|Note: I have presented papers at conferences in Bulgaria, Estonia, and Finland with Chris Date and,
if nothing else, one thing that has become abundantly clear is that if you don't know who Edwin Codd and Chris Date are you should find out
before you read this page. And if you have not read at least two of Edwin Codd's papers, and at least one of Chris Date's books you will not
understand the information on this page not matter how well you may be able to delude yourself otherwise.
|Rule 1: The Information
All information in a relational database is represented explicitly at the logical level and in exactly one way - by values in tables.
|Rule 2: Guaranteed Access
||Each and every datum (atomic value) in a relational database 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 (distinct from the empty character string of blank characters and distinct from any zero
or other numbers) are supported in fully relational DBMS for representing missing information and inapplicable information in a systematic way.
|Rule 4: Dynamic Online Catalog Based on the Relational Model
||The database description is represented at the logical level in the same way as ordinary data, so
that authorized users can apply the same relational language to its interrogation as they apply to the regular data.
|Rule 5: Comprehensive Data Sub-language
||A relational system may support several languages and various modes of terminal use (for example,
the fill-in-the-blanks mode). However, there must be at least one language whose statements are expressible, per some well-defined syntax,
as character strings, that is comprehensive in supporting all of the following items:
- Data Definition
- View Definition
- Data manipulation (interactive and by program)
- Integrity Constraints
- Transaction boundaries (begin, commit, and rollback)
|Rule 6: View Updating
||All views that are theoretically updateable are also updateable by the system.
|Rule 7: 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 database must be definable
in the relational data sub-language and storable in the catalog, not in the application programs.
|Rule 11: Distribution Independence
||A relational DBMS has distribution dependence.
|Rule 12: Nonsubversion
||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).