This paper describes a methodology to assist in the identification of
possible conceptual design variants during redesign. The approach is b
ased on functional reasoning and involves: (1) the structural and func
tional analysis of an existing design; (2) the production of abstract
representations of functions and design entities using conceptual grap
hs; and (3) design interrogation based on a functional tree approach.
The research reported in this paper also focuses on the definition and
the representation of elementary mechanical functions. Extended Backu
s-Naur Form (EBNF) notations are used to structure in a computable for
m, the relevant information (or design knowledge) conceptualised in ei
ther the conceptual graphs or the functional trees. EBNF syntax is als
o used to formulate rules which aid the partial automation of the reas
oning process. The EBNF notations can be mapped to any programming lan
guage. A diaphragm valve is used as a case study to demonstrate the ap
proach.