Скачать или смотреть Relational Model: codd's Rules

Dive deep into the foundational principles of relational databases!

This video explores Codd's 12 Rules, a set of guidelines that define the characteristics of a true relational database management system (RDBMS). We'll break down each rule, explaining its significance and how it contributes to data integrity, independence, and overall database efficiency.

Key topics covered:

What is a Relational Database?
Codd's 12 Rules Explained Simply
Importance of Codd's Rules in Modern Databases
Real-world Examples and Applications
Whether you're a beginner or looking to refresh your database knowledge, this video provides a clear and concise understanding of Codd's Rules and their enduring impact.


Dr. Edgar F. Codd, the father of the relational database model, proposed 12 rules (actually 13, including rule 0) to define what constitutes a relational database system. These rules serve as a guideline for database management systems (DBMS) to ensure consistency, reliability, and efficiency. Let’s break them down:

Rule 0: Foundation Rule
A system must qualify as a relational database system if it supports relational management of databases.
It implies that all other rules must be followed to be considered a relational database.
Rule 1: Information Rule
All data must be represented as values in tables.
Each value in a cell must be atomic (indivisible).
Rule 2: Guaranteed Access Rule
Each piece of data should be accessible using a combination of a table name, primary key, and column name.
Example: To find a student’s name, you need the table name (Students), column name (Name), and the primary key (StudentID).
Rule 3: Systematic Treatment of NULL Values
NULL values must be uniformly supported to represent missing, unknown, or inapplicable information.
NULL should not confuse operations or result in errors.
Rule 4: Dynamic Online Catalog
The database’s structure (metadata) must be stored in the database itself and accessible via the same language used to manage data (e.g., SQL).
Rule 5: Comprehensive Data Sublanguage Rule
A relational system must support a comprehensive language for defining, manipulating, and querying data.
Example: SQL provides SELECT, INSERT, DELETE, and other commands for all operations.
Rule 6: View Updating Rule
All views (virtual tables) must be updatable if the underlying base table is updatable.
Example: You should be able to update a view of employee salaries if it reflects a base table.
Rule 7: High-Level Insert, Update, and Delete
A relational system must support set-level operations.
Example: Insert, update, or delete multiple rows in a single command.
Rule 8: Physical Data Independence
Changes in the physical storage of data should not affect how users interact with the data.
Example: If data storage moves from HDD to SSD, user queries should remain unaffected.
Rule 9: Logical Data Independence
Changes in the logical structure (schema) of the database should not affect user interactions.
Example: Adding a column to a table should not break existing queries.
Rule 10: Integrity Independence
Integrity constraints (like primary key, foreign key, and domain constraints) must be defined in the database itself, not in application programs.
Rule 11: Distribution Independence
A relational system should work seamlessly whether the data is stored on a single system or distributed across multiple locations.
Rule 12: Non-Subversion Rule
If a system provides a lower-level access method, it must not bypass integrity rules or security constraints.

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