Code rule of dbms to rdbms?

Codd's twelve rules are a set of thirteen rules (numbered zero to twelve) proposed by Edgar F. Codd, a pioneer of the relational model fordatabases, designed to define what is required from a database management system in order for it to be considered relational, i.e., a relational database management system (RDBMS).[1][2] They are sometimes jokingly referred to as "Codd's Twelve Commandments".

The relational DBMS model is based on the relational algebra devised by E.F.CODD.

The relational algebra by Codd is done through 12 rules popularly known as CODD's 12 Rules.

(1)Information Rule:

All information in a relational database including table names column names are

represented explicitly by values in tables.Knowledge of only one language is necessary to

access all data such as description of the table and attribute definitions integrity

constraints action to be taken when constraints are voilated and security information.

(2)Guaranted Access Rule:

Every pieceof data in the relational database can be accessed by using a

combination of a table name a primary key value that identifies the row and a column

that identifies the cell.The benefit of this is that user productivity is improved

since there is no need to resort to using physical pointers addresses.Provides

data independence.

(3)Systematic treatment of Nulls Rule:

The RDBMS handles that have unknown on inapplicable values in a predefined fashion.

RDBMS distinguishes between zeros blanks and nulls in records and handles such values in

a consistent manner that produces correct answers comparisions and calculations.

(4)Active On-Line Catalog Based on the Relational Model.

THe description of a database and its contents are database tables and therefore

can be queries online via the data language.The DBA's productivity is improved since

changes and additionsto the catalog can be done with the same commands that are

used to access any other table.All queries and reports can be done as with other tables.

(5)Comprehensive Data Sublanguage Rule:

A RDBMS may support several languages but atleast one of them allows the user to do all

of the following:define tables view query and update data set integrity constraints

set authorization and define transactions.

(6)View Updating Rule:

Any view that is theoretically updatable if changes can be made to the tables that

effect the desired changes in the view.Data consistency is ensured since changes

in the underlying tables are transmittedto the view they support.Logical data

independence reduces maintenance cost.

(7)High Level Inserts Update and Delete:

THe RDBMS supports insertion updation and deletion at a table level.With this the

RDBMS can improveperformance by optimizing the path to be taken to execute the action

Ease of use improved since commands act on set of records.

(8)Physical data Independence :

The execution of adhoc requests and application programs is not affected by changes

in the physical data access and storage methods.Database administrators can make

the changes to physical acccess and storage methods which improve performance

but do not changes in the application programs or adhoc requests.This reduces

maintenance costs.

(9)Logical data Independence:

Logical changes in tables and view such asadding/deleting columns or changing

field lenghts do not necessitate modifications in application programs or in the

format of adhoc requests.

(10)Integrity Independance:

Like table/view definitions integrity constraints are atored in the

on-line catalog and therefore can be changed without necessitating changes

in application programs or in the format of adhoc requests .

The following two integrity constraints must be supported.

(a)Entity Integrity:

No component of primary key is allowed to have anull value.

(b)Referential integrity:

For each distinct non-null foreign key value in a relationaldatabase

there must exist a matching primary key from the same range of data value.

(11)Distribution Independence:

Application programs and adhoc requests are not affected by changes

in the distribution of the physical data.

(12)Nonsubversion Rule:

If the RDBMS has a language change that accesses the information

of a record at a time this language cannot be used to by-pass the

integrity constraints.Inoreder to adhere to this rule the RDBMS must have an

active catalog that containsthe constraints must have a logical data independence.