Explain the CODD’s Rules for RDBMS?

Relational database theory was first introduced by Edgar Frank Codd in 1970. Edgar Frank Codd was a British computer scientist who, while working for IBM, invented the relational model for database management the theoretical basis for relational databases. Codd defined 13 rules, often termed “Cod’s 12 rules” because he numbered them from zero through 12, on satisfying a relational model, These rules serve as the framework for what a truly relational database should be.

These rules are:

Foundation Rule: A relational database management system must manage its stored data using only its relational capabilities.

Information Rule: All information in the database should be represented in one and only one way as values in a table.

Guaranteed Access Rule: Each and every datum (atomic value) is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.

Systematic Treatment of Null Values: Null values (distinct from empty character string or a string of blank characters and distinct from zero or any other number) are supported in the fully relational DBMS for representing missing information in a systematic way, independent of data type.

Dynamic On-line Catalog Based on the Relational Model: The database description is represented at the logical level in the same way as ordinary data, so authorized users can apply the same relational language to its interrogation as they apply to regular data.

Comprehensive Data Sub-language Rule:  A relational system may support several languages and various modes of  terminal use. However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and whose ability to support all of the following is comprehensible:

  1. Data definition.
  2. View definition.
  3. Data manipulation (interactive and by program).
  4. Integrity constraints.
  5. Authorization.
  6. Transaction boundaries (begin, commit, and rollback).

View Updating Rule: All views that are theoretically update-able are also update-able by the system.

High-level Insert, Update and Delete: The capability of handling a base relation or a derived relation as a single operand applies not only to the retrieval of data but also to the insertion, updation, and deletion of data.

Physical Data Independence: Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representation or access methods.

Logical Data Independence:. Application programs and terminal activities remain logically unimpaired when information preserving changes of any kind that theoretically permit un-impairment are made to the base tables.

Integrity Independence: Integrity constraints specific to a particular relational database must be definable in the relational data sub-language and storable in the catalog, not in the application programs.

Distribution Independence: The data manipulation sub-language of a relational DBMS must enable application programs and terminal activities to remain logically unimpaired whether and whenever data are physically centralized or distributed.

Non-subversion Rule: If a relational system has or supports a low-level (single -record -at -a -time) language, that low-level language cannot be used to subvert or bypass the integrity rules or constraints expressed in the higher -level (multiple -records -at -a -time) relational language.

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