independence 9. Logical Data Independence 10. Integrity Independence 11. Distribution Independence 12. Nonsubversion Rule

Using these rules, there are actually very few systems which comes close to begin true RDBMSs

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