Java Reference
In-Depth Information
Table 1-1: Codd's Rules
Rule
Name
Description
structure.
5
Sub Language Rule
An RDBMS must support a clearly defined
data-manipulation language that comprehensively
supports data manipulation and definition, view
definition, integrity constraints, transactional boundaries,
and authorization.
6
View Update Rule
Data can be presented to the user in different logical
combinations called views. All views must support the
same range of data-manipulation capabilities as are
available for tables.
7
High Level Language
Rule
An RDBMS must be able to retrieve relational data sets.
It has to be capable of inserting, updating, retrieving, and
deleting data as a relational set.
8
Physical Data
Independence Rule
Data must be physically independent of application
programs.
9
Logical Data
Independence Rule
Applications software must be independent of changes
made to the base tables.
10
Integrity Independence
Rule
Integrity constraints must be specified separately from
application programs and stored in the catalog. It must
be possible to change such constraints when
appropriate without unnecessarily affecting existing
applications.
11
Distribution Independence
Rule
Existing applications should continue to operate
successfully when a distributed version of the DBMS is
introduced or when existing distributed data is
redistributed around the system.
12
Non Subversion Rule
If an RDBMS has a low-level (record-at-a-time) interface,
that interface cannot be used to subvert the system or to
bypass a relational security or integrity constraint.
Rather than explaining Codd's Rules in the order in which they are tabulated, it is
much easier to explain the practical implementation of a RDBMS and to refer to the
relevant rules in the course of the explanation. For example, Rule 1, the Information
Rule, requires that a ll data be represented as values in tables; it is important to
understand the idea of tables before moving on to discuss Rule 0, which requires that
the database be managed in accordance with its own rules for managing data.
