2. Identifying System Critical Issues

Read the following case study and identify issues which would be critical to the development of a supporting software system.

A bank operates an ATM (automated teller machine) cash machine.   The machine accepts and validates a user’s card and, provided it identifies a recognised account which is in credit, will issue cash up to a limit of £500 or the maximum in the account, whichever is the lower.  The card is validated by recognising the account number on the inserted card, requesting a PIN and verifying the correct PIN has been entered by contacting the bank who has issued the card, passing the account number and PIN (in encrypted form) and asking for validation- only a reply of ACCEPT or DECLINE is returned.

3. Qualities of Information Systems

Complete the following sentences.

1.  A system which forces a user to work in an unnatural manner or perform tasks in a strict sequence which cannot be altered is referred to as a (an) _____________________ system. 

2.  A system which persistently ‘crashes’ and requires restarting is a (an) _____________ system.

3.  A system which requires a small change but which takes a disproportionate time to amend is a (an) ___________________________________ system.

4. Changing Requirements

Explain why over 80% of software errors might arise from ‘requirements’.

5. Levels of Modelling

What level of modelling is being described:

An analyst describes the things, processes and circumstances under which things happen in literal terms, using the names and references used by every day users.