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DATA MODELS:-

A model is an abstraction process .

A data model also called database modelis a mechanism that provides this abstractionfor database application.

It represents the organisation itself.

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A data model is a collection of mathematically

well-dened concepts that help an enterpriseto consider and express the static anddynamic properties of data intensiveapplications.

It consists of the following

1) Static properties for ex; obects!attrib"tes! relationships.

#) $ynamic properties for ex; operations or

r"les dening new database states.

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$ata %odels can be broadly classied into thefollowing three categories&

1) 'ecord based data models.

#) (bect-based data models.

) *hysical data models.

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Record Based Data Models:-

+hey are "sed to specify the overall

logical str"ct"res of the database.

In this model the database consists of an"mber of xed-format records possibly of

di,erent types.

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+here are three record based data models

1) ierarchical data model

#) etwor/ data model

) 'elational data model

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Object Based Data Models:-

+hey are "sed to describe data and itsrelationships.

It "ses concepts s"ch as entities! attrib"tesand relationships.

It has 0exible data str"ct"ring capabilities.

$ata integrity constraints can be explicitlyspecied.

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+he following are the common types of(bect-based data models&-

1) ntity-'elationship model.

#) Semantic %odel.

) 2"nctional model.

3) (bect-oriented model.

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Physical Data Models:-

+hey are "sed for a higher-leveldescription of storage str"ct"re and access

mechanism.

+hey describe how data is stored in thecomp"ter.

It is possible to implement the database atsystem level "sing physical data models.

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+he most common physical models are&-

1) 4nifying model.

#) 2rame memory model.

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ierarchical $ata %odels&-

+he model is represented by an "pside-down tree.

+he following g"re shows the model

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A

5 6

$

7evel89 & 'oot *arent

:node)

7evel81& 'oot 6hildren

:Segments)

7evel8#& Segments:level-1 children)

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A tree may be dened as a set of nodes s"ch

that there is one designated node called theroot :node)! which is called as the parentnode.

+he remaining nodes are partitioned intodisoint sets and are perceived as children ofthe parent.

+he parent can have none! one or morechildren.

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A hierarchical model can represent one-to-many relationship between two entitieswhere the two are respectively parent andchild.

+he nodes of the tree represents recordtypes.

+he traversal of the tree is done inpreorder! inorder! postorder.

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+he following g"re shows a hierarchicaldata model of a 4I'SI+< tree typeconsisting of three levels and three recordtypes s"ch as $*A'+%+! 2A647+< A$

6(4'S.

+he tree contains information abo"t"niversity academic departments alongwith data on all fac"lties for eachdepartment and all co"rses ta"ght by eachfac"lty within a department.

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4I'SI+ design is simple

i.e.! between vario"s layers .

#) $ata Sharing&-All data held in a common database

sharing is practical.

) $ata Sec"rity&-*rovided and enforced by $5%S.

rst model to provide sec"rity.

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3) $ata Independence&-

$5%S creates an environment inwhich data independence can bemaintained.

S"bstantially decreases theprogramming e,ort and programmaintenance.

@) $ata Integrity&-given a parentchild relationship ! italways promotes data integrity.

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B) Cciency&- It is very eCcient when the database

contains a large vol"me of data inone-to-many :1&m) relationships.Dhen the "sers reE"ire large n"mbers

of transactions "sing data whose

relationships are xed over time.

F) Available expertise&-xperience programmers are

available.

G) +ried 5"siness applications&-tried-and-tr"e b"siness applications

available within the mainframes.

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$isadvantages of ierarchical $ata %odel&-

1) Implementation 6omplexity#) In0exibility

) $atabase management problems3) lac/ of Str"ct"ral Independence@) Application programming 6omplexityB) Implementation limitation

F) o standardsG) xtensive programming e,orts.

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NET%OR& DATA MODEL:-

+he $atabase +as/ Hro"p of the6onference on $ata System 7ang"ages:$5+H6($AS

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It has a ownermember relationship.

%& or 1&%

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A

5 6

$ 2

77-9 &

(D'

77-1 &(D'%%5

'

77-#&%%5'

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SA7S-'*'S+A

+I

64S+(%'

*'($46+I(I6 *A

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Advantages of etwor/ $ata %odel&-

1) Simplicity&simple and easy to design

#) 2acilitating more relationships types&in handling one-to-one and many-to-

many relationships! which helps inmodeling real life sit"ations.

) S"perior data access&3) $atabase Integrity&@) $ata independence&B) $atabase Standards&

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$isadvantages of etwor/ $ata %odel&-

1) System complexity&

#) Absence of str"ct"ral independence&

) ot-a-"ser-friendly&

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RELATIONAL DATA MODEL:-

.2.6odd of I5% research rst introd"cedthe relational data model in 1JF9.

+he relational data model is

implemented "sing very sophisticated'elational $atabase %anagement System:'$5%S).

It performs the same basic f"nctions ofthe hierarchical and networ/ $5%Ss pl"swith the other f"nctions that ma/e'elational $ata model easy to "nderstand

and implement.

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Ad'a(ta)es o* Relatio(al Data Model:-

1) Simplicity

#) Str"ct"ral Independence

) ase of design! implementation!maintenance and "ses.3) 2lexible and powerf"l E"ery

capability.

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Disad'a(ta)es o* Relatio(al DataModel:-

1) ardware (verheads

#) ase-to-$esign capability leading tobad design&

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+I+< '7A+I(SI* :-') $A+A %($7&-

It is a logical database model! which hasa logical representation of data for anenterprise of b"siness establishment.

It is a collection of obects of similarstr"ct"res called an entity set.

+he relationship between entity sets is

represented on the basis of n"mber ofentities from entity set that can beassociated with the n"mber of entities ofanother entity set.

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It has one-to-one :1&1)! one-to-many:1&m)! many-to-many:n&m)

relationships .

+he following shows b"ilding bloc/s orsymbols to represent -' diagram.

ENTIT!SET

ATTRIBUTES

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'7A+I(SI*

7IL 5+DA++'I54+ A$

+I+< S+

MANDATOR!ONE

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%A$A+('