Databases

Week 5

LBSC 690

Information Technology

Agenda

• Questions

• Relational database design

• Implementation using Microsoft Access

Relational Databases• Tables represent relations

– Name, project– Name, email address, phone number

• Relations can be “joined”– Name, project, email address, phone number

• Relations can be “projected”– Name, email address

• Relations can be “restricted”– Name = “Doug Oard”

Why use Join?

• Forces consistency– Doug Oard, project 18, oard@glue, 57590

– Doug Oard, project 22, oard@wam, 57590

• Limits the chance of error– Doug Oard, project 18, oard@glue, 57590

– Doug Oard, project 19, oard@glue, 57490

• Avoids lots of duplicated entry and updates• Can save a lot of storage space

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

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

Example of a Join on “Team”

Name Team Team Project Name Team Project

Chris

Chris

Camile

Eileen

Natalie

David

Tonya

Skip

A

A

A

B

C

B

C

C

A

B

C

Database

Web

Web

A

A

A

B

C

B

C

C

Chris

Chris

Camile

Eileen

Natalie

David

Tonya

Skip

Database

Web

Web

Web

Web

Web

Database

Database

Project to Keep Two Fields

Name Team Team Project Name Project

Chris

Chris

Camile

Eileen

Natalie

David

Tonya

Skip

A

A

A

B

C

B

C

C

A

B

C

Database

Web

Web

Chris

Chris

Camile

Eileen

Natalie

David

Tonya

Skip

Database

Web

Web

Web

Web

Web

Database

Database

Restrict to Web Pages

Name Team Team Project Name Project

Eileen

Natalie

David

Tonya

Skip

A

A

A

B

C

B

C

C

A

B

C

Database

Web

Web

Chris

Chris

Camile

Eileen

Natalie

David

Tonya

Skip

Web

Web

Web

Web

Web

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)

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

Exercise Goals

• Identify the tables you will need– 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

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

One Possible Answer• Surely you didn’t expect this in the notes :)

Flight: Flight Number, Origin, Destination, Departure Time, Arrival Time, Available Seats, Company Name, PricePassenger: Passenger Number, Name, Address, Phone Number

Booking: Flight Number, Passenger Number

Company: Company Name, Company Address, Company Phone

Passenger calls: Join: Flight, Company Project: Departure Time, Company Phone Restrict: Origin, Destination, Available Seats>0Company calls: Join: Flight, Passenger, Booking Project: Flight Number, Name, Phone Number Restrict: Company Name

Tables:

Queries:

Microsoft Access

• Start Access– 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

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

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

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

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

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

• Join is the most important concept– Project and restrict just remove undesired stuff

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