1. Verification & Validation
F451 AS Computing

2. X Why check data? It’s useless if inaccurate. Also, wrong data:
Can be annoying
Can cost a fortune
Can be dangerous X
£45.67
£297.99

4. How do data errors happen?
Speeling Mitsakes
Typing the the same thing twice
Leaving an important field blank
Typing wrong numbers – 19/38/05

5. How can you check data? VALIDATION …Is it valid or allowed?
Computers use software to check data
2 types of data check:
VALIDATION
…Is it valid or allowed?
VERIFICATION
…Is it the same?

6. Verification Data entered twice, then compared
What common data is verified?
Passwords

7. Data Entry - Verification
Where data is entered into a system often 2 data entry operators will enter the same data and the data is compared to verify it.
This ensure data is correctly inputted and spots human errors.

8. Validation Range checks Format Check Type/Character Checks
Ensures data entered complies with allowable data
Many different types of validation include:
Range checks
Format Check
Type/Character Checks
Presence Checks
Length Check
Lookup/Existence Check
Check Digits

9. Class Activity - Are these dates possible? 
19/12/78
12/19/90
3rd June 1999
30th Feb 2003
31st September 2001
29th Feb 2004
01/01/2003 ?    

10. Range check and Type check
Range checks
i.e. is between 1 and 100
Type checks
i.e is numeric and not text
Please type in your age:
6000
Please type in your age:
old

11. Length & Presence checks
Length check
Checks to see if input data contains certain numbers of characters
Presence check
Ensures values have actually been entered in to the data store
Certain key fields are compulsory
Please type in your screen name (min 4 characters)
JON
Please type in your age:

12. Coding data Human data input error is common
Coded values can prevent this
S, M, L can represent small, medium and large
Head Size
Small - S
Medium - M
Large - L F

13. Look-up Check
Sometimes, a list box or combo box displays allowable items, so input is selected from a list

14. Existence Check

15. Class Exam Question Chan D4n 132 Accounts 572 Wendy 123 Training 467
Surname
Forename
Dept Number
Dept Name
Ext Number
Chan
D4n
132
Accounts
572
Wendy
123
Training
467
Jones
Sarah
121
468
Dan
Patel
Paul
573
The records in this file have been input with the validation checking turned off. Referring to the records above, state four problems that have occurred. (4)
(b) Name and describe three different validation checks that would have prevented these problems. (6)

16. Backups Making copy of important files on a portable medium
Store the media away from originals
If the original file is corrupted it can be replaced quickly
ALWAYS BACKUP YOUR FILES!

17. Backup Strategy Frequency of Backup – Eg Weekly
Medium used – eg Memory Stick
Where the medium is stored? On or off site.
Full Backup
Copies every file fully
Incremental Backup
Only copies files that have been altered since last backup

18. Back-up & Disaster Planning
Organisations must plan for computer failure
Large companies have comprehensive plans
Back up and running within days of major catastrophe
Smaller companies can survive with less sophisticated systems
Back up system is still vital

19. Back-up & Disaster Recovery
The following factors need to be considered when establishing a backup strategy:
The frequency of backup
The medium of storage
Location of the media
Number of generations to keep
The use of full or incremental backups
Trained staff to implement strategy
Effective recovery procedure.
Process should be documented.

20. Back Up Hardware
Zip Disk
Tape Cartridge
DVD-Rom/CD-Rom
RAID

21. Archiving Not the same as backup Storing old/unused data
Taking it from server/mainframe
Transferring onto storage medium
Stored “off-line”
Unlikely to be used again, but still available

22. Archiving
Storing data files on a portable storage device and keep them in a secure location.
Data is stored offline.
It can be recovered in an emergency/disaster recovery situation.

23. Practical Exercise Create 3 types of validation checks within Delphi
Range check
Length check
Password verification