c Odds Rules

8/22/2019 c Odds Rules

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1.The Information Rule

All Information is explicitly andlogically represented in tables asdata values.


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2.The Rule Of Guaranteed Access

Every item of data must be logicallyaddressable with the help of a name,primary key value and column name.


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3.The Systematic treatment ofnull values

The RDBMS must be able to

support null values (these valuesare different are different fromzeros and spaces) to present

missing or inapplicableinformation.


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4.The Database Description Rule

A description of database is

manipulated using logical structureswith which data was defined theRDBMS. These are accessible to users

with appropriate authority and arestored in the dictionary


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5.Comprehensive Data Sub Language

According to this rule, the system mustthe following

Data definitionView definitionData manipulation

Integrity constraintsAuthorizationTransaction management operations


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6. The View Updating Rule

All views that are theoreticallyupdateable must also be updateable bysystem.


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7. The Insert and Update Rule

A single operand must hold good forall retrieval, update delete and insertactivities. This rule implies that all thedata manipulation commands must beoperational on sets of rows having a

relation rather than on a single row.


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8. The Physical Independence Rule

Application programs must remainunimpaired when any changes aremade in storage representation or

access methods.


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9. The Logical Data IndependenceRule

The changes that are should affect the

users ability to work with the data. Thechange can be splitting the table intomany more tables.


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10. The Integrity IndependenceRule

The Integrity constraints should bestored in the system catalog or in thedatabase as a table.


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11. The Distribution Rule

The System must be able to accessor manipulate the data that isdistributed in other systems.


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12. The Non-Subversion Rule

The non-subversion rule states thatdifferent levels of the language cannotsubvert or bypass the integrity rules and

constraints. To put it in simple words, ifan RDBMS supports a lower levellanguage then it should not bypass any

integrity constraints defined in thehigher level.


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Normalization theory is built the concept ofnormal forms.

Normalizations reduces redundancy.Redundancy is unnecessary repetition of data.It can cause problems with storage andretrieval of data.

During the process of normalization,dependencies can be identified, which cancause problems during deletion and updation.

Normalization theory is based on thefundamental notation of functional dependency.Normalization helps in simplifying the structureof tables.


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First Normal Form

consider an example, One employeehas different project codes. Hence the

Projcode is said to be functionallydependent on the attribute Ecode. Nowconsider an unnormalized data that isrepresented in the following Table.


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Ecode Dept Projcode Hours

101

343

987

Accounts

Admin

Sales

2040

4156782045

90101

6050924867


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A relational model does not permit orsupport such unnormalized tables. The datatable must be present atleast in the firstnormal form.

Ecode Dept Projcode Hours

101

101

101

343

343

987

987

Accounts

Accounts

Accounts

Admin

Admin

Sales

Sales

20

40

41

56

78

20

45

90

101

60

50

92

48

67


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Second Normal Form

In the previous form it was noted thatthere was redundancy of data, andhence the table was decomposed

withoutany loss of information. The problemsencountered here were:

Insertion:Employee details cannot berecorded until the employee is assigned

a project.


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Updation: The employee code anddepartment is repeated. Hence if anemployee is transferred to anotherdepartment, these changes must bereflected everywhere. Any omission

will lead inconsistencies.

Deletion: If an employee completeshis project, his record will be deleted

and details pertaining to thatemployee lost.


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Ecode Dept

101

343987

Accounts

AdminSales

Ecode Projcode Hours

101101

101343343987

987

2040

41567820

45

90101

60509248

67


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Third Normal FormA table is said to be in the third

normal form if it in second normalform and every non-key attribute isfunctionally dependent on just the

primary key. The primary key here isEcode. The attribute dept-code isdependent on dept. There is an

indirect dependence on the primarykey, which has to be noticed. It isillustrated in the following table.


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Ecode Dept Dept-code

101303

400500600777

FinanceSales

SalesAdminSystemsFinance

909906

906908901909


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Even here it was noted that there wereproblems during insertion, updation and

deletion. The relation is thus reduced asshown in the following table.

Ecode Dept

101303

400500600777

FinanceSales

SalesAdminSystemsFinance

Dept Dept-

code

FinanceSales

SalesAdminSystems

Finance

909906

906908901

909


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Each non-key attribute is wholly dependentonly on the primary key. Even the thirdnormal form did not satisfy the needs.Hence, a new form called theBoyee-Codd Normal from was introduced.

Boyee-Codd Normal FormThe third normal form was notsatisfactory for relations that had multiplecandidate keys, are unique for each row.Consider that another table that has fewother details, as shown in the followingtable.


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Cusno Cusname

100121280

PreethiJaikumar

Shalini

Here the candidate keys are cuscode, andcusname. The attribute cuscode and cusnameare unique for each row. Consider that tablethat has few other details, as shown in thefollowing table.


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Cuscode Cusname Itemcode Qty

100100121

280

PreethiPreethiJai Kumar

Shalini

191629

33

426

1

The attributes cuscode and cusname of theabove two tables can be used to link thesetables. These act as a foreign key in thesecond table. These tables can be reduced onorder to minimize redundancy. The tables are

shown below.


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Cuscode Itemcode Qty

100101121280

19162923

4261

Cuscode Cusname

100121280

PreethiJai KumarShalini

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