The diagram shows specializations of General Function and General Functional Usage

Concept	Documentation
System Function	Specifies the fundamental action or task that have to take place in the System in accepting and processing the inputs and in processing and generating the outputs. A System Function * accepts input from the System boundary * exposes its output at the System boundary * changes the System's State * is dependent on System's State Note: A System Function does not need to expose observable output, when it changes the System's state in a way that is observable by other system functions. Furthermore, a System Function does not need to accept any input from the system boundary, when it is dependent on the System State, which in turn is changeable by other System Functions.
General Functional Usage	Specifies a General Usage of a General Function within one or more other General Functions.
System Process	Specifies the fact that a System Process captures system behavior as a specific sequence of actions or tasks, and system exchanges including information, materials, energy, etc.
System Partial Function	Specifies the fact that a System Partial Function is a decomposed part of a System Function and defines details of the System Function it belongs to.
Context Function	Specifies the fact that a fundamental action or task is expected to be carried out by an External Entity. Note: The intention is to capture the expectations and to explicitly dissect the functionality. This must not be interpreted as an attempt for a behavior specification of an External Entity. Capturing this valuable information is the basis to reach agreement on the functionality at the System boundary by clarifying the expectations about what is performed by Context Elements.
General Function	Specifies a General Function. It is used as base Class for specific System or Context Functions, or Partial Functions.
System Function in System Process	Specifies the fact that a System Function is used in a System Process.
Context Function in System Process	Specifies the fact that a Context Function is used in a System Process.
System Partial Function in System Function	Specifies that a System Partial Function is used in a system function