Codd’s 12 Rules (13 Rules)

Summary

This presentation delves into Codd's 12 Rules for defining the requirements of a Relational Database Management System (RDBMS). The rules, proposed by Edgar Frank Codd, are numbered from 0 to 12, hence the name. They ensure that an RDBMS manages databases through relational capabilities, represents all information explicitly, guarantees access to every datum, systematically treats null values, and maintains physical and logical data independence. The rules also mandate the use of a comprehensive data sublanguage, support for view updating, and uphold integrity constraints. Lastly, they address the importance of distribution independence and non-subversion to ensure the system's integrity.

Takeaways

• 📚 The presentation introduces 'Codd's 12 Rules', a set of 13 foundational principles for a database management system (DBMS) to be considered relational, proposed by Edgar Frank Codd.
• 🔑 Rule 0, the 'Foundation Rule', asserts that a relational DBMS must manage databases entirely through its relational capabilities.
• 📊 Rule 1, the 'Information Rule', states that all information in a relational database should be represented explicitly at the logical level in a single way, through table values.
• 🔍 Rule 2, the 'Guaranteed Access Rule', ensures that every atomic value in the database can be accessed using the table name, primary key, and column name.
• 🚫 Rule 3 addresses the 'Systematic Treatment of Null Values', emphasizing that nulls represent missing or inapplicable information and must be treated consistently across data types.
• 📖 Rule 4, the 'Dynamic Online Catalog', requires that the database description and user authorization details are logically represented and accessible.
• 💬 Rule 5, the 'Comprehensive Data Sublanguage Rule', mandates that at least one language for the DBMS must support data definition, view definition, and transaction operations.
• 🔄 Rule 6, the 'View Updating Rule', ensures that updates to views are reflected in the underlying tables, maintaining data consistency.
• 🔧 Rule 7, the 'Relational View of Data Access', allows for high-level operations such as insert, update, and delete to be performed not just at the database level but also through application programs.
• 🏭 Rule 8, 'Physical Data Independence', ensures that application programs remain unaffected by changes in the physical storage or access methods of the database.
• 🌐 Rule 9, 'Logical Data Independence', guarantees that changes to the database schema do not impact the application logic, maintaining logical separation.
• 🔒 Rule 10, 'Integrity Independence', stipulates that integrity constraints should be definable and stored in the DBMS, not in application programs.
• 🌐 Rule 11, 'Distribution Independence', highlights the importance of data distribution across different locations for redundancy and disaster recovery, without user awareness of the distribution.
• 🛡️ Rule 12, the 'Non-Subversion Rule', asserts that a low-level language, if present, must not be used to bypass the integrity constraints defined in the higher-level relational language.

Q & A

What are Codd's 12 Rules for a database management system to be considered relational?

Codd's 12 Rules, also known as the 12 Commandments, are a set of 13 rules that define the requirements for a database management system (DBMS) to be considered a relational database management system (RDBMS). These rules were proposed by Edgar Frank Codd, the pioneer of the relational model for databases.

Why are there 13 rules in Codd's 12 Rules?

There are 13 rules in Codd's 12 Rules because the rules are numbered from 0 to 12, with the first rule being rule number zero and the last rule being rule number 12.

What is the significance of Rule Number Zero in Codd's 12 Rules?

Rule Number Zero, the foundation rule, states that a system claiming to be an RDBMS must be able to manage databases entirely through its relational capabilities, closely associating with the mathematical concept of relations.

What does the Information Rule (Rule Number One) imply for a relational database?

The Information Rule implies that all information in a relational database is represented explicitly at the logical level and in exactly one way, which is by values in the table.

Can you explain the Guaranteed Access Rule (Rule Number Two)?

The Guaranteed Access Rule states that each atomic value in a relational database must be logically accessible using a combination of table name, primary key, and column name.

How does Rule Number Three address null values in a relational database?

Rule Number Three, the Systematic Treatment of Null Values, states that null values, representing missing or inapplicable information, must be treated systematically by the RDBMS and must be independent of the data type.

What is the purpose of the Dynamic Online Catalog (Rule Number Four)?

The Dynamic Online Catalog ensures that the database description is represented at the logical level and deals with authorization, determining what data users can access.

What capabilities must a relational system support according to the Comprehensive Data Sublanguage Rule (Rule Number Five)?

The Comprehensive Data Sublanguage Rule requires that there must be at least one language supported by the system that can express data definition, view definition, data manipulation, integrity constraints, authorization, and transaction operations.

What does the View Updating Rule (Rule Number Six) require for a relational database?

The View Updating Rule mandates that any updates made to a view in an RDBMS should also update the underlying table or relation, as they both refer to the same data item in memory.

What is the importance of the Physical Data Independence (Rule Number Eight)?

Physical Data Independence ensures that application programs and terminal activities remain logically unimpaired when changes are made to the storage representations or access methods at the database level.

How does the Integrity Independence (Rule Number Ten) differ from Integrity constraints in application programs?

Integrity Independence requires that all integrity constraints specific to a relational database must be definable and stored in the relational data sublanguage, not in the application programs, ensuring that the constraints are managed at the DBMS level.

What does the Non-Subversion Rule (Rule Number Twelve) prevent in a relational system?

The Non-Subversion Rule ensures that if a relational system has a low-level language for single-record operations, it cannot be used to subvert or bypass the integrity rules and constraints expressed in the higher-level relational language.