Codd’s 12 Rules
Learn how Codd’s 12 rules influence modern database design and implementation.
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Let’s dive into the foundational principles that define what a truly relational database is. In the early days of databases, many products claimed to be relational, but not all adhered to the same core principles. To clear up the confusion and establish a standard, the brilliant computer scientist Edgar F. Codd created a set of rules. Think of these rules as the official blueprint for a relational database, ensuring it's robust, consistent, and reliable. Understanding these rules helps us appreciate why modern databases work the way they do.
By the end of this lesson, we will be able to:
Understand the historical importance of Codd’s 12 Rules.
Identify and explain the key principles that define a true Relational Database Management System (RDBMS).
Recognize how these rules influence modern database design and implementation.
The story behind the rules
Before discussing the rules themselves, it is important to acknowledge their creator.
Edgar F. Codd, a researcher at IBM, published a landmark paper in 1970 introducing the relational model of data. Soon after, he observed that many database vendors were marketing their products as relational without fully adhering to the model’s principles.
To establish a clear benchmark, Codd formulated his well-known 12 rules—plus one foundational rule, bringing the total to 13—which became the gold standard for defining a genuine Relational Database Management System (RDBMS).
Although it is uncommon to find a DBMS that follows every rule precisely, these principles have shaped the design and evolution of nearly all relational databases in use today, including PostgreSQL and MySQL. Collectively, the rules function as a litmus test—the more completely a system conforms to them, the more authentically relational it is.
Codd’s 12 rules explained
Let’s go through each rule one by one, using our OnlineStore database to see them in action.