Elementary Process:

A software application is in essence a defined set of elementary processes. When these elementary processes are combined they interact to form what we call a software system or software application. An elementary process is not totally independent existing alone, but the elementary processes are woven together becoming interdependent. There are two basic types of elementary processes (data in motion and data at rest) in a software application. Data in motion has the characteristic of moving data inside to outside the application boundary or outside to inside the application boundary. An elementary process is similar to an acceptance test case.