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Codd’s Rules in DBMS

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In this article at OpenGenus.org, we learn about Codd's Rules in Database Management Systems (DBMS).


  1. Introduction
  2. Key Takeaways
  3. 12 Codd's Rules in DBMS and their usecases.
  4. Conclusion


In the ever-evolving landscape of database management systems (DBMS), the principles laid out by E.F. Codd in his groundbreaking 1970 paper, "A Relational Model of Data for Large Shared Data Banks," continue to serve as the bedrock for relational databases. Codd's Rules, a set of guidelines proposed by Edgar F. Codd, articulate the fundamental requirements for a database to be classified as truly relational. In this exploration, we will dissect the core tenets of Codd's Rules, shedding light on their significance within the realm of DBMS.

Key Takeaways

  1. Codd's Rules provide fundamental guidelines for the design and implementation of relational database management systems.
  2. The rules address aspects such as data integrity, accessibility, and independence, contributing to the efficiency and reliability of databases.
  3. Real-life applications illustrate how these rules are essential for organizing and managing data in diverse domains.
  4. Adhering to Codd's Rules ensures that databases evolve seamlessly, supporting changes in structure and distribution without compromising functionality.
  5. The principles outlined by E.F. Codd remain relevant, influencing the ongoing development and maintenance of modern database systems.

Codd's 12 Rules:

  1. Information Rule:

    Central to Codd's vision is the Information Rule, stipulating that all data in a relational database should reside in one exclusive location – the relational table. This principle minimizes redundancy, ensuring data consistency, manageability, and reliability.

    Use Case:

    In a hospital management system, patient records are stored in a central "Patients" table. Each patient is identified by a unique patient ID (primary key), and details such as name, address, and contact information are stored in the table. This ensures that patient information is centralized, preventing redundancy and maintaining data consistency.

  2. Guaranteed Access Rule:

    A cornerstone of efficient data retrieval, the Guaranteed Access Rule dictates that each data value in a relational database must be accessible through a combination of table name, primary key value, and column name. This ensures a unique identifier for every data element.

    Use Case:

    In a library database, the "Books" table contains information about each book, including a unique ISBN (primary key). Users can efficiently access information about a specific book by querying the table with the ISBN, ensuring guaranteed access to individual book records.

  3. Systematic Treatment of Null Values:

    Codd advocates for a systematic approach in handling null values, distinguishing between the absence of information and a deliberate null value, fostering clarity and precision in database management.

    Use Case:

    In a customer database for an online store, the "Orders" table may include a column for the shipping address. If a customer hasn't provided a shipping address during checkout, the corresponding field is treated as null, distinguishing between cases where the information is absent and cases where it is intentionally left blank.

  4. Dynamic Online Catalog Based on the Relational Model:

    To enhance flexibility and maintainability, Codd's Rules advocate storing the database schema, including metadata and data definitions, in a tabular form, making it as accessible and manipulable as regular data.

    Use Case:

    In a music streaming service, the database schema includes a "Songs" table and a "Genres" table. The dynamic catalog is achieved by storing metadata about song genres in a tabular form. Adding or modifying genres can be done through standard SQL operations, providing flexibility and maintainability.

  5. Comprehensive Data Sublanguage Rule:

    An essential requirement is the support for a comprehensive data sublanguage that allows users to define, manipulate, and query data within the database. SQL, a widely adopted language, exemplifies compliance with this rule.

    Use Case:

    A customer relationship management (CRM) application interacts with a relational database using SQL commands to retrieve customer information, update contact details, and perform other data operations. SQL serves as the comprehensive data sublanguage for seamless communication with the database.

  6. View Updating Rule:

    Codd's vision includes the assurance that views in a relational database, theoretically updatable, should also be updatable by the system. This ensures consistency between modifications made through views and the underlying tables.

    Use Case:

    In a project management database, a view may be created to display tasks pending completion. The View Updating Rule ensures that if a task is marked as complete through the view, the underlying "Tasks" table is updated accordingly.

  7. High-Level Insert, Update, and Delete:

    To simplify user interactions, Codd's Rules advocate for the support of high-level operations for inserting, updating, and deleting data, minimizing the need for users to delve into low-level coding.

    Use Case:

    An inventory management system allows users to add, update, and remove products from the inventory through a user-friendly interface. High-level operations are translated into SQL commands behind the scenes, simplifying user interactions.

  8. Physical Data Independence:

    Changes in the physical storage and organization of data should not disrupt application programs or alter the user's perception of the data. This rule ensures adaptability and ease of maintenance.

    Use Case:

    A social media platform, originally hosted on a local server, migrates its database to a cloud-based infrastructure. The DBMS, adhering to physical data independence, ensures that the change in storage architecture doesn't impact the application's functionality or user experience.

  9. Logical Data Independence:

    Modifications to the logical structure of the database, such as changes to table structures or domains, should not impact application programs, fostering a seamless evolution of the database schema without disrupting existing applications.

    Use Case:

    In an educational institution's database, if the structure of the "Courses" table is modified to include additional information about prerequisites, logical data independence ensures that existing applications handling course information are not disrupted. The changes to the table structure do not affect application programs.

  10. Integrity Independence:

    The specification of integrity constraints, such as primary keys and foreign keys, should be separate from application programs. This separation ensures consistency and simplifies the enforcement of data integrity.

    Use Case:

    In a banking database, the enforcement of a unique customer identification number as a primary key is independent of application programs. Whether a new account is opened through a mobile app or a web portal, the integrity constraint of a unique customer ID is consistently enforced.

  11. Distribution Independence:

    In a networked environment, the distribution of data across various nodes should not affect application programs. This rule is particularly pertinent for databases distributed across multiple locations.

    Use Case:

    In a multinational corporation's database, where employee records are distributed across regional servers, the distribution of data does not affect the application programs. Employees can access their information seamlessly, regardless of the server hosting their data.

  12. The Nonsubversion Rule:

    Codd's final rule underscores the importance of preventing users from bypassing established integrity rules through unauthorized means, reinforcing the significance of maintaining the integrity of the database.

    Use Case:

    In a legal case management system, access controls and encryption are implemented to ensure that users cannot bypass the established security measures through unauthorized means. This safeguards the integrity and confidentiality of sensitive legal information.


Codd's Rules have stood the test of time as a guiding framework for the development of relational database management systems. They embody principles that prioritize data integrity, flexibility, and independence, both logically and physically. Adhering to these rules has become a benchmark for assessing the relational nature of DBMS, ensuring that they align with the high standards set by E.F. Codd over fifty years ago. As the field of database management continues to evolve, Codd's Rules persist as a foundational guide, shaping the design and functionality of robust and efficient relational databases.

With this article at OpenGenus.org, you must have a strong idea of Codd's Rules in DBMS.

Codd’s Rules in DBMS
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