Integrity of Data for O & A Level Computer Science by Inqilab Patel

Описание: Integrity of data:
o Sensibility of data
o Correctness of data.
• at the time of entry
• at the time of transmission
Validation and Verification
Validation and verification are two ways to check that the data entered into a computer is correct. Data entered incorrectly is of little use.
Data verification
Verification is performed to ensure that the data entered or transmitted exactly matches the original source.
Verification means checking the input data with the original data to make sure that there have been no transcription errors (transcription means copying the data). The standard way to do this is to input the data twice to the computer system. The computer then checks the two data values (which should be the same) and, if they are different, the computer knows that one of the inputs is wrong. E.g. entering password twice during sig-up. Verification methods include:
Double entry
Double Entry
Parity check
Screen/visual check
Checksum.
ARQ
Echo Check
Validation is an automatic computer check to ensure that the data entered is sensible and reasonable. It does not check the accuracy of data.
For example, a secondary school student is likely to be aged between 11 and 16. The computer can be programmed only to accept numbers between 11 and 16. This is a range check.
However, this does not guarantee that the number typed in is correct. For example, a student's age might be 14, but if 11 are entered it will be valid but incorrect.
A validation check is a rule that is built into a database to check that the data entered is:
• Sensible
• Reasonable
• Within acceptable boundaries
• Complete
Validation does NOT mean that the data is actually correct, that requires verification.
There are a number of different validation rules that can be used in a database:

Summary of validation
Validation type How it works Example usage
Range check Checks that a value falls within the specified range Number of hours worked must be less than 50 and more than 0
Limit Check Similar to Range Check but the rule involves only one limit.
Length check Checks the data isn't too short or too long. Values must be a specific length. A password which needs to be six letters long
Presence check Checks that data has been entered into a field In most databases a key field cannot be left blank
Type Check Checks that the data entered is of a given data type, Number of brothers or sisters would be an integer (whole number).
Character Check Checks that when a string of characters is entered it does not contain any invalid characters or symbols, A name would not contain characters such as %, and a telephone number would only contain digits or (,), and + .
Format Check: Checks the data is in the right format. Values must conform to a specific pattern, for example, two letters followed by six digits followed by a single letter A candidate number, PK-500-1234 or National Insurance number is in the form LL 99 99 99 L where L is any letter and 9 is any number. for Date dd/mm/yyyy or mm/dd/yyyy
Check digit The last one in a code are used to check the other digits are correct Bar code readers in supermarkets use check digits
length check – e.g. only 30 characters in name field
character check – e.g. name doesn’t contain numeric chars
range check – e.g. day of month in date is between 1 and 31
format check – e.g. date in the form dd/mm/yyyy
check digit – e.g. end digit on bar code to check if it is valid
type check – e.g. integer, real