The rules
Rule 0: The system must qualify as relational, as a database, and as a management
system.
For a system to qualify as a relational database management system (RDBMS),
that system must use its relational facilities (exclusively) to manage the database.
Rule 1: The information rule:
All information in the database is to be represented in one and only one way,
namely by values in column positions within rows of tables.
Rule 2: The guaranteed access rule:
All data must be accessible. This rule is essentially a restatement of the
fundamental requirement for primary keys. It says that every individual scalar
value in the database must be logically addressable by specifying the name of the
containing table, the name of the containing column and the primary key value of
the containing row.
Rule 3: Systematic treatment of null values:
The DBMS must allow each field to remain null (or empty). Specifically, it must
support a representation of "missing information and inapplicable information"
that is systematic, distinct from all regular values (for example, "distinct from
zero or any other number", in the case of numeric values), and independent of
data type. It is also implied that such representations must be manipulated by the
DBMS in a systematic way.
Rule 4: Active online catalog based on the relational model:
The system must support an online, inline, relational catalog that is accessible to
authorized users by means of their regular query language. That is, users must be
able to access the database's structure (catalog) using the same query language
that they use to access the database's data.
Rule 5: The comprehensive data sublanguage rule:
The system must support at least one relational language that
1. Has a linear syntax
2. Can be used both interactively and within application programs,
3. Supports data definition operations (including view definitions),
data manipulation operations (update as well as retrieval), security and
integrity constraints, and transaction management operations (begin,
commit, and rollback).
Rule 6: The view updating rule:
All views that are theoretically updatable must be updatable by the system.
Rule 7: High-level insert, update, and delete:
The system must support set-at-a-time insert, update, and delete operators. This
means that data can be retrieved from a relational database in sets constructed of
data from multiple rows and/or multiple tables. This rule states that insert, update,
and delete operations should be supported for any retrievable set rather than just
for a single row in a single table.
Rule 8: Physical data independence:
Changes to the physical level (how the data is stored, whether in arrays or linked
lists etc.) must not require a change to an application based on the structure.
Rule 9: Logical data independence:
Changes to the logical level (tables, columns, rows, and so on) must not require a
change to an application based on the structure. Logical data independence is
more difficult to achieve than physical data independence.
Rule 10: Integrity independence:
Integrity constraints must be specified separately from application programs and
stored in the catalog. It must be possible to change such constraints as and when
appropriate without unnecessarily affecting existing applications.
Rule 11: Distribution independence:
The distribution of portions of the database to various locations should be
invisible to users of the database. Existing applications should continue to operate
successfully:
1. when a distributed version of the DBMS is first introduced; and
2. When existing distributed data are redistributed around the system.
Rule 12: The nonsubversion rule:
If the system provides a low-level (record-at-a-time) interface, then that interface
cannot be used to subvert the system, for example, bypassing a relational security
or integrity constraint.
