Modelling (pre-)Design Activities With a Multi-Stakeholder Perspective - Principia Designae: Pre-Design, Design, and Post-Design - page 172

than a translations of some requirements into a functional specification. In other terms,
the first task accomplished a design agent, i.e., identification of user's intentional aims
and desires is not adequately represented into the FBS design framework.
These considerations support the authors' intention to integrate, within the FBS
framework, an explicit representation of Needs and Requirements to have proper
means to model the entire product development process from the earliest stages
using the same formalism already proposed by Gero and Kannengiesser. Starting
from these observations, the authors have formulated a proposal for an extended
FBS model, characterized by two further types of variables and their related
processes, as detailed in the following section.
12.4 The Extended FBS Model
According to the objectives of the present work and to the limitations of the FBS
framework discussed in the previous section, the authors have proposed the inte-
gration of two further explicit classes of variables (Cascini et al. 2013 ).
• Needs (N): an expression of a perceived undesirable situation to be avoided or a
desirable situation to be attained. This situation can be perceived by any of the
actors involved in the product life from the purchasing phase to each stage of use
and disposal. Needs can be explicitly stated to the designer or perceived by the
designer because of being extracted (or even postulated) by the observation of
users' behaviour.
• Requirements (R): a measurable property related to one or more Needs. They
“are structured and formalised information about a product” and “consist of a
metric and a value”.
These two new sets of variables intend to investigate, as in the proposal of
Vermaas and Dorst ( 2007 ) , the concept “what it is for”. This expression in Gero and
Kannengiesser ( 2004 ) is considered sufficient to define Function, but as Vermaas
and Dorst claim, everyday descriptions of the use of artefacts distinguish between
purposes and functions. “Lasers are nowadays used as pointers during slide pre-
sentations. If such use is described, one can say that the laser's purpose is to
highlight locations on projection screens, whereas its function is still to produce
light. Then, purpose and function indeed refer to two different things, which
becomes manifest when the use of the pointer fails, say because there is too much
light falling on the projection screen: assuming that the laser still emits its regular
amount of light, one can then say that the laser fails to achieve its purpose but not its
function” (Vermaas and Dorst 2007 ).
The Formulation phase (the interpretation of the requirements and the related
transformation into functions, behaviours and structures), in the design process,
requires formalisation in addition to interpretation. The original FBS model con-
siders the activity of interpretation, but does not take into account the formalisation
effort. Only formalisation can convert interpretations into formalised requirements
descriptions from needs.