Codd's Rule

7/29/2019 Codd's Rule

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Presentation OnCODDs Rules

SUBMITTED TO: SUBMITTED BY:Lec. Rajan Manroo Shallu Puri(76),

Shilpa Mahajan(78)MCA 2nd(B).


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CODDs RULES Dr. E.F. Codd (Edgar Frank Codd), the founder of

the relational database systems framed 13 (0 to 12)rules in June 1970,in ACM (Association of ComputerMachinery) to define how to determine whether aDBMS is relational and to what extent it is relational.

An RDBMS product has to satisfy at least six of the 12rules of Codd to be accepted as a full-fledged RDBMS.


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Rule 0: Foundation

A relational database managementsystem must use only its relational

capabilities to manage theinformation stored in the database.


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Rule 1: Information

All information in the databaseshould be represented in one andonly one way -Namely by values incolumn positions within rows of

tables.

Everything within the databaseexists in tables and is accessedvia table access routines.


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Rule 2: Guaranteed Access

This rule is essentially arestatement of the fundamentalrequirement for primary keys.

Every individual scalar value inthe database must be logicallyaddressable by specifying thename of the containing table,

the name of the containingcolumn and the primary keyvalue of the containing row.


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Rule 3: Comprehensive DataSub-Language (Contd..)

A relational system may support

several languages and variousmodes of terminal use. However,there must be at least onelanguage whose statements are

expressible, having well-definedsyntax and ability to support allof the following iscomprehensible:


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data definition

View definition

data manipulation(interactive and by program)

integrity constraints

Authorization

transaction boundaries(begin, commit and rollback).


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Rule 4: View Updating

A View can represent a subsetof the data contained in a table.Views can limit the degree of

exposure of a table.

All views that are theoreticallyupdatable are also updatable bythe system . Not only can the user

modify data, but so can theRDBMS when the user is notlogged-in.


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Rule 5: High Level Insert,

Update & Delete

This rule states that insert, update,and delete operations should besupported for any retrievable setrather than just for a single row ina single table. This means that datacan be retrieved from a relationaldatabase in sets constructed of datafrom multiple rows and/or

multiple tables. The user should be able to modify

several tables by modifying the viewto which they act as base tables.


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Rule 6: Physical Data

Independence

The ability to change the physicalschema without changing the logical

schema is called physical dataindependence.

For example a change to the internalschema such as using different file

organization or storage structure,storage devices or indexing strategyshould be possible without having tochange the conceptual/external schema.


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Rule 7: Logical Data

Independence The ability to change the logical

schema without changing theexternal schema or application

programs is called as Logical DataIndependence.

For example: the addition or removalof new entities, attributes orrelationship to the conceptual schema

should be possible without having tochange the existing external schemas orhaving to rewrite existing applicationprograms.


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Rule 8: Integrity

Independence The database language must be capable of

defining integrity rules. They must be stored inthe online catalog, not in the application

programs. There are two integrity constraints that must

be supported:

Entity integrity: It states that no primarykey value can be null.

Referential integrity: The referentialintegrity constraint is specified between tworelations and is used to maintain theconsistency among tuples in the two relations.


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Rule 9: Distribution

Independence The RDBMS may spread across

more than one system andacross several networks, howeverto the end-user the tables shouldappear no different to thosethat are local.

It enable application programs

and terminal activities to remainlogically unimpaired whetherand whenever data are physicallycentralized or distributed.


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Rule 10: Non Subversion

If a relational system has a low-level(single-record-at-a-time) language, thatlow level cannot be used to subvert orbypass the integrity Rules and

constraints expressed in the higher levelrelational language (multiple-records-at-a-time) i.e. in SQL server whateverintegrity rules are applied on every recordare also applicable when you process a

group of records using applicationprogram in any other language (e.g. C#,VB.net etc.)


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Rule 11: Systematic Treatement Of

Null Values

If data does not exist or does notapply then a value of NULL is applied,this is understood by the RDBMS as

meaning non-applicable data. The DBMS must have a consistent

method of representing null values.Forexample, for numeric data it must bedistinct from zero or any other

numeric value & for character data itmust be different from a string ofblanks.


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Rule 12:Data Description

The data base description isrepresented at the logical level inthe same way as-ordinary data, sothat authorized users can apply

the same relational language to itsinterrogation as they apply to theregular data .Create, Drop, Alterare the statements that comes indata description/definitionlanguage to modify the schemaof the database by adding,changing, or deletingdefinitions of tables .


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Codd's Rule