e.f codds rules.ppt

8/10/2019 E.F CODDS RULES.ppt

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2Copyright 2007 Accenture All R

Data Models." A data model is a model that descri#es in an

a#stract $ay ho$ data is represented in a #usinessorgani%ation, an information system or a data#asemanagement system.

" &here are #asically ' classic data models(. Hierarchical ata )odel2. *et$or! ata )odel'. Relational ata )odel


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&ype of ata )odel escription

Hierarchical )odel +ell suited for data $hich

are related hierarchically

*et$or! )odel ata#ase model conceivedas fle i#le $ay ofrepresenting o#-ects andtheir relationships

Relational )odel ata is represented in theform of t$o dimensionalta#les


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Features O Relatio!al

Model" &he relational model of data permits the data#ase

designer to create a consistent, logical representationof information.

" &he #asic principle of the relational model is thenformation Principle/ all information is represented #ydata values in relations.

" ata#ase )anagement ystems must adhere toCodd1s rules to #e termed as R ) .


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RDBMS." A relational data#ase management system

3R ) 4 uses matching values in multiple ta#les torelate to the information in one ta#le $ith theinformation in the other ta#le.

" &he t$o most prominent characteristics of arelational data#ase are

(. ata stored in ta#les2. Relationships #et$een ta#les


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7/207Copyright 2007 Accenture All R

Codds Rules.." *o commercial R ) fully conforms to all (2 rules.

" &he rules are so strict that all popular so calledrelational ) s fail on many of the criteria.

" n practice, many data#ase products 3for e . 6racle,

y#ase etc..4 are considered relational1 even if they donot strictly adhere to all (2 rules.



Lets e'i!.." Rule (/ &he nformation Rule /

(. All data should #e presented to the user in ta#leform.

2. All information in the data#ase to #e represented inone and only one $ay, *amely #y values in column

positions $ithin ro$s of ta#les.



Rule (." 8uaranteed Access Rule /

" 9ach piece of data 3atomic data4 must #e logicallyaccessi#le #y referencing

(. A ta#le2. A primary or uni:ue !ey value and

'. A column



Rule )." ystematic &reatment 6f *ull ;alues /

" &he ) must allo$ each field to remain null 3orempty4.

" *ull must al$ays #e interpreted as an un!no$nvalue.



Rule *" ynamic 6nline Catalog #ased on the

relational model /

"


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Rule ,";ie$



Rule -"High=level insert, update and delete /

" The system must support set-at-a-time INSERT,UPDATE, and DELETE operators.



Rule "Physical ata ndependence /

" Applications that access data in a relational data#asemust #e unaffected #y changes in the $ay the data isphysically stored.



Rule /">ogical ata ndependence /

" &he data#ase schema or structure of ta#les 3logical4 ?relationships can change $ithout having to recreatethe application that uses it.

" ifficult to satisfy.


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Rule 00" istri#ution ndependence /

" A relational ) has distri#ution independence.

" &he R ) may spread across more than onesystem ? across several net$or!s, ho$ever to the

end=user the ta#les should appear no different to thosethat are local.



Rule 0("*on u#version Rule /

" *o $ay to modify the data#ase structure other thanthrough the multiple ro$ data#ase language.



&han! @ou

e.f codds rules.ppt

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