Why Are E.F. Codd's 13 Rules Often Cited as 12, and the Importance of Rule Zero

When discussing the foundational principles of relational database management systems (RDBMS), one often encounters the name of E.F. Codd and a list of twelve rules. However, these twelve rules are often based on the original thirteen that Codd proposed. This article explores the history behind these rules, the significance of Rule Zero, and why there is a discrepancy in the number of rules mentioned.

Understanding E.F. Codd and His Contributions to Database Management

E.F. Codd was a British computer scientist at IBM Research during the 1970s. He is widely recognized as the father of relational database theory. His seminal paper titled “A Relational Model of Data for Large Shared Data Banks” was published in 1970. In this paper, Codd presented a series of rules or principles that defined a truly relational database management system. These rules laid the groundwork for the modern database systems we use today.

The Thirteen Original Rules

Codd proposed thirteen rules to evaluate the relational nature of a database management system. These rules were as follows:

It must support table-wide relations Access must not depend on the query form Entity integrity must be preserved Referential integrity must be preserved Informational independence: Logical independence, Physical independence Every relational operation is free to act on any subset of the relations and any combination of attributes Naming can be based on the schema Access can be based on the structure or content of the data, not on the physical implementation The system must support a procedural language for natural and efficient implementation of large applications The system must be capable of supporting extensible data types A user must be allowed to redefine his or her own schema without reprogramming of applications All language capabilities should be supported by the system, not by add-ons The system must not impose an integrity constraint or information type on a database unless that constraint is optional and obeyed by the system itself, i.e., the system should hide data dictionary information

While Rule Zero is not one of the original thirteen, it has emerged as a foundational concept that is inseparable from the original rules. This rule, often referred to as the “zero rule,” is a heuristic principle rather than a direct rule that Codd outlined. The easiest way to understand Rule Zero is that it states: “A database must be entirely relational.” This principle is so fundamental that it is considered implicit in the definition of a relational database.

Rule Zero: The Holistic Concept of Relational Integrity

Rule Zero serves as a non-negotiable foundation from which the other rules derive their meaning and significance. Just as a building needs a solid foundation to stand, a relational database needs to satisfy Rule Zero to be considered truly relational. Unlike the other rules, which are prescriptive and detailed, Rule Zero acts as a guiding principle that ensures the system adheres to the relational paradigm in its entirety. It encapsulates the essence of Codd's relational theory and provides a lens through which the other rules can be understood and evaluated.

Why 12 Rules Instead of 13?

The regular citation of twelve rules instead of the original thirteen can be attributed to a few factors:

Rule Zero, while important, is often considered a guiding principle rather than a distinct rule. It is seen as a conceptual underpinning that aligns with the core principles of relational theory. Simplification for instructional and training purposes. The twelve rules are typically easier to remember and apply in practice, making them more accessible to database developers and students. The evolution of database technology. Since the original thirteen rules were proposed, the field has advanced, and the need for additional rules or clarifications has emerged. Therefore, the twelve rules summary can be seen as a more current and concise representation of the foundational principles.

Concluding Thoughts

While E.F. Codd’s original proposal of thirteen rules provides a comprehensive and detailed framework for evaluating relational database management systems, the simplified representation of twelve rules, often supplemented by Rule Zero, has served a valuable purpose. Rule Zero, a heuristic principle, has become a cornerstone in the understanding and application of Codd’s relational theory. The number 12 has become the standard due to its practicality, simplicity, and the ability to encapsulate the essential principles effectively.

Understanding these rules is crucial for anyone involved in database management, whether as a developer, designer, or administrator. By adhering to these principles, one can ensure that the database remains relational in its design and operation, thereby providing robust, efficient, and scalable data management solutions.