1. 2. Data Formats
Chapt. 3

2. Introduction Examples Real World Data Computer Data Input device
Dear Mom:
Keyboard …
Digital camera … pp

3. Format must be appropriate
The internal representation must be appropriate for the type of processing to take place (e.g., text, images, sound)

4. Rules/Conventions Proprietary formats Standards
Unique to a product or company
E.g., Microsoft Word, Corel Word Perfect, IBM Lotus Notes
Standards
Evolve two ways:
Proprietary formats become de facto standards (e.g., Adobe PostScript, Apple Quick Time)
Committee is struck to solve a problem (Motion Pictures Experts Group, MPEG) pp

5. Standards Organizations
ISO – International Standards Organization
CSA – Canadian Standards Association
ANSI – American National Standards Institute
IEEE – Institute for Electrical and Electronics Engineers
Etc.

6. Examples of Standards Type of Data Standards Alphanumeric
ASCII, EBCDIC, Unicode
Image
JPEG, GIF, PCX, TIFF
Motion picture
MPEG-2, Quick Time
Sound
Sound Blaster, WAV, AU
Outline graphics/fonts
PostScript, TrueType, PDF

7. Why Standards? Standard are “arbitrary” They exist because they are
Convenient
Efficient
Flexible
Appropriate
Etc.

8. Alphanumeric Data
Problem: Distinguishing between the number 123 (one hundred and twenty-three) and the characters “123” (one, two, three)
Four standards for representing letters (alpha) and numbers
BCD – Binary-coded decimal
ASCII – American standard code for information interchange
EBCDIC – Extended binary-coded decimal interchange code
Unicode pp

9. Standard Alphanumeric Formats
BCD
ASCII
EBCDIC
Unicode
Next 2 slides

10. Binary-Coded Decimal (BCD)
Four bits per digit
Digit
Bit pattern
0000 1
0001 2
0010 3
0011 4
0100 5
0101 6
0110 7
0111 8
1000 9
1001
Note: the following bit patterns are not used:

11. Example
= ? (in BCD)

12. Standard Alphanumeric Formats
BCD
ASCII
EBCDIC
Unicode
Next 22 slides

13. The Problem
Representing text strings, such as “Hello, world”, in a computer

14. Codes and Characters Each character is coded as a byte
Most common coding system is ASCII (Pronounced ass-key)
ASCII = American National Standard Code for Information Interchange
Defined in ANSI document X

15. ASCII Features 7-bit code 8th bit is unused (or used for a parity bit)
27 = 128 codes
Two general types of codes:
95 are “Graphic” codes (displayable on a console)
33 are “Control” codes (control features of the console or communications channel)

16. ASCII Chart

18. Most significant bit
Least significant bit

19. e.g., ‘a’ =

20. 95 Graphic codes

21. 33 Control codes

22. Alphabetic codes

23. Numeric codes

24. Punctuation, etc.

25. “Hello, world” Example = Binary 01001000 01100101 01101100 01101111
Hexadecimal 48 65 6C 6F 2C 20 77 67 72 64
Decimal
101
108
111 44 32
119
103
114
100 H e l o , w r d

26. Common Control Codes CR 0D carriage return LF 0A line feed
HT 09 horizontal tab
DEL 7F delete
NULL 00 null
Hexadecimal code

28. Terminology Learn the names of the special symbols [ ] brackets
{ } braces
( ) parentheses
@ commercial ‘at’ sign
& ampersand
~ tilde

30. Escape Sequences Extend the capability of the ASCII code set
For controlling terminals and formatting output
Defined by ANSI in documents X and X
The escape code is ESC = 1B16
An escape sequence begins with two codes: ESC [
1B16
5B16

31. Examples
Erase display: ESC [ 2 J
Erase line: ESC [ K

32. Standard Alphanumeric Formats
BCD
ASCII
EBCDIC
Unicode
Next 1 slides

33. EBCDIC Extended BCD Interchange Code (pronounced ebb’-se-dick)
8-bit code
Developed by IBM
Rarely used today
IBM mainframes only

34. Standard Alphanumeric Formats
BCD
ASCII
EBCDIC
Unicode
Next 2 slides

35. Unicode 16-bit standard Developed by a consortia
Intended to supercede older 7- and 8-bit codes

36. Unicode Version 2.1 1998 Improves on version 2.0
Includes the Euro sign (20AC16 = )
From the standard:
…contains 38,887 distinct coded characters derived from the supported scripts. These characters cover the principal written languages of the Americas, Europe, the Middle East, Africa, India, Asia, and Pacifica.

37. Keyboard Input Key (“scan”) codes are converted to ASCII
ASCII code sent to host computer
Received by the host as a “stream” of data
Stored in buffer
Processed
Etc.
pp. 69

38. Shift Key inhibits bit 5 in the ASCII code Key(s) ASCII code
Character a A a
Shift a

39. Control Key inhibits bits 5 & 6 in the ASCII code Key(s) ASCII code
Character c
ETX c
Ctrl c
Control code

40. Other Input OCR – optical character recognition Bar code readers
Voice/audio input
Punched cards
Images / objects
Pointing devices pp

41. OCR
Hello, world
Optical scan …
Page of text
Computer file

42. Other Input OCR – optical character recognition Bar code readers
Voice/audio input
Punched cards
Images / objects
Pointing devices pp

43. Bar Codes
An automatic identification (Auto ID) technology that streamlines identification and data collection
See

44. Other Input OCR – optical character recognition Bar code readers
Voice/audio input
Punched cards
Images / objects
Pointing devices pp

45. Voice/audio Input Input device: microphone
Audio input is “digitized” and stored
Processed in two ways
As is (no recognition)
Recognized and converted to alphanumeric data (ASCII)
Digitize …

46. Other Input OCR – optical character recognition Bar code readers
Voice/audio input
Punched cards
Images / objects
Pointing devices pp

47. Punched Cards Invented by Herman Hollerith (founder of IBM)
Each card holds 80 characters

48. Other Input OCR – optical character recognition Bar code readers
Voice/audio input
Punched cards
Images / objects
Pointing devices pp

49. Images
Typically images are pictures that are optically scanned and saved as a “bit map” or in some other format
Many formats
gif, jpeg, …

50. Typical “Save As” Dialog

51. Objects Images made of geometrically definable shapes
Offer efficiency, flexibility, small size, etc.

52. Other Input OCR – optical character recognition Bar code readers
Voice/audio input
Punched cards
Images / objects
Pointing devices pp

53. Pointing Devices
Originally used for specifying coordinates (x, y) for graphical input
Today used as general purpose device for “graphical user interfaces” (GUIs)

54. Thank you