Oracle Codd's 12 Rules

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 Authorization 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).