12. SLC is a cycle (almost)

By now you will have read about every stage of the system life cycle.

Maintenance will continue over the life of the system.

However, eventually every system will become obsolete and so will need replacing or finally switched off.

Therefore the cycle may start all over again in order to create the new system.

The SLC may be in a nice orderly circle as depicted in the diagram. But in practice there may be many additional loops going back and forth between stages.

For example, the system may be in its testing stage but then a new or changed user requirement happens. Now part of the process needs to go back and work through the design and implementation stages once more.

Two modified versions of the method tries to take account of this looping. One is called 'the spiral method' and the other is called the 'water-fall model'