introduction to data bases. what is (are) data information? - no information is processed data data...
TRANSCRIPT
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Introduction to Data Bases
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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
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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
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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
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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
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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
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Other Terms (cont.)
• Types of Data– Text: Sorts/Queries based on ASCII values of
characters
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ASCII Table
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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
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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
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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
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A Table: where you are looking
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A Criteria: what you want
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A Report: how you want it to look