Verification & Validation F451 AS Computing

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

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

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

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

Validation 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

Class Activity - Are these dates possible? 1. 19/12/ /19/ rd June th Feb st September th Feb /01/2003   ?

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 old

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 age: Please type in your screen name (min 4 characters) JON

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

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

Existence Check

Class Exam Question SurnameForename Dept Number Dept Name Ext Number ChanD4n132Accounts572 Wendy123Training467 JonesSarah121Training468 ChanDan132Accounts572 PatelPaul132Accounts573 (a) (a) 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)

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!

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

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

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

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

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.

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