Modes of Processing

Transactions  Transactions are events which need to be recorded with the production, sale and distribution of goods and services. Examples include: – Buying an item in a store – Paying a gas bill – Taking out a library book – Applying for a driving licence – Enrolling on a college course – Applying for a University place – Notifying a new employer of your full name, address and bank account details – Clocking in and out from work

Master files and transaction files  Master file –Collection of records holding information about an entity such as a person or good.  T ransaction file –Holds information about events occurring in the organisation. –For employee payroll file, basically two kinds of transactions: Weekly / fortnightly transaction file with information of hours worked – used to calculate employees wages or salary. Occasional other transactions to process – additions, changes and deletions to the file. – When new employee is hired, new record must be added – When employee leaves, their record is deleted – Employee may change address, bank account, etc.

Batch Processing  Typical, large-scale batch system where data is collected on paper documents (such as applications for renewal of a TV or driver’s licence) has following stages: – The paper documents are collected into batches of say 50, checked, control totals and hash totals calculated and written on a batch header document. – The data is keyed in off-line and validated by a computer program. It is stored on a transaction file. – The data is verified by being entered a second time by a different operator. Any discrepancies are corrected. – Transaction file is transferred to the main computer. This may be physically or electronically between computers.

Batch Processing (cont.) – Processing begins at a scheduled time – maybe overnight when the computer is not busy dealing with on-line users. All the processing steps (beginning with the next) can take place without operator intervention. – Transaction file may be sorted into same sequence as master file to speed up the processing of the data. – The master file is updated. – Any required reports are produced.

Interactive Processing  Data is entered and processed straight away. –Organisations such as insurance companies are often able to make changes to a customer’s household insurance, for example, while the customer is on the phone. A report of the change would be automatically generated and a copy sent to the customer. –Some interactive systems allow queries to be made, but cannot process transactions right away. E.g. Cashpoint machines which allow you to query your balance and withdraw cash but do not update the balance until late at night; Point-of-sale terminals which can access a stock file to look up the description and price of an article when the bar-coded label is scanned, but do not alter the quantity in stock when a sale is made. (This is done later in batch mode.)

Real-time & Pseudo real-time processing  Real-time Processing – Computer responds instantly, for example to changes indicated by sensors and probes in life-support systems or aircraft control systems.  Pseudo Real-time Processing – Computer records a transaction and more or less immediately updates the master file (not instantly) A delay of a few seconds is quite acceptable for selling tomatoes in Sainsbury’s or borrowing a library book, unlike genuine real-time processing. Example - British Airways Booking System.

Choice of processing mode  Choice between batch or pseudo real-time depends on: – Does information obtained from the system need to be up-to-date at all times. – The scale of the operation - Batch systems well suited to very high volumes of data, when economical to have an off- line key-to-disk system for data entry. – Cost - Real-time system is generally more expensive because of more complex backup and recovery procedures required to cope with power failures or breakdowns. – Computer usage - Batch system can make use of spare computer capacity overnight or when computer would otherwise be idle. Common on mainframe computers. – Many applications use a combination of batch and interactive processing.