CIT PowerPoint presentation Group 4

Unit 1, Chapter 2 Basic Concept on Data DATA AND INFORMATION What is data? Data consists of all sorts of unorganised and incomprehensible facts in the form of numbers, characters, symbols, or graphics. What is information? Information is processed data which is meaningful and useful. DATA PROCESSING INFORMATION

DATA COLLECTION AND DATA PREPARATION 1) By interviews, Questionnaires and Forms 2) By Observations and Measurements 3) By Experiments –(–(–(–(1) Checking Data for Accuracy –(–(–(–(2) Structuring Data

DATA MANAGEMENT 1) Sources of Errors –(–(–(–(1) During Data Collection –(–(–(–(2) During Data Preparation –(–(–(–(3) During Data Input –(–(–(–(4) During Data Processing –(–(–(–(5) During Information Output “Garbage-in Garbage-out” situation

2) Data Control –(–(–(–(1) Data Verification Data items entered are outputted immediately or as a batch for checking against the original source, to find out if there are any mismatched items. Data items are typed into a computer by two different operators independently. A program is used to compare these two sets of data and detects any discrepancies. If data verification is extensively and properly used, then the data inputted should be identical with the original data.

(2) Data Validation Refers to the data inputted being acceptable and reasonable. To ensure data validity, a validation program is to check the data inputted. This is data validation. There are 5 Types of validation check! Type Check Range Check Length Check Reasonableness Check Check Digit

Type Check –T–T–T–Type check is used to check if the data types are correct. Data are usually divided into two types: numbers and characters. Range Check –R–R–R–Range check is used to ensure that data lie within a certain range.

Length Check –L–L–L–Length check is used to ensure the correct number of characters or digits in a data item. Reasonableness Check –R–R–R–Reasonableness check tries to ensure the reasonableness of data.

Check Digit –A–A–A–A check digit is an extra digit at the end of a code. It is used to ensure the correctness of the code. Example: Identity Card Number and the International Standard Book Number (ISBN) use check digits for validation purpose. The Check Digit of the Hong kong Identity Card Number The following is an illustraion on how to find the check digit of an identity card number, e.g. D308377(?), when the other digits are known. 1. Each digit has a weighting of 2,3,4,5,6,7,8 starting from right to left. D | | | | | | |___> 7*2 = 14 | | | | | |_____> 7*3 = 21 | | | | |______> 3*4 = 12 | | | |________> 8*5 = 40 | | |_________> 0*6 = 0 | |___________> 3*7 = 21 |_____________> 4*8 = 32

2. Calculate the “ weighted sum” of the digits of the given numbers. 7*2 = 14 7*3 = 21 3*4 = 12 8*5 = 40 0*6 = 0 3*7 = 21 +)4*8 = 32 The weighted sum = Divide the weighted sum by |140 12…...8(remainder)

4. Check Digit Check digit = 11 – remainder = 11 – 8 = 3 Note that if the remainder is 0, the check digit is 0. If the remainder is 1, the check digit is 10 and a letter “A” is used. Therefore, a valid identity card number is D308377(3). You will find that it is exactly “divisible” by 11, in the sense that D (3) | | | | | | | |_> 3*1 = 3 | | | | | | |___> 7*2 = 14 | | | | | |_____> 7*3 = 21 | | | | |______> 3*4 = 12 | | | |________> 8*5 = 40 | | |_________> 0*6 = 0 | |___________> 3*7 = 21 |_____________> 4*8 = 32 —————————————— 11 |

1) REPRESENTATION OF DATA INSIDE A COMPUTER A. Denary, Binary and Hexadecimal Number Systems –A–A–A–A number system is a system that represents numbers. For each number system, a number is composed of one or more digits. –T–T–T–The position of each digit in the number has its place value, and the digit value is represented by the product of the digit and its place –I–I–I–It must be noted that the place value of each digit is larger than that of the following digit by a factor. This factor is called the base, and is different for different number systems.

(1) Denary Number System We usually use the decimals or denary number system to represent a number. The denary number system uses ten digits to represent numbers: 0,1,2,3,4,5,6,7,8,9 and use 10 as its base. A number is formed by the combination of the digits. Example i.e = 4* * * *100

(2) Binary Number System In the binary number system, only digits 0 and 1 are used. It is base-2 number system. The binary numbers are constructed in the same way as the denary numbers except that the base is 2 instead of 10. Example The binary number in expanded form is: i.e = 1*23 + 1*22 + 1*21 + 1*20

(3) Hexadecimal Number System In the hexadecimal number system, the digits 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E and F are used. (A,B,C,D,E and F represent 10,11,12,13,14,15 respectively.) It is a base-16 number system. The hexadecimal number are constructed in the same way as the decimal numbers except that the base is 16 instead of 10. The hexadecimal number 2C3D16 in expanded form is: i.e. 2C3D16 = 2* *162 +3* *160

2) USING BINARY DIGITS TO REPRESENT DATA In a computer, data are represented by binary digits “0” and “1”. Each “0” or “1” is called a bit, short form for binary digits. Usually, eight bits are combined into a group called a byte to represent or encode one character. For example, the American Standard Code for Information Interchange (ASCII) is the most popular coding system for characters. It uses a byte as a code to represent each character.

END Ho Yat Pong 4B (10) Lai Yu Fai 4B (12) Leonardo Capocio Neto 4B (20)