What are 12 rules of Dr. Edgar Frank “Ted” Codd?
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| Dr. Edgar Frank “Ted” Codd (E. F. Codd) |
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Microsoft SQL Server for beginner’s tutorial is divided into many parts
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database, Create, Alter, Delete and Drop database objects like Database,
Tables, Views, Indexes, Triggers, UDFs (User Defined Functions), Synonyms, SPs
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Today I will
discuss about 12 rules of a RDBMS (Relational Data Base Management Systems)
which has been taken from a link is mentioned below -
Let’s start
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Dr. E.F. Codd's 12 Rules: Dr Edgar F. Codd did some extensive research in Relational Model of
database systems and came up with twelve rules of his own which according to
him, a database must obey in order to be a true relational database.
These rules can be applied on a database system that is capable of
managing is stored data using only its relational Capabilities. This is a
foundation rule, which provides a base to imply other rules on it.
Rule 1: Information rule: This rule states
that all information (data), which is stored in the database, must be a value
of some table cell. Everything in a database must be stored in table formats.
This information can be user data or meta-data.
Rule 2: Guaranteed Access rule: This rule
states that every single data element (value) is guaranteed to be accessible
logically with combination of table-name, primary-key (row value) and
attribute-name (column value). No other means, such as pointers, can be used to
access data.
Rule 3: Systematic Treatment of NULL values: This rule states the NULL values in the database must be given a
systematic treatment. As a NULL may have several meanings, i.e. NULL can be
interpreted as one the following: data is missing, data is not known, data is
not applicable etc.
Rule 4: Active online catalog: This rule states
that the structure description of whole database must be stored in an online
catalog, i.e. data dictionary, which can be accessed by the authorized users.
Users can use the same query language to access the catalog which they use to
access the database itself.
Rule 5: Comprehensive data sub-language rule: This rule states that a database must have a support for a language
which has linear syntax which is capable of data definition, data manipulation
and transaction management operations. Database can be accessed by means of
this language only, either directly or by means of some application. If the
database can be accessed or manipulated in some way without any help of this
language, it is then a violation.
Rule 6: View updating rule: This rule states
that all views of database, which can theoretically be updated, must also be
updatable by the system.
Rule 7: High-level insert, update and delete rule: This rule states the database must employ support high-level
insertion, Updation and deletion. This must not be limited to a single row that
is, it must also support union, intersection and minus operations to yield sets
of data records.
Rule 8: Physical data independence: This rule
states that the application should not have any concern about how the data is
physically stored. Also, any change in its physical structure must not have any
impact on application.
Rule 9: Logical data independence: This rule
states that the logical data must be independent of its user’s view
(application). Any change in logical data must not imply any change in the
application using it. For example, if two tables are merged or one is split
into two different tables, there should be no impact the change on user
application. This is one of the most difficult rule to apply.
Rule 10: Integrity independence: This rule
states that the database must be independent of the application using it. All
its integrity constraints can be independently modified without the need of any
change in the application. This rule makes database independent of the
front-end application and its interface.
Rule 11: Distribution independence: This rule
states that the end user must not be able to see that the data is distributed
over various locations. User must also see that data is located at one site
only. This rule has been proven as a foundation of distributed database
systems.
Rule 12: Non-subversion rule: This rule states that if a system has an
interface that provides access to low level records, this interface then must
not be able to subvert the system and bypass security and integrity
constraints.
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