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what is codd's rule?

Asked by: Interview Candidate | Asked on: Aug 24th, 2005
Showing Answers 1 - 15 of 15 Answers
Siva

Answered On : Jul 18th, 2005

In 1985, Edgar Codd published a set of 13 rules which he defined as an evaluation scheme for a product which claimed to be a Relational DBMS.  
 

  
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nitin mishra

Answered On : Aug 24th, 2005

good excellent

  
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rajesh

Answered On : Sep 14th, 2005

codd's rule states that

"any system which claims to be a relation database management system must be able to manage databases entirely through its relational capabilities "

  
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rahul

Answered On : Oct 14th, 2005

Very nice work Anju, I hava one ques., Sive wrote that there are 13 rules and you have put down only 12. Please add the 13th rule if applicable.

  
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PavanKumar.D.V.

Answered On : Oct 29th, 2005

Rule 1: The Information Rule All data should be presented to the user in table form. Last week's newsletter already discussed the basics of this rule. Rule 2: Guaranteed Access Rule All data should be accessible without ambiguity. This can be accomplished through a combination of the table name, primary key, and column name. Rule 3: Systematic Treatment of Null Values A field should be allowed to remain empty. This involves the support of a null value, which is distinct from an empty string or a number with a value of zero. Of course, this can't apply to primary keys. In addition, most database implementations support the concept of a nun- null field constraint that prevents null values in a specific table column. Rule 4: Dynamic On-Line Catalog Based on the Relational Model A relational database must provide access to its structure through the same tools that are used to access the data. This is usually accomplished by storing the structure definition within special system tables. Rule 5: Comprehensive Data Sublanguage Rule The database must support at least one clearly defined language that includes functionality for data definition, data manipulation, data integrity, and database transaction control. All commercial relational databases use forms of the standard SQL (Structured Query Language) as their supported comprehensive language. Rule 6: View Updating Rule Data can be presented to the user in different logical combinations, called views. Each view should support the same full range of data manipulation that direct-access to a table has available. In practice, providing update and delete access to logical views is difficult and is not fully supported by any current database. Rule 7: High-level Insert, Update, and Delete 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 The user is isolated from the physical method of storing and retrieving information from the database. Changes can be made to the underlying architecture ( hardware, disk storage methods ) without affecting how the user accesses it. Rule 9: Logical Data Independence How a user views data should not change when the logical structure (tables structure) of the database changes. This rule is particularly difficult to satisfy. Most databases rely on strong ties between the user view of the data and the actual structure of the underlying tables. Rule 10: Integrity Independence The database language (like SQL) should support constraints on user input that maintain database integrity. This rule is not fully implemented by most major vendors. At a minimum, all databases do preserve two constraints through SQL. No component of a primary key can have a null value. (see rule 3) If a foreign key is defined in one table, any value in it must exist as a primary key in another table. Rule 11: Distribution Independence A user should be totally unaware of whether or not the database is distributed (whether parts of the database exist in multiple locations). A variety of reasons make this rule difficult to implement; I will spend time addressing these reasons when we discuss distributed databases. Rule 12: Nonsubversion Rule There should be no way to modify the database structure other than through the multiple row database language (like SQL). Most databases today support administrative tools that allow some direct manipulation of the datastructure.

  
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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.

  
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maris

Answered On : Mar 7th, 2006

Hai guys and gals

   who knows the clear answer that peron only answer the question ok, pls don't give falls answer's clearly and truly ok

this my simple request

  
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Sri

Answered On : Mar 16th, 2006

Impressive.

  
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balaji

Answered On : Aug 11th, 2006

is it in 1985 or 1970 confirm b'coz i read in a book as 1970

  
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saida dhanavath

Answered On : Aug 13th, 2006

Dr.Edgar.F Codd rules are excellent for claiming a database as RDBMS.

one of the friend given that there are 13 rules. i know only 12 can you plz provide 13th rule given by codd.

thank you for geek's service

  
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Nagi reddy

Answered On : Aug 28th, 2006

There are 13 rules, starts from 0 to 12;

--nagi

  
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madhu sudhan reddy

Answered On : Sep 27th, 2006

It is 1970. It is confirmed because in DATES edition, it is mentioned as 1970.

Codd is a Mathematician.

  
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pv_amburle

Answered On : Nov 4th, 2006

View all answers by pv_amburle

There are 12 code's rules.Every RDBMS has to satisfy atleast 8/9 rules.Oracle is satisfing almost all the rules ( I think it satisfies 11 and half rules).e.g. Null constraints, Data Independancy, Integrity,Redaduncy,..,.... etc..Thanks & RegardsP.A.

  
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rajakumar_na

Answered On : Nov 14th, 2007

View all answers by rajakumar_na

Dr. E.F. Codd, an IBM researcher, first developed the relational data model in 1970. In 1985, Dr. Codd published a list of 12 rules that concisely define an ideal relational database, which have provided a guideline for the design of all relational database systems ever since.

Hey guys,
E.F.Codd published only 12 rules in 1985 for RDBMS. if u have any doubt plz visit this site:
http://www.itworld.com/nl/db_mgr/05072001/

  
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nishant s mevawala

Answered On : Aug 30th, 2011

1.Information Rule
2.Guaranteed Access Rule
3.Systematic Treatment of Nulls Rule
4.Active On-line catalog based on the relational model
5.Comprehensive Data Sub-language Rule

  
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