Partitioning. The technique for reducing External (Intrinsic) Complexity

Partitioning as the name suggests is the technique of dividing the system into smaller parts. It is a fair assumption that each partition of the system is required to exhibit a smaller number of behaviors then the overall composite system. It is also a fair assumption that the smaller number of behaviors required of each sub-system will result in a less complex design for each system.

It is in this indirect way that Partitioning leads to a lower complexity.

It must be noted that partitioning imposes an integration cost on the system.  The partitioned systems need to be integrated with each other for the system to work.  This means that in effect, a two step hierarchy of systems is created. At the lower step are the individual partitioned systems each of which is made up of its own set of interacting elements. At the higher level is the system of these interacting partitioned systems.  

It needs to be noted though that Partitioning if improperly done can increase complexity. This can happen, if each sub-system provides similar services as a result of which there is need to create similar objects (programs) in each partition.

This technique works because each partitioned system being simpler lends itself to better comprehension and therefore better design.