4. Organisation and structure of data

Question 1

What is overflow?

Answer 1

When a value is too large to store with the number of bits available. In binary addition, this happens when there is a carry on the MSB.

Question 2

What should be considered when designing a file?

Answer 2

• field name
• example data
• data type
• validation check

Question 3

What is the difference between validation and verification?

Answer 3

Validation is checking that data is acceptable before it is entered, and verification is checking data is correct after it has been entered.

Question 4

Describe some validation checks

Answer 4

• range check: check data is within a certain range
• type check: check data is a certain data type
• format check: checks data is entered in a certain way
• presence check: checks data has been entered and not left blank
• lookup table: a table of acceptable entries (could be a list)
• length check: checks the length of the input

Question 5

Describe some verification checks

Answer 5

• double entry: typing in data twice to make sure there were no spelling errors the first time
• proofreading: checking two copies of data to ensure they are exactly the same
• check digit: calculated on barcodes to ensure the rest of the numbers are correct, similar to a checksum in a data packet