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2 - Practical Problem Solving & Programming / Validation
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Validation and Verification
Validation and Verification are both used to ensure that data entered into a computer system is correct and reasonable. The use of both Validation and verification is vital for the smooth running of computer systems.
Validation
Validation is a process that checks that data is reasonable before it is accepted by a computer system. Validation is automated meaning that a well designed algorithm should successfully decide whether or not data is acceptable.
There are a number of different Validation checks that can be performed on data. These include:
- Range Checks
- Presence Checks
- Format Checks
- Type Checks
- Character Checks
- Check Digits
Each of these checks are explained in more detail below:
Range Checks
A range check is used to ensure that numbers are only accepted into a program if it falls within a certain acceptable range.
Example - If a program asks for somebodies age then you might limit entries to be between 13 and 100. This would potentially prevent people under the age of 13 from signing up and it would also prevent people giving an unrealistic age e.g. 250 years old.
Pseudo code for a validation check like this may look like:
Age = 0
OUTPUT "Please enter your age"
Age = INPUT()
WHILE Age < 13 OR Age > 100 DO
IF Age < 13 THEN
OUTPUT "Sorry, you are too young"
ELSE IF Age > 100 DO
OUTPUT "Sorry, Age entered is not realistic - it is too high"
END IF
OUTPUT "Please re-enter your age"
Age = INPUT()
END WHILE
You can test this out yourself using the Python Trinket below...
Example - If a program asks for somebodies age then you might limit entries to be between 13 and 100. This would potentially prevent people under the age of 13 from signing up and it would also prevent people giving an unrealistic age e.g. 250 years old.
Pseudo code for a validation check like this may look like:
Age = 0
OUTPUT "Please enter your age"
Age = INPUT()
WHILE Age < 13 OR Age > 100 DO
IF Age < 13 THEN
OUTPUT "Sorry, you are too young"
ELSE IF Age > 100 DO
OUTPUT "Sorry, Age entered is not realistic - it is too high"
END IF
OUTPUT "Please re-enter your age"
Age = INPUT()
END WHILE
You can test this out yourself using the Python Trinket below...
The above code works do validate the age through the use of a WHILE loop. The user will not be allowed to progress to the next part of the program until the age lies between 13 and 100 (A REPEAT UNTIL loop could also be used). Of course this program is not perfect as a 10 year old would simply get a chance to enter their age again and lie about it, however the code should illustrate the practical implementation of a range check.
Presence check
A Presence check is used to ensure that some data has been entered. This is used where you cannot allow the user to progress until they provide you with information e.g. a user cannot sign up to a service if they have left the e-mail field empty.
Example - An internet blog has the ability to post comments. You do not need to create an account, however before the post is published you do need to enter your name. In this case there are no rules about how long your name should be, or even that it has to be realistic. The only rule is that you have to enter a name.
Pseudo code for a validation check like this may look like:
Name = ""
OUTPUT "Please enter your name so that we can post your comment"
Name = INPUT()
WHILE Name = "" DO
OUTPUT "Sorry, You must enter a name before your post can be published"
Name = INPUT()
END WHILE
OUTPUT "Thank you " + Name + " Your comment has been published"
You can test this out yourself using the Python Trinket below. Try testing what will happen when you enter nothing vs when you enter a name.
Example - An internet blog has the ability to post comments. You do not need to create an account, however before the post is published you do need to enter your name. In this case there are no rules about how long your name should be, or even that it has to be realistic. The only rule is that you have to enter a name.
Pseudo code for a validation check like this may look like:
Name = ""
OUTPUT "Please enter your name so that we can post your comment"
Name = INPUT()
WHILE Name = "" DO
OUTPUT "Sorry, You must enter a name before your post can be published"
Name = INPUT()
END WHILE
OUTPUT "Thank you " + Name + " Your comment has been published"
You can test this out yourself using the Python Trinket below. Try testing what will happen when you enter nothing vs when you enter a name.
The above code works to validate the presence of a name through the use of a WHILE loop. The user will not be allowed to progress to the next part of the program until the Name variable contains data. Whilst the Name variable remains empty the user will be asked to enter a name. (A REPEAT UNTIL loop could also be used).
Format Check
A format check is used to ensure that data entered matches a desired pattern. e.g. if a user is required to enter an email address then it should follow a set pattern of "XXXXX" + @ + "XXXXX" + "." + "XXX" This would allow an email address such as "example@gmail.com" to be accepted.
Another example of a format check would be to check that an ID number has been entered in the correct format. Lets imaginge that in our program an ID number must begin with the organisations initials ISS and must end with 4 numbers e.g ISS1432.
Pseudo code for a validation check like this may look like:
OUTPUT "Please enter an ID number e.g. ISS1111"
Accepted = False
While Accepted = False Do:
IDNo = INPUT()
First = IDNo[0,1,2]
Last = IDNo[3,4,5,6]
Length = Len(IDNo)
IF Length =7 THEN AND First = "ISS" AND (Last >=0000 AND Last <=9999):
Accepted = TRUE
ELSE:
OUTPUT "ID Not acceptable - Please try again"
END IF
END WHILE
OUTPUT "Acceptable ID no entered.
You can test this out yourself using the Python Trinket below. Try testing what will happen when you enter a valid or invalid ID Number. This example is case sensitive - the ISS must be capitol latters to be accepted.
Another example of a format check would be to check that an ID number has been entered in the correct format. Lets imaginge that in our program an ID number must begin with the organisations initials ISS and must end with 4 numbers e.g ISS1432.
Pseudo code for a validation check like this may look like:
OUTPUT "Please enter an ID number e.g. ISS1111"
Accepted = False
While Accepted = False Do:
IDNo = INPUT()
First = IDNo[0,1,2]
Last = IDNo[3,4,5,6]
Length = Len(IDNo)
IF Length =7 THEN AND First = "ISS" AND (Last >=0000 AND Last <=9999):
Accepted = TRUE
ELSE:
OUTPUT "ID Not acceptable - Please try again"
END IF
END WHILE
OUTPUT "Acceptable ID no entered.
You can test this out yourself using the Python Trinket below. Try testing what will happen when you enter a valid or invalid ID Number. This example is case sensitive - the ISS must be capitol latters to be accepted.
The above code works but it could be improved. Currently it does not let the user know why the code that they entered was incorrect. It would be possible to break down the IF statement into nested IFs so that the user could be provided with helpful prompts e.g. "Your ID number does not start with "ISS""
Type Check
A Type check is used to ensure that the correct data type has been entered. This means that if you are requesting an integer then the program will only accept an integer, a string or any other data type would be rejected.
An example scenario for this would be a program that asks the user to enter their age. This input should be a whole number and therefor an integer. If any other type of data is entered then it should be rejected and the user should be given the chance to try again.
Pseudo code for a validation check like this may look like:
OUTPUT "Please enter your age"
Accepted = False
While Accepted = False Do:
Age = INPUT()
IF Age.isdigit():
Accepted = TRUE
ELSE:
OUTPUT "Age Not acceptable - Must be a whole number"
END IF
END WHILE
OUTPUT "Acceptable Age entered.
You can test this out yourself using the Python Trinket below. Try testing what will happen when you enter a string or a decimal number.
An example scenario for this would be a program that asks the user to enter their age. This input should be a whole number and therefor an integer. If any other type of data is entered then it should be rejected and the user should be given the chance to try again.
Pseudo code for a validation check like this may look like:
OUTPUT "Please enter your age"
Accepted = False
While Accepted = False Do:
Age = INPUT()
IF Age.isdigit():
Accepted = TRUE
ELSE:
OUTPUT "Age Not acceptable - Must be a whole number"
END IF
END WHILE
OUTPUT "Acceptable Age entered.
You can test this out yourself using the Python Trinket below. Try testing what will happen when you enter a string or a decimal number.
In the real world this solution would need to be validated further. You might want to add a range check to it to ensure that a realistic age is entered e.g. a max age of 100.
Character Check
A Type check is used to ensure that an entered string does not contain any unacceptable characters.
An example scenario might be that a user needs to choose a username. The username cannot contain the ! or @ symbol as they are reserved for admin usernames.
Pseudo code for a validation check like this may look like:
OUTPUT "Please choose a username"
Accepted = False
Find = False
While Accepted = False Do:
Username = INPUT()
length = len(Username)
FOR x = 0 to Length DO:
IF Username(x) = "!" OR Username(x) = "@"
Find = True
END IF
END FOR
IF Find = True THEN:
Accepted = False
Find = False
OUTPUT "Unacceptable Username, cannot contain ! or @ symbols"
Else:
Accepted = True
END IF
END WHILE
OUTPUT "Acceptable username entered"
You can test this out yourself using the Python Trinket below. Try testing what will happen when you enter a username that contains the symbols ! or @ then test what happens when you enter an acceptable username.
An example scenario might be that a user needs to choose a username. The username cannot contain the ! or @ symbol as they are reserved for admin usernames.
Pseudo code for a validation check like this may look like:
OUTPUT "Please choose a username"
Accepted = False
Find = False
While Accepted = False Do:
Username = INPUT()
length = len(Username)
FOR x = 0 to Length DO:
IF Username(x) = "!" OR Username(x) = "@"
Find = True
END IF
END FOR
IF Find = True THEN:
Accepted = False
Find = False
OUTPUT "Unacceptable Username, cannot contain ! or @ symbols"
Else:
Accepted = True
END IF
END WHILE
OUTPUT "Acceptable username entered"
You can test this out yourself using the Python Trinket below. Try testing what will happen when you enter a username that contains the symbols ! or @ then test what happens when you enter an acceptable username.
