Page 156 - DCAP405_SOFTWARE_ENGINEERING

Unit 9: System Engineering

Self Assessment Notes

Fill in the blanks:
4. Classification model showing how entities have …………………… characteristics.
5. ……………………………. models show the a system and its relationship with other systems.

6. …………………… are used to model the system’s data processing.
7. No specific notation provided in the ……………….. but objects and associations can be
used.

9.3 System Modeling

9.3.1 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-Pirbhai 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 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.

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