Data Integrity
Data Integrity
Data stored on a computer should always be accurate, consistent and up to date.
during the data entry and data transmission stages
by malicious attacks on the data, for example caused by malware and hacking
by accidental data loss caused through hardware issues
Two of the methods used to ensure data integrity are validation and verification.
The accuracy (integrity) of data can be compromised
Two of the methods used to ensure are validation and verification
Validation
Validation is a method of checking if entered data is reasonable (and within a given criteria), but it cannot check if data is correct or accurate.
Validation methods:
type check
range check
format check
length check
presence check
existence check
limit check
consistency check
uniqueness check
Validation test type | Description | Example of data failing validation test | Example of data passing validation test |
|---|---|---|---|
type | checks whether non-numeric data has been input into a numeric-only field | typing sk.34 in a field which should contain the price of an item | typing 34.50 in a field which should contain the price of an item |
range | checks whether data entered is between a lower and an upper limit | typing in somebody’s age as –120 | typing in somebody’s age as 48 |
format | checks whether data has been entered in the agreed format | typing in the date as 12-12-20 where the format is dd/mm/yyyy | typing in the date as 12/12/2020 where the format is dd/mm/yyyy |
length | checks whether data has the required number of characters or numbers | typing in a telephone number as 012 345 678 when it should contain 11 digits | typing in a telephone number as 012 345 678 90 when it should contain 11 digits |
presence | checks to make sure a field is not left empty when it should contain data | please enter passport number:……………… | please enter passport number: AB 1234567 CD |
existence | checks if data in a file or a file name actually exists | data look up for car registration plate A123 BCD which does not exist | data look up for a file called books_in_stock which exists in a database |
limit check | Checks only one of the limits (such as the upper limit OR the lower limit) | typing in age as –25 where the data entered should not be negative | typing in somebody’s age as 72 where the upper limit is 140 |
consistency check | checks whether data in two or more fields match up correctly | typing in Mr in the title field and then choosing female in the sex field | typing in Ms in the title field and then choosing female in the sex field |
uniqueness check | checks that each entered value is unique | choosing the user name MAXIMUS222 in a social networking site but the user name already exists | choosing the website name Aristooo.com which is not already used |
Check digits
The check digit is an additional digit added to a number.
Check digit
The check digit is an additional digit added to a number.
An example of a check digit calculation is modulo-11.
The following algorithm is used to generate the check digit for a number with seven digits.
is a method of checking if entered data is reasonable (and within a given criteria), but it cannot check if data is correct or accurate
Which method checks whether data entered is between a lower and an upper limit
Which method checks whether data has the required number of characters or numbers
Which method checks to make sure a field is not left empty when it should contain data
Verification
Verification is a way of preventing errors when data is entered manually (using a keyboard, for example) or when data is transferred from one computer to another.
Double entry
Data is entered twice, using two different people, and then compared.
Visual check
Entered data is compared with the original document.
Verification during data transfer
When data is transferred electronically from one device to another, there is always the possibility of data corruption or even data loss.
A number of ways exist to minimise this risk.
Checksums
A checksum is a method to check if data has been changed or corrupted following data transmission.
Data is sent in blocks and an additional value, the checksum, is sent at the end of the block of data.
Parity check
A parity check is another method to check whether data has been changed or corrupted following transmission from one device or medium to another.
A byte of data, for example, is allocated a parity bit. This is allocated before transmission.
Systems that use even parity have an even number of 1-bits; systems that use odd parity have an odd number of 1-bits.
Naturally, any of the bits in the above example could have been changed leading to a transmission error.
Therefore, even though an error has been flagged, it is impossible to know exactly which bit is in error.
Parity blocks is a block of data is sent and the number of 1-bits are totalled horizontally and vertically.
parity bit | bit 2 | bit 3 | bit 4 | bit 5 | bit 6 | bit 7 | bit 8 | |
|---|---|---|---|---|---|---|---|---|
byte 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 | 0 |
byte 2 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 1 |
byte 3 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 0 |
byte 4 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
byte 5 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 1 |
byte 6 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
byte 7 | 1 | 0 | 1 | 0 | 1 | 1 | 1 | 1 |
byte 8 | 0 | 0 | 0 | 1 | 1 | 0 | 1 | 0 |
byte 9 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 |
parity byte | 1 | 1 | 0 | 1 | 0 | 0 | 0 | 1 |
A careful study of the table shows that
byte 8 (row 8) has incorrect parity (there are three 1-bits)
bit 5 (column 5) also has incorrect parity (there are five 1-bits).
Automatic repeat request (ARQ)
Automatic repeat request (ARQ) is another method to check data following data transmission.
ARQ uses acknowledgement (a message sent to the receiver indicating that data has been received correctly) and timeout (the time interval allowed to elapse before an acknowledgement is received).
When the receiving device detects an error following data transmission, it asks for the data packet to be resent.
If no error is detected, a positive acknowledgement is sent to the sender.
The sending device will re-send the data package if it receives a request to re-send the data, or a timeout has occurred.
The whole process is continuous until the data packet received is correct or until the ARQ time limit (timeout) is reached.
is a way of preventing errors when data is entered manually (using a keyboard, for example) or when data is transferred from one computer to another
Verification normally includes:
Data is sent in blocks and an additional value, the , is sent at the end of the block of data.
A refers to an error detection method where an extra bit, or a parity bit, is added to each data unit
(ARQ) is another method to check data following data transmission.
Find the parity bits for each of the following bytes:
1101101 even parity used
1110100 odd parity used
ARQ uses (a message sent to the receiver indicating that data has been received correctly) and (the time interval allowed to elapse before an acknowledgement is received).