Databases
CS 110
Fall 2005
Homework


Read “Introduction to Access” from
text
Next Tuesday: turn in index card
with three questions about reading
Databases
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
Become common in 1970s
If spreadsheets crunch numbers…
databases crunch information
Aren’t numbers information?
Managing Information

What is information?
• How do I get to the Rotunda from here?
• Is there a baby panda at the zoo?
• When does the next bus come by?
• What’s your phone number?
These aren’t numerical questions
Logical Relationships

How do I get to the Rotunda from
here?
• Consider taking all actions from here
1.
2.
3.
Where do I end up?
Am I at the Rotunda?
Consider taking all actions from there
1. Where do I end up?
2. Am I at the Rotunda?
3. Repeat…
Logical Relationships

Consider taking
all actions from
here
1. Where do I end
up?
2. Am I at the
Rotunda?
3. Consider taking all
actions from there
1.
2.
3.
Where do I end
up?
Am I at the
Rotunda?
Repeat…
Logical Relationships
I
H
G
C
E
A
F
B
D
A
B
C
D
E
F
G
H
I
B, C
A, E
A, D, E, H
C
B, C, F, G
E, G
E, F
C, I
H
Logical Relationships

Is there a baby panda at the zoo?
1. Create list of all animals at the zoo
2. Look for panda in the list
3. Return TRUE or FALSE
Logical Relationships

When does the next bus come by?
1.
2.
3.
4.
Get bus table
Organize it by location
Sort by time
Find entry closest to current time that
is in the future
What kind of tasks are being
repeated?

Find affiliated entries that follow
specific rules
• B must be reachable from A
• Name must be panda
• Time must be in the future
Database Examples

Tables – The phone book
• A column of names
• A column of addresses
• A column of phone numbers
Database Examples

Hierarchical – A family tree
• Mary is mother of John
• John and Sue are parents of
Liz
• John and Sue are parents of
Laura

Derived information
• Mary is John’s mom
• John does not have another
mom
• Laura and Liz are siblings
Mary
John
Liz
Laura
Some Practical Matters

Tables and hierarchical databases are
monolithic and cumbersome
• Updating
• Storing
• Disseminating
Examples
Telephone Tables

Someone forgot to include the zip
code in the phone book
• Add a column to the database and mail
a new phone book to everyone?
• Send an update book which contains
only names and zip codes?
Family Hierarchy

Through remarriage, a person can
have multiple mothers
• Family tree structure must be adjusted
to permit multiple moms
• Entire tree must be rewritten
• Break the hierarchical organization
• Permit everyone to have “parents” and
define this in greater detail elsewhere
Relational Databases

Multiple Tables!
• Business records




A
A
A
A
table
table
table
table
of
of
of
of
products in inventory
customer contact info
product suppliers
current orders
• customers -> products
• customers -> products -> supplier
• credit card # -> customers -> products
Vocabulary

Field: a basic fact
• There is a customer named Thomas
• There is a phone number: 924-HOOS

Record: A set of fields
• Customer names and phone numbers are
related
• 924-HOOS --- Thomas

Table: A set of records
• Students at UVa listed with phone numbers

Database: A set of tables
Power of Relational DBs

Lots of tables with relationships
between them
Power of Relational DBs

Efficiency and flexibility in storing
and retrieving information
• Easy to add / remove

New records and new descriptors
• Fast to retrieve
• Easy to customize for greater speed
• Easy to control security


Only one writer at a time (ATM)
Exclude some readers (credit reports)
Challenges of Relational DBs


They become very complex
Complexity leads to errors
• Stale relationships

The area codes for C’ville are updated in one table
but not another
• Faulty fields in relationships

A person is related to two different area codes
There’s an art to architecting databases that
reduce these problems
Commercial Systems

Oracle-PeopleSoft
SAP
Microsoft
Siebel

Structured Query Language (SQL)
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