Slides in this set
4 Checking data
Data stored on a computer is only useful as long as
it is correct and up-to-date.
it is important to check data when it is entered to
make sure that it is both sensible and correct.
If data is not checked before it is processed any
errors could cause the final output to be nonsense.
There are two methods that can be used to check
data when it is input.
These are called verification and validation.…read more
Verification is checking to make sure that data has
been entered correctly.
Verification is often carried out by getting two users to
enter the same set of data at different computers.
Once both users have entered the data the two sets of
data are compared to check that they match up.
Any data that does not match up is rejected.
Verification can also be carried out by software which
might, for example, ask for the same data to be entered
twice. If both entries don't match up the data is
Validation checks are carried out by software to make
sure that data which has been entered is allowable and
Data that is not sensible or allowed is rejected by the
There are many different types of validation check that
software can make on data.
We will now look at some of these in more detail.…read more
Range checks are used to check that data is within a
certain range of numbers or a specific set of values.
For example if the examination marks for a group of
students was being input a range check could be used to
make sure that each mark was greater than or equal to
zero and less than or equal to the maximum possible
Type checks are used to check that the correct type of
data has been entered in a field.
For example if numeric data is being input a type check
could be used to make sure that text data isn't entered
Length checks are used to check that input data
contains a certain number of characters.
For example if a value in a certain field had to contain
five digits and only four digits were input, an error
message would be given to the user.…read more
A presence check is used to make sure that a value has
actually been entered in a field.
In some database files entering data in certain fields can
be optional. Other fields, such as key fields for example,
are compulsory and must have values entered in them.
A presence check makes sure that data is present in a
field where it is compulsory that a value is needed.…read more