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CODD Rules

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April 2013
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CODD Rules

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Edgar F. Codd, proposed thirteen rules (0 to 12) to define what is require d from a DBMS in order for it to be considered relational. Currently there is no commercial database management system which fully satisfies all the CODD’s rules.

Rule No
Rule Name
0   Foundation rule The system must qualify as relational both as a database and as a management system.
1   The information rule All information in the database should be represented in one and only one way as values in a table.
2   The guaranteed access rule All data must be accessible. This means each data item can be uniquely identified using the table name, primary key, and column name.
3   Systematic treatment of null values Null values are supported in the fully relational DBMS for representing missing information in a systematic way, independent of data type.
4   Active online 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.
5   The 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
6.Transaction boundaries (begin, commit, and rollback)
6   The view updating rule All views that are theoretically updateable are also updateable by the system.
7   High-level insert, update, and delete The capability of handling a base relation or a derived relation as a single operand applies nor only to the retrieval of data but also to the insertion, update and deletion of data.
8   Physical data independence Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representation or access methods.
9   Logical data independence Application programs and terminal activities remain logically unimpaired when information preserving changes of any kind that theoretically permit unimpairment are made to the base tables.
10   Integrity independence Integrity constraints specific to a particular RDBMS must be definable in the relational data sub language and storable in the catalog, not in the application programs.
11   Distribution independence The data manipulation sub language of an RDBMS must enable application programs and terminal activities to remain logically unimpaired whether and whenever data are physically centralized or distributed.
12   The non subversion rule If an RDBMS 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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