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What - Functional Dependency Modeling refers
to the approach whereby the functionality of a system is captured in a model,
rather than trying to describe its failures. This concept follows the logic
that it is easier to describe how a system works than to describe how a system
fails.
Why - Functional Dependency Models are the
first step towards allowing conceptual designs to be entered, without having to
rebuild the whole model for later analyses. The drawback to a functional-only
model is that it does not allow failure modes to be added, which can affect how
the model is built and the degree to which diagnostics can match real-world
testing.
When - Functional Dependency Models are
easily built during concept phase for up-front optimization. The ability for
the functional dependency model to support analysis throughout the design
process depends on the degree to which failure mode testing is performed.
Failure mode testing mandates that the functional model be changed in some way
that could obfuscate the model. Also, because failure modes can not be directly
handled, FMECAs are not easily integrated, making this model less amenable to
support reliability engineering efforts.
History - The Functional Dependency Model
was first formalized in the 1990's by a product called eXpress. This product
was another product of the Dependency Modeling approach, its predecessor being
called "STAT"--a pure dependency modeling tool. It is noteworthy that due to
the limitation of not being able to enter failure modes, the eXpress tool has
already moved into a Hybrid Model approach.
Related Links -
Failure Mode Dependency Models, Hybrid
Models
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