This section is about data entry errors how they are distinguished and how we can recover from them. For further reading read your book and click here !
Data entry
Data entry errors typically occur in data processing systems such as billing systems, stock control, banking and payroll. Errors can be made when entering data at the keyboard or when reading data input from other devices.
Typical accidental errors are transposition and transcription . A transposition error occurs when digits are entered the wrong way round, such errors are very common : eg entering 316 instead of 3.6.1. A transcription error occurs when one digit is written for another: eg 3.8.1 instead of 3.6.1.
Deliberate errors will be the result of a security breach or fraud - a student may break into the examination database and change their grade or a bank employee may credit $450 of a $500 deposit but keep $50 for themselves. Usually, fraudsters are slightly more sophisticated than this.
Detecting errors
There are methods of checking for both these types of error. It is important to distinguish betweenvalidation and verification .
Verification means making sure that the data on the source documents is exactly the same as that input to the computer system.
Validation means attempting to make sure that the data input into the system makes sense.
Verification
There are two main methods in common use; Visual verification (or proof-reading) which means checking data on screen to see if it is the same as on the source document.
Double entry verification which involves having the data from the source document entered twice as a check. Typically the application will lock the keyboard and give an audible warning so that the data entry person can check carefully.
One of these methods is more reliable than the other.
Validation
Data entered into the computer can be unreasonable, a data entry person in a medical clinic can easily mistype a person's weight, say or the number of cigarettes they smoke per day. This type of error is not caught by verification since the data may have been written down wrongly in the first place.
Validation also checks for incomplete or inaccurate data. The main types of validation checks arerange checks, type checks and format checks.
Range checks see if numeric data is in the correct range (eg a percentage mark needs to be between 0 and 100).
Type checks check that data is of appropriate type (integer, real or character for example).
Format checks are used to see if the data has the correct length or other internal structure (eg ddmmyyyy).
Find out more about these types of check - see your book or a good website.
Data entry
Data entry errors typically occur in data processing systems such as billing systems, stock control, banking and payroll. Errors can be made when entering data at the keyboard or when reading data input from other devices.
Typical accidental errors are transposition and transcription . A transposition error occurs when digits are entered the wrong way round, such errors are very common : eg entering 316 instead of 3.6.1. A transcription error occurs when one digit is written for another: eg 3.8.1 instead of 3.6.1.
Deliberate errors will be the result of a security breach or fraud - a student may break into the examination database and change their grade or a bank employee may credit $450 of a $500 deposit but keep $50 for themselves. Usually, fraudsters are slightly more sophisticated than this.
Detecting errors
There are methods of checking for both these types of error. It is important to distinguish betweenvalidation and verification .
Verification means making sure that the data on the source documents is exactly the same as that input to the computer system.
Validation means attempting to make sure that the data input into the system makes sense.
Verification
There are two main methods in common use; Visual verification (or proof-reading) which means checking data on screen to see if it is the same as on the source document.
Double entry verification which involves having the data from the source document entered twice as a check. Typically the application will lock the keyboard and give an audible warning so that the data entry person can check carefully.
One of these methods is more reliable than the other.
Validation
Data entered into the computer can be unreasonable, a data entry person in a medical clinic can easily mistype a person's weight, say or the number of cigarettes they smoke per day. This type of error is not caught by verification since the data may have been written down wrongly in the first place.
Validation also checks for incomplete or inaccurate data. The main types of validation checks arerange checks, type checks and format checks.
Range checks see if numeric data is in the correct range (eg a percentage mark needs to be between 0 and 100).
Type checks check that data is of appropriate type (integer, real or character for example).
Format checks are used to see if the data has the correct length or other internal structure (eg ddmmyyyy).
Find out more about these types of check - see your book or a good website.