Files used in applications are vital to the running of a system. Any loss or corruption of data will have serious or fatal implications for the performance of the application. Delays, loss of business and possible legal action may result. For these reasons many safeguards are used to protect files from:

• Hardware failures
• Software failures
• Human Errors
• Deliberate damage.

There are numerous methods of file security :

• Physical security
• File backup
• Transaction Log
• Archiving
• Passwords
• Encryption

Physical Security

• Security guards
• Alarm systems
• Locks on rooms and on computers
• Access to rooms by swipe cards / fingerprint scan / retina scan
• Write-protect mechanisms

File Backup.

One straightforward method is to make a backup copy of all your important files.

Generations of Files.

If an application, such as a payroll, uses sequential files then a suitable method of file security is the Grandfather, Father, Son method. Every time a master file is updated, the original file is copied together with any changes ( held on the transaction file) to a new master file. This new master file is cal!ed the 'Son' and the previous master file the 'Father'. The next time the files are updated a new son is produced, the old 'Son' becomes the 'Father', and the old 'Father' becomes the 'Grandfather'. There now exists three generations of the master file.

If the new master file becomes corrupted, lost or damaged it can be regenerated from its father together with the relevant transaction file, which has to be kept. This process usua!ly only proceeds for 3 or 4 generations at which point the tapes are reused. However, large DP organisations such as the DVLC keep up to 19 generations of files.

Transaction Logs

An on-line system, such as a theatre seat booking system, or a cash-card system can use a transaction log to keep a record of all the transactions that have taken place in a day.

Then if the database becomes corrupted, the latest backup of the database can be updated using this transaction log.

Archive Files

In some applications, such as a Banking system for current accounts, data such as the details of the customers account from the previous year will not be held on-line but copied from disc storage, or a mass storage device, onto magnetic tape and held in a fire-proof, water-proof safe away from the Bank's computer centre. Data may be needed for historical purposes, perhaps for auditors.

The process of copying and storing files of data that are no longer in use, on a secure medium in a safe place is called archiving.

Passwords - Levels of permitted access

It is important that data is only accesses by authorised people so safeguards need to be created to ensure this.

In order to gain access to the system a user is supplied with a user name or ID together with a personal password. Some files may be open for reading by anyone, others only by those users in the same department, and others only for reading by individuals, such as 'mail'. The main computer's operating system makes sure that file access is appropriate for the user's password.

Encryption

To maintain file security when data is transferred from one computer to another using a communications link the data can be encrypted, or scrambled. This means that the data is encoded in some way before it is sent, and therefore meaningless to anyone intercepting the message. The data is then decoded at the receiving end.

Data encryption can also be used when data is stored on a file.