1. Class 5 LBSC 690 Information Technology
Databases
Class 5
LBSC 690
Information Technology

2. Agenda Questions Databases Programming Concepts
Relational database design
Implementation using Microsoft Access
Programming Concepts
The mythical person-month
Object oriented programming

3. Relational Databases Tables represent relations
Name, project
Name, address, phone number
Relations can be “joined” (**most important**)
Name, project, address, phone number
Relations can be “projected”
Name, address
Relations can be “restricted”
Name = “Doug Oard”

4. Why use Join? Forces consistency Limits the chance of error
Doug Oard, project 18, 57590
Doug Oard, project 22, 57590
Limits the chance of error
Doug Oard, project 19, 57490
Avoids lots of duplicated entry and updates
Can save a lot of storage space compared to a flat file

5. Problems with Joins Data modeling for joins is complex
Taught in LBSC 670
Joins are expensive to compute
Both in time and storage space
But it is joins that make databases “relational”
Projection and restriction also used in flat files

6. Key Fields Primary Key uniquely identifies line to join
May group several fields to get a unique key
Social security number
First and last name
“Foreign” key must appear in the other table
But it need not be unique there
Join makes a new table
Line specified by foreign key is tacked on

7. Example of a Join on “Team”
Name
Team
Team
Project
Name
Team
Project
Chris A A
Database
Chris A
Database
Chris A B
Web
Chris A
Database
Camile A C
Web
Camile A
Database
Eileen B
Eileen B
Web
Natalie C
Natalie C
Web
David B
David B
Web
Tonya C
Tonya C
Web
Skip C
Skip C
Web

8. Keep Just Two Fields Name Team Team Project Name Project Chris A A
Database
Chris
Database
Chris A B
Web
Chris
Database
Camile A C
Web
Camile
Database
Eileen B
Eileen
Web
Natalie C
Natalie
Web
David B
David
Web
Tonya C
Tonya
Web
Skip C
Skip
Web

9. Restrict to Web Pages Name Team Team Project Name Project Chris A A
Database
Eileen
Web
Chris A B
Web
Natalie
Web
Camile A C
Web
David
Web
Eileen B
Tonya
Web
Natalie C
Skip
Web
David B
Tonya C
Michelle
Skip C

10. How to Split Tables The idea is to remove redundancy
For simple problems (like the homework)
Start with “binary relationships”
Pairs of fields that are related
Group together wherever possible
Add keys where necessary
For more complicated problems
Entity relationship modeling (LBSC 670)

11. FlightFinder Exercise
Design a database to match passengers with available flights on corporate jets
Companies phone in available seats
They want to know about interested passengers
Passengers call up looking for flights
They want to know about available flights
These things happen in no particular order

12. Exercise Goals Identify the tables you will need Design the queries
First decide what data you will save
What questions will be asked?
Then decide how to group it into tables
Start with binary relations if that helps
Design the queries
Using join, project and restrict
Add primary and foreign keys where needed

13. Exercise Logistics Work in groups of 3 or 4
Brainstorm data requirements for 5 minutes
Do customers care about the price?
Do companies care what passengers weigh?
Develop tables and queries for 15 minutes
Don’t get hung up on one thing too long
Compare you answers with another group
Should take about 5 minutes

14. One Possible Answer Surely you didn’t expect this in the notes :)
Tables:
Flight: Flight Number, Origin, Destination, Departure Time,
Arrival Time, Available Seats, Company Name, Price
Passenger: Passenger Number, Name, Address, Phone Number
Company: Company Name, Company Address, Company Phone
Booking: Flight Number, Passenger Number
Queries:
Passenger calls: Join: Flight, Company
Project: Departure Time, Company Phone
Restrict: Origin, Destination, Available Seats>0
Company calls: Join: Flight, Passenger, Booking
Project: Flight Number, Name, Phone Number
Restrict: Company Name

15. Microsoft Access Start Access Name your database planes.mdb in M:\
Icon in the Microsoft Office folder
Name your database planes.mdb in M:\
Click “Table” and then “New”
Select “New Table”
Table wizards can be helpful (query wizards are not)
Enter the fields

16. Entering Fields Field Names must be unique in a table
Select field type from a menu
Use date/time for times
Use text for phone numbers
Use right mouse button for primary key
Save the table when you’re done
That’s when you get to name it
Exit, then reselect to enter the data

17. Building Queries Copy N:\share\class\flight.* to M:\
Select “Queries” then “New”
Skip the query wizard
Choose two tables
Flight and Company
Pick each field you need using the menus
Unclick the X to “unproject”
Enter a criteria to “restrict”
Save, exit, and reselect to run the query

18. Fun Facts about Queries
Joins are automatic if field names are same
Otherwise, drag a line between the fields
Sort order is easy to specify
Use the menu
Queries form the basis for reports
Reports give good control over layout
Use the report wizard - the formats are complex

19. Other Things to Know “Referential integrity” assures joins will work
Need to specify this when defining tables
Forms manage input better than raw tables
Invalid data can be identified when input
Graphics can be incorporated

20. Key Ideas Databases are a good choice when you have
Lots of data
A problem that contains inherent relationships
Design before you implement
This is just another type of programming
The mythical person-month applies!
Join is the most important concept
Project and restrict just remove undesired stuff

21. Database Projects Design for large amounts of data
Must use multiple tables
Need a plan for long-term maintenance
How will data be removed?
Attention to the user interface
Forms and reports
Web interfaces are hard
Enough content to verify proper operation

22. Software Software models aspects of reality Examples
Input and output represent the state of the world
Software describes how the two are related
Examples
Ballistic computations
Homework 6
Alta Vista
Microsoft Word

23. Programming Languages
Used to specify every detail of the model
Special purpose
Able to specify an entire class of models
Spreadsheets (Excell, Quatro Pro, ...)
Databases (Access, Paradox, ...)
General purpose
Able to specify any possible model
Pascal, C, Java, ...

24. The Mythical Person-Month
If it would take one person three months, why does it take four people SIX months?
Four causes
It wouldn’t have taken 3 months anyhow!
Partitioning strategy
Training time
Communications effort

25. How long will it take? Rules of thumb
1/3 specification
1/6 coding
1/2 test planning, testing, and fixing!
Add time for coding to learn as you go, but don’t take time away from the other parts!
Reread the section on “gutless estimating” if you are tempted

26. Training Time Simple Example
Full time person = 2,000 hours/year
Part time person = 288 hours per year
No training -> 7 part time people
With training -> 10 part time people
Learning the specification takes lots of time
Learning organizational “rules” takes longer

27. Communications Sort of like continuous training
Who needs to know what I just learned?
Can be minimized by good partitioning
Limit the number of interfaces
Can be facilitated by computers
Asynchronous communication techniques
, BBS, voice mail

28. History of Programming
Machine code
Zeroes and Ones
Assembly language
“Assembler” changes names to machine code
High-level languages
“Compiler” translates math to machine code
Independent of machine “architecture”
FORTRAN, COBOL

29. History of Programming
Structured Programming
Group instructions into meaningful abstractions
C, Pascal
Object oriented programming
Group “data” and “methods” into “objects”
C++, Java

30. Object Models Represent facts about the world as “data”
Combine data into “data structures”
Data structures model things
Represent actions using “operations”
Combine operations into “methods”
Methods model what can be done to things
“Classes” are data structures with methods
Classes model aspects of reality

31. A Simple Example Data: Height, Weight, Shoe size
Data structure: All three together
Operations: Multiply, Divide
Method: Shoe size=4*Weight/Height
Class: Method & data structure

32. Instances Classes actually model kinds of things
“person” in the example is a class
Objects are instances of a class
Object representing me is an instance of person
Object Oriented Programming
Define classes (data structures and methods)
Create objects
Perform some methods

33. Data Types int float char boolean
Like integers, but there is a biggest and smallest
float
Like real numbers, but there are a finite number
char
Any character in any language (UNICODE)
boolean
True or false

34. Data Structures Arrays Structures Lists of some type of data
Every element must be the same type
Each is assigned a number (0, 1, 2, ...)
An array of type “char” is called a “string”
Structures
Groups of (possibly) different data types
Each must be given a name by the programmer

35. Operations Same idea as methods - int produces int
But applied to data types rather than structures
- int produces int
int + int produces int
int * float produces float
int < int produces boolean
char == char produces boolean

36. Making Methods Actions can be operations or methods
Three ways to combine actions
Sequential (...; ...)
Conditional (if...then...else)
Loop (do...while, for ...)
Every possible model can be built this way!

37. Java Objects Represent things in the real world
Those things may be fairly abstract, though
Encapsulate data and methods
Data are the facts you seek to model
Methods represent actions
Classes are types of objects
When instantiated, you get an individual object

38. Java Data Types boolean int float char True or false
Like integers, but there is a biggest and smallest
float
Like real numbers, but there are a finite number
char
Any character in any language (UNICODE)

39. Java Data Structures Array String A list of things
Every element must be the same type
Each is assigned a number (0, 1, 2, ...)
String
An array of characters
Methods are provided for printing, etc.

40. Java Operations Things you can do to data Examples:
int < int produces boolean
char == char produces boolean
int + int produces int
int * float produces float
- int produces int

41. Java Statements Assignment Call to a method
numberOfBirds = numberOfHawks + numberOfOrioles;
Call to a method
airForceOne = new Airplane(“747”);
Altitude = aifForceOne.readAltitude();
Return a valule from a method
return numberOfBirds;

42. Combining Statements Three ways to combine statements
Sequential (...; ...)
Separate each with a semicolon (statement1; statement2)
Group using braces ({statement1;statement2})
Conditional (if ... then ... else or try ... catch ...)
Loop (do ... while, for ...)
Every possible model can be built with these 3!