dIntroduction to Databases

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Introductionto Databases


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A Brief History

The land when applications ruled the world An accounting program stores accounting data A marketing program stores marketing data An operations program stores marketing data

Databases were part of the applicationprogram that nobody ever noticed (or

changed)


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History ctd.

If a customer changes an address, it has tobe updated in each program

Accounting Marketing perations


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Problems with the Applications Approach Data Storage

!edundancy and duplicate data Data Updating

"hanges or additions must be performed multiple times Currency of Information

#otential problem of failing to update all affected files Task-Data Dependency $iles structured, formatted and arranged to suit a specific need% &ach user maintains a separate file for their own use Individual data files are not related to other files thus integration is difficult 'sers inability to obtain additional information as needs change Difficult to share data 'sers own rather than share data


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The Database Grows Up

Moores law says &very * years one of two things will happen

+oull get * the computer storage memory for the same price The price of your current memory will be cut in half

-ith more disk storage, companies were able to save more

data All of this data put the focus on the database Databases were developed as standalone systems Databases became the engine behind application programs -hy not make one database for the application programs to

feed off of. "ustomer address only gets changed once All application programs see (accounting, marketing, ops)


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One Database

/tandardi0ed Data $ormat A 1data store2 for the

various applications to pullfrom

A c c o u

n t

i n g

M a

r k e t i

n g

p

e r a

t i

o n s


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The %elational Database• Mathematical mapping of data

• 4o more parent to child relationships• More fleible for business

• The defacto standard in databases

• /trengthened by the rise of /=>

•

!elational Databases of note• racle

• I:M

• my/=>

• /A#

• More relational database history

• http??www%nap%edu?readingroom?books?far?ch8%html

&%$% "odd

http://www.nap.edu/readingroom/books/far/ch6.htmlhttp://www.nap.edu/readingroom/books/far/ch6.htmlhttp://www.nap.edu/readingroom/books/far/ch6.htmlhttp://www.nap.edu/readingroom/books/far/ch6.html


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&lements of a %elationalDatabase

Queries(Join Tables to Get Required Fields)

Reports(make it pretty)

Table(House Data)

Table(3ouse Data)

Table(3ouse Data)

Table(3ouse Data)

… … …

Forms(User Friendly Way to nter Data)


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'omponents of the Dataodel &ntities

!esources &vents

Agents !elationships

66

6M, M6 MM


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&ntities

Identify resources, events and agents (found on rightside of verview Activity Diagram) "ommon resources

Inventory "ash Accounts

"ommon events #urchase, !eceipt of Inventory, #ay ;endor !eceive rder, #ick @oods, /hip rder, :ill, !eceive "ash

"ommon Agents "ustomer, ;endor, &mployee


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%elationships

!elationships between entities are determined byanaly0ing the activity diagram (or narrative ifdiagram not given) If have an ideal activity diagram, all relationships

known If a relationship eists < then the tables are linked ften relationships eist between

resources and events

events and agents events and events

To link tables, need to understand the 1type2 ofrelationship between the tables 5 called cardinality


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'ardinalities

The cardinality is the degree to whicheach entity participates in the relationship

>ets start by looking at some relationships

between entities so that we can see why they are set up that way


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One(to(one relationship

Employee Spouse

1 1

If one instance of Employee, how many Spouses

are possibly related? Put answer by Spouse.

If one instance of Spouse, how many Employees

are possibly related? Put answer by Employee.


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any(to(one relationship

Employee DepartmentM 1

If one instance of Employee, how many

Departments are possibly related? Put answer by

Department.

If one instance of Department, how manyEmployees are possibly related? Put answer by

Employee.


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One(to(any relationship

Department EmployeeM1

If one instance of Employee, how many

Departments are possibly related? Put answer by

Department.

If one instance of Department, how many

Employees are possibly related? Put answer by

Employee.


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any(to(any relationship

Sale ShipmentMM

If one instance of Shipment, how many Sales are

possibly related? Put answer by Sales.

If one instance of Sale, how many Shipments are

possibly related? Put answer by Shipments.


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Practice#Assume most typical)"eneralcase$

Tetboo! "lass

Payment "ashier

#endor Purchase

$rder

%ecei&in'%eport

%ecei&in'"ler!

In&oiceIn&entory

Item


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Di*in" Deeper

Define attributes (fields) foreach entity

"ustomer

"ustomerID

>ast4ame

Address

B%

:illingInvoiceID

InvoiceDate

"ustomerID

B%


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,orei"n +ey %ules

A $oreign key is reCuired for each 66 and6M relationship

$or 6M, the foreign key is put in the 1M2 side

consisting of the primary key from the tableon the 162 side

$or 66 events, the foreign key is put in thetable representing the second event and

points back to the first event%


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- relationships

-e need to create a table between all MMrelationships using the #s of the two tablesas a composite # of the table in the middle


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Tables and %elationships

Inventory Table

Prod no.

Description Invoice no.

Prod no.

(ty. ordered

Invoice no.

)nit Sale Price

In&oice Date

*ame

Std. Price

Sales Clerk Table

Inventory-Sale Table Sale Table

(ty. shipped Total Sale

Customer TableAccount no.

*ame

Clerk Emp. no

+ttentionStreet

"ity

ip

State

Foreign key

Primary key

Clerk Emp. no

Account no.

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