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Fig. 12.4 Extended FBS
model: the revisited
formulation step
The Requirements Definition process (Fig. 12.3b ) , thus, starts from the complete
list of expected needs Ne i previously identified and it is made up of:
• Process V transforms the initial expected needs Ne i
into a first complete set of
Re i (transformation).
• Process VI expands the Re i set into a bigger or equal number of R e variables
(transformation).
• Process VII uses R e
and results in their interpretation R i , often through the
constructive memory.
• Process VIII transforms the subset of R i implying an active role of the product,
i.e., not related to design constraints, into F i variables (transformation).
• Process IX focuses on a subset (Re i R i ) of R i to generate an initial requirement
state space (focusing).
• Process X uses constructive memory to derive further R i .
12.4.3 Formulation
Through the integration of Needs identification and Requirements definition into
the Gero's FBS model, the Formulation step has to be updated at least for those
parts that involve Requirements. Changes, as shown in Fig. 12.4 , consist in those
processes that definitively substitute the direct processes from the external word of
R variables to the interpreted word of F i ,S i , and B i variables:
• Process XI reuses R e to obtain definitive R i (interpretation). This step is oriented
to the creation of definitively validated interpreted Requirements that can be
correctly elaborated.
 
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