Design and development of systems.

Upward design. This design refers to identifying the processes that need to be computerized as they arise, analyzing them as systems and coding processes or buying packaged software to solve the immediate problem. The ascending name refers to the lower level in which computerization is first introduced. When internal programming is done with an ascending approach, it is difficult to interconnect the subsystems so that they perform easily as a system. It is very expensive to correct the interconnection faults and many of them are not discovered until the programming is completed, when the analysts try to gather the system on the deadline indicated for the delivery. In this situation, there is little time, budget or patience of the user for the debugging of delicate interconnections that have been ignored.

Descending design. The top-down design allows system analysts to first determine global organizational objectives, as well as determine how they best meet in a global system. Then the analyst divides said system into subsystems and their requirements.

Modular Development. This approach involves dividing the programming into logical and manageable parts called modules. This type of programming works well with the descending design because it emphasizes the interfaces between the modules and does not neglect them until the end of the systems development. Ideally, each individual module must be functionally cohesive so as to perform a single function.

Use of structure diagrams to design systems.

The numbers (000, 100, 200) represent the modules.

The lines represent right angles.

The insertion of adjacent modules decreases from the parent module.

On the sides of the connection lines, two types of arrows are drawn. Arrows with empty circles are called data pairs and arrows with filled circles are called control flags or switches. A switch is the same as a control flag except that it is limited by two values: yes or no. These arrows indicate that something is passed down to the lower module or up to the upper module.