Chapter 3 : Data - representation and structure Flashcards
Binary Coded Decimal
Similar to Binary
Eg. 7 in BCD is 0111
7 5 in BCD is 0111 0101
Binary
128 64 32 16 8 4 2 1
Octal
512 64 8 1
Hexadecimal
256 16 1
10 A
11 B
Binary Addition
0 + 0 = 0
0 + 1 = 0
1 + 0 = 0
1 + 1 = 0 ( carry one )
2’s Compliment
Can represent negative number
Eg. 1001 0001
= -128 + 16 + 1 = - 111
Sign and magnitude form
0 represents +
1 represents -
Eg. 1001 0001
= - ( 16 + 1 = 17 )
= - 17
Three main methods of character encoding
EBCDIC
ASCII
UNICODE
Define EBCDIC
It Was originally used on punch card computers by IBM
Define ASCII
All characters, punctuation and single numbers have their own assigned number
Define UNICODE
It contains characters such as mandarin characters, Thai characters and symbols.
Inputting methods
Form Design Keyboard Entry Voice Recognition Barcodes Optical Mark Recognition (OMR) Optical Character Recognition (OCR) Magnetic Ink Character Recognition (MICR) Touch screen Picture Capture Chip and PIN Sensor Remote data logging
Define Barcode
A series of black lines used to store a numerical value.
The thickness of each line represents a particular number.
The last number is always a check digit – printer and reader will be calculate then check against it
Define Optical Mark Recognition (OMR)
OMR is based on a pre defined form.
The form will have specific parts for someone to fill out by putting a pencil mark in the correct box.
A special reader will then read in this form and tell what was marked.
Eg. multiple choice exams and registers
Define Optical Character Recognition (OCR)
OCR converts printed media into digital form using a scanner
It produces a editable text file
The shapes of letters and numbers are compared to those stored in the memory and the computer will decide the order of the characters
Define Magnetic Ink Character Recognition (MICR)
MICR uses ink containing iron oxide and specific fonts so they can be read in by a specialist reader.
The cheque number and account number are written on the bottom of the cheque using magnetic ink.
This can then be very quickly read in by the reader so it can be quickly processed by the banks.
Define Sensor
Sensors can be found in mobile phones, cars, cookers and even games consoles.
A sensor will record some data from the physical environment
Examples of Sensor
Pressure sensor Accelerometers luminance sensor (light) Humidity sensor Infrared sensor
Forms of output
Graphs Reports Interactive Presentations Sound Video Images Animations
Validation and Verification
They are used to ensure any input provided by the user is as correct as it can be.
Purpose of Validation
It occur before data is committed to storage
Purpose of Verification
It occurs after data is committed to storage
Validation Checks
Format check - Ensure data conforms to a set a rules. Eg. email addresses must contain @
Existence - ensure data exists
Check digit - barcodes
Type check - ensure that the input is of the correct data type
Verification Checks
Proof reading - A human will read over the input to manually check.
