System Modeling - The Hatley Pirbhai Modeling

System models are hierarchical or layered as a system is represented at different levels of abstraction. The top level of hierarchy presents the complete system. The data objects, functions, behaviors are represented. As the hierarchy is refined or layered, component level detail is modeled and finally system models evolve into engineering models.
Hatley-Pirbhay modeling is an extension of the concept that every computer system can be modeled through the usage of an input-processing-output model by including the two additional features of user interface process and maintenance/self testing. These five components are added to a system model template to allow for modeling of the system which allows for proper assignment to the processing regions.

THE HATLEY-PIRBHAI MODELING
- The Hatley-Pirbhai model depicts input processing, and output along with the user interface and maintenance or self-test.
- It includes two more system features: user interface processing and maintenance and self-test processing.
- A system engineer can create a model of system components that sets a foundation for later steps.
- The system engineer allocates system elements to each of five processing regions within the template: user interface, input, system function and control, output, maintenance and self-test.
- A system context diagram(SCD) resides at the top level of hierarchy which defines all external producers of information used by the system,all external consumers of information created by the system and all entities that communicate through interface or perform maintenance and self-test.
- All the major subsystems are defined in a system flow diagram (SFD) which is derived from SCD.
- Information flows across the regions of system context diagram is used to guide the system engineer in developing system flow diagram.
- System flow diagram shows major subsystems and important lines of information.