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250 PART THREE CONVENTIONAL METHODS FOR SOFTWARE ENGINEERING

1. Assumptions that reduce the number of possible permutations and variations,
thus enabling a model to reflect the problem in a reasonable manner. As an
example, consider a three-dimensional rendering product used by the enter-
tainment industry to create realistic animation. One domain of the product
enables the representation of 3D human forms. Input to this domain encom-
passes the ability to specify movement from a live human actor, from video,
or by the creation of graphical models. The system engineer makes certain
assumptions about the range of allowable human movement (e.g., legs can-
not be wrapped around the torso) so that the range of inputs and processing
can be limited.
2. Simplifications that enable the model to be created in a timely manner. To
illustrate, consider an office products company that sells and services a broad
range of copiers, faxes, and related equipment. The system engineer is mod-
A system engineer eling the needs of the service organization and is working to understand the
considers the following
factors when flow of information that spawns a service order. Although a service order can
developing alternative be derived from many origins, the engineer categorizes only two sources:
solutions: assumptions, internal demand and external request. This enables a simplified partitioning
simplifications, of input that is required to generate the service order.
limitations, constraints,
and customer 3. Limitations that help to bound the system. For example, an aircraft avionics
preferences. system is being modeled for a next generation aircraft. Since the aircraft will
be a two-engine design, the monitoring domain for propulsion will be mod-
eled to accommodate a maximum of two engines and associated redundant
systems.
4. Constraints that will guide the manner in which the model is created and the
approach taken when the model is implemented. For example, the technol-
ogy infrastructure for the three-dimensional rendering system described pre-
viously is a single G4-based processor. The computational complexity of
problems must be constrained to fit within the processing bounds imposed by
the processor.
5. Preferences that indicate the preferred architecture for all data, functions, and
technology. The preferred solution sometimes comes into conflict with other
restraining factors. Yet, customer satisfaction is often predicated on the
degree to which the preferred approach is realized.

The resultant system model (at any view) may call for a completely automated
solution, a semi-automated solution, or a nonautomated approach. In fact, it is often
possible to characterize models of each type that serve as alternative solutions to the
problem at hand. In essence, the system engineer simply modifies the relative influ-
ence of different system elements (people, hardware, software) to derive models of
each type.