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Chapter 2Database System Design

(part II)

1

Based on G. Post, DBMS: Designing & Building Business Applications

University of ManitobaAsper School of Business

3500 DBMSBob Travica

Updated 2015

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Special Associations: Aggregation

Sale

Item

* contains *SaleIDSaleDateEmployeeID

ItemIDDescriptionlistPrice

• Many-to-many relationship: Each sale transaction contains many items, and each item can be included in many sale transactions (provided items are keyed generically -ItemID identifies a sort of things). • Item and Sale are loosely coupled.

• SaleID is the unique key (identifies one specific sale transaction),

Sale1 ItemAItemB

Note: This is called instance diagramand it might help you with visualizing multiplicity.Sale2 ItemC

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Special Associations: Composition(Part-Whole Relationship)

Association between the

whole class (Bicycle) and

part classes (Wheel,

Crank and Stem).

Two ways of displaying composition:

• The whole class is composed from part classes—it does not exist without certain parts.

• Parts have purpose as the parts of a specific whole—they live and die with the whole.

• Therefore, part classes and whole class are tightly coupled.

WheelWheelIDRimSpoke…

2

part of

Crank

CrankIDWeight

Stem

StemIDWeightSize

Bicycle

BicycleIDSizeModel Type…

1

1

A

Bicycle

SizeModel Type…

Wheel

Crank

Stem

B

• Typical use: Manufacturing, bill-of-materials

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Generalization

AnimalAnimalIDDateBornNameGenderListPrice

MammalAnimalIDLiiterSizeTailLength

FishAnimalIDFreshWaterScaleCondition

SpiderAnimalIDVenomousHabitat

{disjoint}

is_a Is_a Is_a

• Superclass is parent class, and sub-class is the child class that inherits from parent.

Association between theSuperclass (Animal) and Sub-Classes (Mammal, Fish,Spider).

Example: Modeling dataon animals sold in a pet store.

• Generalization/Specialization resembles hierarchical classification schemes.• Multiplicity is assumed: 1:1

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Inheritance

• Class Encapsulation of

– Data Attributes

– Methods (Behavior)

Account

AccountIDCustomerIDDateOpenedCurrentBalanceOpenAccountCloseAccount

Class name

Attributes

Methods

SavingsAccount

InterestRate

PayInterest

CheckingAccount

MinimumBalanceOverdraft

BillOverdraftFeesCloseAccount

Polymorphism

• Concept from Object Orientated Approach

Inheritance

• Properties:

– Parent class (Super-class) and Sub-classes – inheriting attributes & methods

– Unique attributes and methods in sub-classes (all listed)

– Polymorphism (variation of parent’s methods in children)

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Class Diagram of Pet Store System

Animal

CustomerSupplier

Merchandise

AnimalPurchaseOrder

MerchandisePurchaseOrder

SaleEmployee

*

1

*

1

1

* *

1

1

**

1

**

*

*

* 1*1

SaleItemMerchOrderItem

Each animal keyeduniquely.

Merchandise keyedgenerically.

Note – differences from the textbook: Names of some classes modified. Association names not included. Some other slight modifications.

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Pet Store Normalized Tables Diagram (Schema)

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Data Types (Domains)

Format of data and range of values.

Access SQL Server Oracle Text fixed variable memo

Text Memo

char, nchar varchar, nvarchar text, ntext

CHAR VARCHAR2,NVARCHAR2 LONG

Number Byte (8 bits) Integer (16 bits) Long (32 bits) (64 bits) Fixed precision Float Double Currency Yes/No

Byte Integer Long NA NA Float Double Currency Yes/No

tinyint smallint int bigint decimal(p,s) real float money bit

INTEGER INTEGER INTEGER NUMBER(127,0) NUMBER(p,s) NUMBER, FLOAT NUMBER NUMBER(38,4) INTEGER

Date/Time Date/Time datetime smalldatetime

DATE

Image OLE Object image LONG RAW, BLOB AutoNumber AutoNumber Identity

rowguidcol SEQUENCES ROWID

Common Type

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Computed Attributes

• Denote computed values. Written with a slash (/).

EmployeeNameDateOfBirth/AgePhone…

{Age = Today’s Date - DateOfBirth}

• Common example in business DB system: Sum=Item’s Sale Price * Quantity Sold

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Events & Triggers+

Generate Standing Purchasing Order.

Scroll down slides file.

Change in time:

ON (LastDayInMonth)

Change in user interface:

OnClickOfMouse

Notify Purchasing Manager.

Change in data:

ON (QuantityOnHand < 100)

Decrease Inventory count.

Change in organization :

Item is sold.

Code (program) invoked by events.*

Definition:

Some change in organization, data, time, user interface invoking execution of certain code (programs).

TRIGGEREVENT

+ Discussion in the book somewhat confusing.

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Rolling Thunder Bicycles: Package View

Sales Assembly

PurchasingLocation

Bicycle

Employee

• Package = A grouping of related elements to provide an overview of a database system.

• The way modern OO systems are designed and procured.

• Each package typically has more classes.

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Rolling Thunder Bicycles: Sales Package

CustomerCustomerIDPhoneFirstNameLastNameAddressZipCodeCityIDBalanceDue

CustomerTransaction

CustomerIDTransactionDateEmployeeIDAmountDescriptionReference

Retail Store

StoreIDStoreNamePhoneContactFirstNameContactLastNameAddressZipCodeCityID

Bicycle::Bicycle

BicycleID… CustomerID

StoreID…

1..1

0..*1..1

0..*

0..*

0..1 From Bicycle package