Database Design

Sections 4 & 5Subtype, Supertype, Mutually exclusive, non-transferability, transferable, 1:1, 1:M, M:M, Redundant, Intersection entity, Barred relationship, First Normal Form (1NF)

DJs on Demand – Partial ERD

Reserved Words

A reserved work is one that has a specific meaning and function in the computer system, language, or database.

Examples: NULL DATE DISTINCT

Video Store – example 4.1.7

Identify business rules Construct ERD Class activity

Video Store Matrix

ACTOR CUSTO-MER

MOVIE TAPE

ACTOR Featured in

CUSTO-MER

The renter of

MOVIE The feature of

On

TAPE Rented by A copy of

Video ERD

featured in

TAPEnumberformat

MOVIEid

titlecategory

ACTORstage namereal name

CUSTOMERmembership

numberlast namefirst name

phone number

a copy of

on

the feature ofrented by

the renter of

Use Source Documents

Source document assist in identifying entities, attributes, and relationships

Global Fast Food

Identify entities

Possible solution

ORDER#number

*date*time

STAFF#id

*first name*last name

*date of birth*salary

FOOD ITEM#number

*description*price

handle

handled by

list

listed on

Subtype & Supertype

Supertype (entity) can be subdivided into Subtypes

Example:

JOBmanager

clerksales

support

Attributes

Supertype can have attributes at supertype level

Attributes at supertype level are for all subtypes

Subtypes can have own attributes for only that attribute

Example

EXAM#number

*description*weight*date

*grade for written component

MIDTERM*grade for

oral presentation

FINAL*extra pts for opt. paper

QUIZ

BONUS QUESTIONS

STUDENT

included in

included

taken by

Global Fast Food Employees

STAFF is an entity and supertype What are the attributes of STAFF? What subtypes exist in STAFF?

Are there any attributes in any of the subtypes?

Example 4.3.9

AUTOMOBILE subtypes are not mutually exclusive

AUTOMOBILE possible solution BUILDING subtypes have problem of

not being exhaustive, should be minimum of 2 types

Business Rules Recognize if Business rule is implemented

by the data model or by programming Example:

Only an employee with a title of manager can manage other employees

The event planner must contact the customer before the DJ can be assigned

Business rules can changed as society changes or business leaders feel change needed

Business rule types Structural

Must be entered at time of initial data entry Example: When ORDER entered a staff id must

be entered Does not require code written to enforce

Procedural Work flow related Programmed validation is procedural constraint

Generally need to write code Example: Commission can not be > 25% of

salary

Each entity has

Name Optionality Cardinality Transferability

Relationship transferability Rules established for the purpose such as

safety, efficiency, or increased profit Example: Airline tickets

can be transferable or non-transferable? Non-transferable means also not updatable symbol used to denote non-

transferable blood type is non-transferable

Non-transferable relationship

Orders are non-transferable Resolution would be to cancel order

and create new order

CUSTOMER ORDER

place

placed by

Example 5.1.6 #1

Each town may be the birthplace of many people. Each person must be born in one and only one town.

PEOPLE TOWNbirthplace for

born in

Relationship types

One to One (1:1) One to Many (1:M) Many to Many (M:M)

One to One relationship

Usually few of these relationships Often mandatory at one side If mandatory at both ends be aware,

it might be a error. Possible should be only one entity not two

PERSON BYCYCLE

ride

ridden by

One to Many

Most common type are mandatory on one side and optional on the other

Mandatory at both ends models entities that cannot exist without each other

ORDERORDER TYPE

One to Many example

TAX RETURNTAX REPORT

LINE

BAND MUSICIANcomposed of

belong to

composed of

entered in

Many to Many

Often common in initial version of ERD

Later stage of design converted to other type

STUDENT TEACHERlearn from

educate

Redundant relationship

Redundant relationship is one that can be derived from another relationship in the model

Many to Many Relationship Resolution

All M:M relationships must be changed to a set of 1:M and M:1 relationship

Insert a transition entity between Occurs when you go from conceptual

model to design model

Example: M:M with Intersection Entity

STUDENT COURSE

REGISTRATION

Resolving M:M with Intersection

Create an intersection entity If you can’t find a good intersection

entity create one by concatenate two entities together

Example

PARTNER EVENT

WORK ASSIGNMENT (PARTNER_EVENT)

Normalization

To make sure you don’t store the same data twice in the model

Also, that you store the data in the correct place

We will cover the first 3 normal forms.

First Normal Form (1NF)

First Normal Form requires that there be no multivalued attributes and no repeating groups.

To check for 1NF, validate that each attribute has a single value for each instance of the entity.

In other words: “One value per Attribute”.

Example 1NF

This has multiple values for the classroom.

SCHOOL BUILDING#code*name

*address*classroom

Example 1NF

Telephone is a multvalued attribute that could be an Entity. Ie. Home, work, mobile, fax etc.

Not all Employees have multiple phones, so there would eliminate multiple NULL values.

EMPLOYEE#id

*name*address

.

.º telephone

º salary

Review 1NF examples

Look at the 4 examples on 5.4.4