what are the 12 codd's rule
What are the
twelve codd’s rule
Codd’s rules
are a set of guidelines and principels that define the characteristics that
define the characteristics that relational database management system (RDBMS)
must meet to be considered a truly rlational database. Here are the 12 Codd’s
Rules:
Rule 0: The
Foundation Rule
A relational
DBMS must be able to mange its data entirely trough its relational
capabilities.
Rule 1:
Information rule
All data in
a relational database is to be represented in one and only one way, namely by
values in tables.
Rule 2:
Guaranteed Access Rule
Each and
every data element (atomic value) is guaranteed to be accessible logically with
a combination of table name, primary key value, and column name.
Rule 3:
systematic Treatment of Null values
Null value
are treated uniformly and systematically.
Rule 4:
Dynamic online catalog Based on the Relational model
The database
schema must be stored in the same relational format as regular data.
Rule 5:
Comprehensive data sublanguage Rule
A relational
data base management system must support at least one well defined language
that is capable of providing support for data definition, data manipulation,
and data control operations.
Rule 6: View
Updating Rule
Views(virtual
tables) can be updated just as if they were tables themselves.
Rule 7:
High-level Insert,Update, and Delete Rule
The
capability of handling a set of records, or a tuple, at once, rather than one
at a time.
Rule 8:
Physical Data Independence
The
application program and terminal must remain logically unimpaired Whenever any
changes are made in the storage representation or access methods.
Rule 9:
Logical Data Independence
Modifications
to the logical scheme must not require changes to the application programs that
access the data.
Rule 10:
Integrity Independence
Integrity
constraints must be specified separetly from application programs and stored in
the catalog.
Rule 11:
Distribution Independence
The
distribution of portions of the databse to various locations should be
transparent to users of the system.
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