Database_Design_-_A_Practical_Guide

8/7/2019 Database_Design_-_A_Practical_Guide

1/25

arch 3: Database Design, a Practical Guide

Gus BjUNOXQG

Progress Exchange 2007

10-13 June, Phoenix, AZ, USA1

2007 Progress Software Corporation1

Database Design, a Practical Guide

Gus BjrklundWizard, Progress Software Corporation

Brandon GibbsManager, US-East, Solution Engineer

Progress Software Corporation


Rules are made to be broken

To every rule,there is an exception!


2/25


Gus BjUNOXQG




If you thought this talk was going to be aboutindexing

It isnt. Nor is it about performance.


Topics

Theory:

What is Database Design

Basic Elements

Representing the Model as Tables

Practice

An Example Some Other Topics


First, a little theory


3/25


Gus BjUNOXQG




What do we mean by databasedesign?

A process for defining a modelof a subset ofthe real1 world, then representing it as datain tables in a relational database

At least, thats the definition we will use forthe purposes of this talk.

1 Well, for small values of real, anyway.


Basic Elements

Just 3 Things:

Entities

Attributes

Relationships

What do we put in our model?

The entity-relationship model was described by Peter Chen in 1976.

See http://bit.csc.lsu.edu/~chen/chen.html


Basic Elements: Entities

Can be thought of as nouns

People

author, composer, performer, seller, buyer

Places

home, IP address, URL, destination, factory,store

Things

song, recording, instrument, car, invoice

Is telephone number a place or a thing?


4/25


Gus BjUNOXQG




Basic Elements: Attributes

Can be thought of as adjectives (but only loosely): Length

Color

Horsepower

Part number

Song Title

Publication Date

Size

Fabric

Owner

Is telephone number a attribute or an entity?

Entities have attributes


Basic Elements: Relationships

Can be thought of as verbs: has a

owns

contains

supervises

performs

called

sold

purchased

proved

Entities are connectedbyrelationships

Is telephone number a relationship?


Relationships have attributes too

In May, 1995,Andrew Wiles

publisheda proof

of Fermats Last Theorem


5/25


Gus BjUNOXQG




Relationships have attributes too

In May, 1995,Andrew Wiles

publisheda proof

of Fermats Last Theorem

entity

entity

relationship

attribute


What goes in an entity

Identifying attributes

Must be able to uniquely identify the entity

Can have more than one way to id

Id can be composite

Descriptive attributes

the values you need to keep track of generally should be simple, not complex


What to include in your model

The things your application has to keep track of Telephones, wires, switches

The actions your application or its users perform Make calls, send telephone bills, collect payments

Some attributes of the things and actions Originating number, date and time of call, duration, called

number

Keep it simple

Be accurate

Keep it up to date


6/25


Gus BjUNOXQG




What to include in your model

Consider the goals of the system Everything you include should be there for a

reason you can state

in no more than two sentences

Everything should have a clear name

if you cant name it, it doesnt belong

Talk to the stakeholders !!!


What to leave out of your model

The real world has properties that dontmatter (to your application)

The real world has relationships that dontmatter

Things happen in the real world that dont

matter Keep it simple

If you cant say why you need it, leave it out


Logical vs Physical Data Models

Logical entities often require multiple tables torepresent them Tables can be thought of as logical or physical

It depends on your point of view

There is also the physical storage database layout storage areas

data extents

disks

etc.

We arent going to talk about the physical databaselayout

We will talk about tables


7/25


Gus BjUNOXQG




Mapping Your Model to aDatabase

Entities become tables Identifiers become indexes

Attributes become columns

Data types: pick appropriate

Relationships become tables or foreign keys

Simply put,


In theory, there is no difference betweentheory and practice, but in practice there is.

Jan van de Snepscheut


Now for some practice.


8/25


Gus BjUNOXQG




An example

Music store Buys compact disc recordings from

distributors

Has inventory

Allows customers to search for what they want

Maybe in an in-store kiosk or on the web

Sells compact discs to customers


What should we do first?


Activities

We buy discs from a distributor

Orders are sent to a distributor

Orders are delivered to the store

Orders may be cancelled

We sell discs to customers in sales transactions

Customers buy discs in sales transactions

Customers search for what they want to buy

Which of these must be remembered by the system?


9/25


Gus BjUNOXQG




What do we need to keep track of

Discs we have Discs we sold

Discs we know about and can get

Discs we have ordered

Information needed to do our income tax what we paid for stock

when we bought it

what we sold it for

when we sold it


Disc entities

UPC Code: 8697-07416-2

Manufacturer: Sony BMG

Cost to us: $ 2.00

Price charged: $ 17.95

Tax charged: $ 0.80

Date purchased: March 19, 2007 Date sold: June 9, 2007


Disc table might look like this

upc manuf cost price tax datePurch dateSold

86 97 -0 7416-2 Sony BMG 2 .00 17 .95 0. 90 20 07-03-19 200 7-06-09

8697-07416-2 Sony BMG 2.00 ? ? 2007-06-09 ?

314-510347- 2 Island Rec or ds 2 .21 15.95 0 .80 2006- 01-12 2007- 02-14

314-510347-2 Island R ecords 2.21 ? ? 2006-01-12


10/25


Gus BjUNOXQG




Whats wrong?

Is upc a unique identifier? Might have bought from a distributor

Have no information about what is on the disc How do customers search?

Dont know when disc was made

Could be more than one tax jurisdiction provincial tax, city tax

Dont know if disc is on order

Dont know who bought it

Duplicated data

Etc., etc.


Disc entities take 2

UPC Code: 8697-07416-2

Manufacturer: Sony BMG

Dist ri butor : Bob s Wholesale CDs

Cost to us: $ 2.00

Price charged: $ 17.95

Tax charged: $ 0.80

Date ordered : March 19, 2007

Date received: March 20, 2007

Date sold: June 9, 2007 Disc Title: The EssentialJoshua Bell

Artist: Joshua Bell

Track 1: Danse Russe

Tr ack 2: Vi olin Concerto in E Minor

Tr ack 3: Nocturne in C-shar p Minor

etc.


Example: Now Whats wrong?

This is getting messy

Activities combined with discs attributes

Have duplicated information

How many tracks can there be?

What if there is more than one artist?

Dont have all the information a customermight want to use to search


11/25


Gus BjUNOXQG




Discs revisited

Discs have titles Discs have pictures on the cover

Discs contain tracks

Discs are made by manufacturers

Discs are purchased from distributors

Discs are ordered from distributors

Discs are delivered to the store

Discs are sold to customers


Discs contain tracks

Tracks contain songs

Tracks occur in order

Tracks have a duration

Songs are performed in performances

Songs have performers (usually)

Songs have composers

Songs have names (titles)

Songs have a key (but not always)

Performances are done by performers

Performers can be groups (bands, orchestras, etc.)

Performances are performed in a location or venue


We seem to need these entities

Discs

Manufacturers

Distributors

Orders

Customers

Inventory

Tracks

Songs

Performers

Groups ?


12/25


Gus BjUNOXQG




Songs have names (titles).

Are names properties of songs?

Or are they entities related to songs?

Or are they something else?


Song data (track 1)

Title Danse Russe from Swan Lake, Op.20

Time 4:30

Composer Peter Tchaikovsky

Category Classical, v iolin, orchest ra

Performers Joshua Bell, Michael Tilson Thomas,

Berlin Philharminic OrchestraTrack number 1

Disc upc 8697-07416-2


Song data (track 2)

Title Violin Concerto in E Minor, Op. 64

Time 6:27

Composer Felix Mendelssohn


Performers Joshua Bell, Sir Roger Norrington,Camerata Salzburg

Track number 2

Disc upc 8697-07416-2


13/25


Gus BjUNOXQG




Performance data


Time 6:27





Performance data take 2


Time 6:27




PerformanceDate

?

PerformanceLocation

?


Performer data

id name

1 Joshua Bell

2 Sir Roger Norrington

3 Camerata Salzburg

4 Michael Tilson Thomas

5 Berlin Philharmonic

6 Bono

7 The Edge

8 Adam Clayton

9 Larry Mullen


14/25


Gus BjUNOXQG




Performance to PerformerRelationship

performance id performer id

1 11 2

1 3

1

2 1

2 4

2 5

2

325 6

325 7

325 8

325 9


Performance data take 3

Performance id 2


Time 6:27




Track to PerformanceRelationship

Disc up c Track Num Performance id

8697-07416-2 1 1

8697-07416-2 2 2

314-510347-2 1 325

h 3 D t b D i P ti l G id


15/25


Gus BjUNOXQG




Relationships (so far):

disctrack

track

track

trackperformance

performance

performance

performance

performer

performerone to one

one to many

many to many


What happened to Songs?


Relationships (take 2):

disctrack

track

track

tracksong

performance

performance

performance

performer

performer

one to one

one to many

many to many

performance

performance

performance

song

one to many

arch 3: Database Design a Practical Guide


16/25


Gus BjUNOXQG




Relationships (take 3):

disc

track

track

track

performance

performance

performance

performer

performer

song

song

song


What aboutbusiness entities

?

Where are they

?


Business entities

disc

track

track

track

performance

performance

performance

performer

performer

song

song

song

arch 3: Database Design a Practical Guide


17/25


Gus BjUNOXQG




Business entities

disc

track

track

track

performance

performance

performance

performer

performer

song

song

song


Business entities

disc

track

track

track

performance

performance

performance

performer

performer

song

song

song


Should you use arrays?



18/25


Gus BjUNOXQG




Indexes

Enforce uniqueness

Make searches faster

Enable fast retrieval of entities by theiridentities

Enable finding entities with certain attributes


What indexes do we needfor the music store database?


Tables

0) Discs1) Tracks2) Songs3) Performers4) Performances5) Tracks of discs6) Performances of songs7) Performers of performances



19/25

g ,

Gus BjUNOXQG




What indexes do we need

0) Indexes for identifying attributes1) A unique row identifier2) Indexes for the queries you will do


What should we do next ?


Other Topics

Normalization

Unique keys

Word indexes

Naming

Customisation



20/25

Gus BjUNOXQG




Normalization

Oversimplified, it means: Dont duplicate data

Attributes should be simple have only one value

be necessary

not derived data

dont repeat

Complicated attributes are often entities intheir own right For example, addresses might be


Unique keys

EVERY table must have a unique key

EVERY row needs a unique identifier that never changes even if moved to another database

(i.e. if you replicate)

Often, users dont need to see it

Use a UUID or sequence or maybe datetime

Unique key is the ONLY way to identify rows

unambiguously ROWIDs are temporary and can change

Use the same method throughout Youll be glad you did


Word indexes

Can be used to hold multiple status orattribute values Conflicts with normalisation

Flexible

Easy to add new ones

Queries are fast

Example: Category: classical, violin, orchestral, concerto



21/25

Gus BjUNOXQG




Naming

What is in the column GL01262 ?

Good names are crucial to understanding


Naming

Table and column names should have clearmeanings everyone can understand GL01262 vs dateEntered

Names with dashes cause inconveniencewith SQL order-date

Booleans should be named for truth value backOrdered

No double negations notOutOfStock

Good names are crucial to understanding


Making tables customizable

Spare columns

Separate table with spare columns

Separate table with name/value pairs

We will look at 3 ways:


G Bj NO G


22/25

Gus BjUNOXQG




Spare columns in table

custnum name city

001 Bob Phoenix

002 Alice Boston

003 Eve Denver

extra1 extra2 extra3

frozen ? 0.0

? 125.46 0.12

? ? ?


Spare columns in table

custnum name city

001 Bob Phoenix

002 Alice Boston

003 Eve Denver

extra1 extra2 extra3

frozen ? 0.0

? 125.46 0.12

? ? ?

What data types should you use?How many spare columns?Wasted columns when not usedHow do you know what each spare got used for?How do you know how many unused spares you have?


Separate table for spare columns

custnum name city

001 Bob Phoenix

002 Alice Boston

003 Eve Denver

custnum extra1 extra2 extra3

001 frozen ? 0.0

002 ? 125.46 0.12


Gus BjUNOXQG


23/25

Gus BjUNOXQG




Separate table for spare columns

custnum name city

001 Bob Phoenix

002 Alice Boston

003 Eve Denver

custnum status owed discount

001 frozen ? 0.0

002 ? 125.46 0.12


Separate table with name/valuepairs

custnum name city

001 Bob Phoenix

002 Alice Boston

003 Eve Denver

custnum name value

001 status frozen

002 owed 125.46

002 discount 0.12


Modeling Tools

PCase

Enterprise Architect

Power Designer

ConceptDraw

Erwin

Rational

Pencil and paper !

Blackboard !


Gus BjUNOXQG


24/25

Gus BjUNOXQG




Summary

Understand the requirements

Leave out what is not needed

Review the design with stakeholders

Evolve the design as changes come up

Test to make sure it works

Can it do everything that is needed?

Does it perform adequately?

Expect changes to come


Homework

Papers Wiles, A.: "Modular elliptic curves and Fermat's Last

Theorem, Annals of Mathematics 141 (3): 443-551

Chen, P.: The Entity-Relationship Model -- Toward aUnified View of Data, ACM TODSVol 1, No 1, 1976

Wikipedia articles to start from: entity-relationship model

data model

Books: Teorey, Lightstone, Nadeau: Database Modelingand

Design, Morgan Kaufmann.


Questions


Gus BjUNOXQG


25/25

Gus BjUNOXQG




Documents

Database_Design_-_A_Practical_Guide