Contents

1. We live in an "Information Age"
2. Storing Information
3. Internally Indistinguishable
4. A FILE: Works Like a File Folder
5. Free-form storage
6. RECORD: Getting More Organized
7. FIELDS: Subdividing Records
8. Finding Information
9. Identifying Records: KEY FIELDS

About this document...

1. We Live in an "Information Age"

• Knowledge is power
• Computers store most of our information
• ...How?

2. Storing Information:

• Computers were built to hold numbers

Stored as on/off switches
• One on/off switch: a bit

binary digit 0 or 1
• Larger numbers: combinations of bits based on powers of 2 "binary" Examples:

Base two     0 1 10 100 1000 1111
is base ten  0 1  2   4    8   15
• Can be used in calculations
• Characters stored as numeric codes

Characters are:
• Letters A-Z, a-z
• Digits 0-9

Digits can not be used in calculations!
• Special symbols and punctuation:

~!@#$%^&*()_-+=|\/{}[]:;"`'<>?,.
• Codes: arbitrary assignment
• ASCII on all small, many large

American Standard Code for Information Interchange
pronounced ASK-ee
A = 65, B = 66, C = 67 ...
• EBCDIC on many large computers

Extended Binary Coded Decimal Interchange Code
pronounced EB-see-dick
A = 193, B = 194, C = 195 ...
• Characters stored in an 8-bit unit

This unit is called a byte.
• Other information is also stored using numbers, such as:
• Pictures: numbers represent color and brightness, or coefficients of equations
• Sounds: numbers represent pitch and amplitude, digitized sound waves, or equations
• Computers also store instructions

These work like phone numbers...
Each number sets electronic switches to make proper connections
Format depends on type of computer.

3. Internally Indistinguishable

4. A FILE: Works Like a File Folder.

• Named space
• To store related information
• Can be long or short
• Can have: characters, numbers, programs, or other data

5. Free-form storage

A. Lines can be as long as desired

B. All one type: character data

C. How do you find something?
...look through everything!

6. RECORD: Getting More Organized

A. Originally a punched card

B. Record sizes:

• Fixed length records

Pre-determined length for rapid sorting.
Like alphabetizing index cards vs. papers of different sizes.
• Variable length records

Can be any number of characters long: like spreadsheet cell
can contain small or large label, number, or formula

7. FIELDS: Subdividing Records

A. Sometimes fields are fixed length, sometimes variable;

B. Fields usually either character or numeric.

8. Finding Information

• Sequential = one-after-another

Start with first record, check until desired record found
Fine for some kinds of batch job
Example: payroll
No good for interactive work
• Random = use rapid search pattern

Find any record as fast as any other
Necessary for some kinds of batch work
...and for all interactive work
   Example: airline reservations
Indexing: works like a book index
Other methods: Hashing, ISAM, VSAM, etc.

• Ascending order

Going up: small to large, A, B, C... or 1, 2, 3...
• Descending order:

Going down: large to small, Z, Y, X... or 9, 8, 7...

9. Identifying Records: KEY FIELDS

• Key fields determine sorting order:

Name, zip code ...
• Keys may also provide uniqueness

Unique = one-of-a-kind
Required for some kinds of system
Example: Social Security number.

Audience:

Objectives

• The two primary data storage types: character and numeric, and the fact the instructions are also stored as data;
• The use of ASCII and EBCDIC as character codes;
• Organized storage as compared with free-form storage;
• How word processors and spreadsheets store information;
• Fixed record format as compared with variable record format;
• Usage of the terms "file," "record," and "field;"
• Data-finding methods, including sequential search and indexed search;
• The role of key fields in establishing sort order and uniqueness;

About this document...

Module G15c: Data Management Principles

Author:

Laurence J. Krieg

Institution:

Department of Computer Information Systems, Washtenaw Community College

Revision Date:

Original 9 March 1988

Revised 7 March 1991
HTML version 14 October 1996