The year is 2025 and only now I learned about Edgard F. Codd’s 12 rules for database systems to be considered relational. For the records, I had my first contact with relational databases back in 1994.
the rules
Rule 0, The foundation rule: For any system that is advertised as, or claimed to be, a relational data base management system, that system must be able to manage data bases entirely through its relational capabilities.
Rule 1, The information rule: All information in a relational data base is represented explicitly at the logical level and in exactly one way – by values in tables.
Rule 2, The guaranteed access rule: Each and every datum (atomic value) in a relational data base is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.
Rule 3, Systematic treatment of null values: Null values are supported in fully relational DBMS for representing missing information and inapplicable information in a systematic way, independent of data type.
Rule 4, Dynamic online catalog based on the relational model: The database description is shown in a way that’s easy to understand, just like regular data. This makes it simple for authorized users to query it using the same language they use for other data.
Rule 5, The comprehensive data sublanguage rule: A relational system may support several languages and various modes of end use. However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and that is comprehensive in supporting all of the following items:
- Data definition.
- View definition.
- Data manipulation.
- Integrity constraints.
- Authorization.
- Transaction boundaries (begin, commit and rollback).
Rule 6, The view updating rule: All views that are theoretically updatable are also updatable by the system.
Rule 7, Relational Operations Rule / Possible for 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, update and deletion of data.
Rule 8, Physical data independence: Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representations or access methods.
Rule 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.
Rule 10, Integrity independence: Integrity constraints specific to a particular relational data base must be definable in the relational data sublanguage and storable in the catalog, not in the application programs.
Rule 11, Distribution independence: The end-user must not be able to see that the data is distributed over various locations. Users should always get the impression that the data is located at one site only.
Rule 12, The nonsubversion rule: If a relational system has a low-level (single-record-at-a-time) language, that low level cannot be used to subvert or bypass the integrity rules and constraints expressed in the higher level relational language (multiple-records-at-a-time).
more on the rules
“Codd’s 12 Rules”. RelDB.org. 2019-06-30. Retrieved August 14, 2020.