Introduction to Data Bases

What is (are) Data

• Information? - no• Information is PROCESSED data• Data are facts - descriptions of an entity,• Entity -> Me• Facts -> Name, Address, Phone,

Age, Ht, Wt, IQ, Eye, Hair• Facts can be related or unrelated• Name -> First, Last, MI• Address -> Str#, Street, City, State,

Zip

Data (cont.)

• Facts can be Unique to an entity (SSAN)• Facts can group people (City, Zip, Eye Color,

Income)• Facts give information, but must be processed• - Relate to an entity: SSAN->Individual• - Counted: Population of a state• - Ordered: Names in a telephone book• - Searched: Finding the people on a street

with children• - Segregated: Finding registered voters in a

district

Levels of Data

• Bit - 1's & 0's, Computers think in it• Character - One or more Bits• Field - One or more Characters, max size

important• Record - One or more Fields, Single field

data file is a list• File - One or more Records, (Draw flat file

example) (N, SS#, Ph)• (Note) Here is where most folks stop

Data Base - One or more files

- Why more than one file?• Different sources

List of names and address of students - List of Grades from each class- Merged to form ...Report Cards

• Info not achievable otherwise- List of names & Defaulted Loans- List of voter registrations- Result is recovery of money

Other Terms

• Data Banks: Groups of Data Bases

• DBMS: Data Base Management System

• Keys: The order that records are sorted/searched. Can be more than one– Primary Key: Should be unique to each record– Secondary Key(s)– Compound Keys: Eg. LName FName MI

Other Terms (cont.)

• Types of Data– Text: Sorts/Queries based on ASCII values of

characters

ASCII Table

Other Terms (cont.)

• Types of Data– Text: Sorts/Queries based on ASCII values of

characters– Number: Math functions can be performed on

these values– Date: Based on number of days since

12/31/1899• Days can be added or subtracted forming new

dates (Eg: 01/01/2006 + 7 = 01/08/2006)

• DBMS: Data Base Management System

The Relational Model– Data is stored on “Tables” of fixed-length

records– Portions of records called “Fields”– Similar fields in different files can be “Related”

• Individual records in different files can be linked based on data in “Related” fields being identical

– Very Flexible, Relations created “On-The-Fly”– Makes Cross-referencing possible

Tickets Issued Driver’s LicencesTic# Date DL# DL# Name Address

10101 1/1/97 60123 60123 Doe 151 Main

Other Terms (cont.)

• Queries– Method for selecting records that fit a criteria given– Eg: List all the records where the Last Name begins

with the letter S– In MS Access

• LName (assuming that’s what you named the field) in the Field Box

• “S*” in the Criteria Box• “*S*” for a sliding match (field contains the letter S)

– Queries Need three elements

A Table: where you are looking

A Criteria: what you want

A Report: how you want it to look