Data Integrity (Cambridge (CIE) A Level Computer Science): Flashcards
Exam code: 9618
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Define validation.
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Define validation.
Validation is an automated process where a computer checks if a user input is sensible and meets the program's requirements.
Define verification.
Verification is the act of checking data is accurate when it is being transferred or entered into a system.
What is the difference between validation and verification?
Validation checks that data is sensible and meets the program's requirements. Verification checks that data is accurate when it is transferred or entered.
Name the four verification methods.
The four verification methods are a parity check and a checksum (used on transfer), and double entry checking and visual checks (used on entry).
True or False?
Only one type of validation can be applied to a field.
False.
More than one type of validation can be used on a field. A password field could have a length, presence and type check on it.
Name the seven categories of validation.
The seven categories are a range check, format check, length check, presence check, existence check, limit check and check digit.
Define range check.
A range check ensures a number falls within a set range, for example that a percentage is between 0 and 100.
Define limit check.
A limit check checks that a value does not exceed a maximum limit, for example that no more than 5 items can be bought in a special offer.
What is the difference between a range check and a limit check?
A range check ensures a number falls within a set range, whereas a limit check only checks that a value does not exceed a maximum.
Define length check.
A length check checks the length of a string, for example confirming that a PIN is exactly 4 digits long.
Define presence check.
A presence check checks that data has been entered and that the field is not blank.
Define existence check.
An existence check checks that a referenced value exists in a database or list, for example that a student ID exists in the school records.
Define format check.
A format check ensures data is in the correct format, for example that an email address contains '@' and a domain such as '.com'.
What does a type check do?
A type check checks that the input is of the correct data type, for example that an age is entered as a whole number.
Define check digit.
A check digit is the last digit included in a code or sequence, used to detect errors in numeric data entry.
Name three types of error that a check digit can identify.
A check digit can identify incorrect digits entered, omitted or extra digits and phonetic errors.
Give two examples of where check digits are used.
Check digits are used in ISBN book numbers and barcodes.
How does a check digit show that an ISBN is valid?
A check digit algorithm is performed on the ISBN, and if the result is a whole number with no remainder then the ISBN is valid.
On a barcode, the digit is usually the check digit.
On a barcode, the final digit is usually the check digit.
Define parity check.
A parity check determines whether bits in a transmission have been corrupted.
What must the sender and receiver agree before transmission?
They must agree whether they are using odd or even parity.
How many bits of each transmitted byte are allocated as the parity bit?
One bit of every byte transmitted is allocated as the parity bit.
If even parity is used, what must be true of the byte?
There must be an even number of 1s in the byte, including the parity bit.
Even parity is agreed and the main bit string is 1 0 1 1 0 1 0.
What is the parity bit?
There are four 1s in the bit string, which is already even, so the parity bit is 0.
Odd parity is agreed and the main bit string is 1 1 0 1 0 0 1.
What is the parity bit?
There are four 1s in the bit string, which is even, so the parity bit must be 1 to make the total number of 1s odd (five).
True or False?
A parity check tells you where in the byte the error occurred.
False.
A parity check only shows that an error has occurred, not where it occurred.
What weakness do parity checks have?
Parity checks are quick and easy to implement, but they fail to detect bit swaps that leave the parity unchanged.
Bits can be flipped due to on a wire, or wirelessly due to weather or other signals.
Bits can be flipped due to interference on a wire, or wirelessly due to weather or other signals.
How does a parity block allow an error to be pinpointed?
A parity block totals the 1s horizontally and vertically, and by cross referencing the horizontal parity bits with the vertical parity byte the exact bit in error can be located.
Define parity byte.
A parity byte is a byte sent with the data that contains the parity bits from the vertical parity calculation.
Define checksum.
A checksum is a value used to determine if data has been corrupted or altered.
How does a checksum detect an error?
The receiving device re-calculates the checksum and compares it with the original. If the checksums do not match, an error is assumed.
Define double entry checking.
Double entry checking involves entering the data twice in separate input boxes and comparing them to ensure they match.
What is a visual check?
A visual check is where the user visually checks the data on the screen, and a message asks if the data is correct before proceeding.
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