Functional modelling vs Dependency structure models for ME systems

September 24, 2011

Has it ever happened to you that your waiting for coffee and the person next to you turns out to be a really interesting authority on something so complex you can hardly understand what they are talking about?  I had an experience like that a few weeks ago in Washington DC, with a man who teaches product design method and theory in Luxemborg.  I have some reading to do before I understand how these different appproaches to system models can help me, but I share the email I received so you might comment or develop some ideas as well.

From: Kilian GERICKE

Sent: Monday, September 12, 2011 1:18 AM


Subject: Design methods


Dear Mr


Picking up
our conversation during breakfast in Washington I would like to recommend two
approaches which might be interesting for your work.

As I
understood, you are working currently as a consultant for projects on energy
efficiency improvement of buildings. I am not an expert in building design and
energy efficiency but I would compare such projects with redesign projects in
mechanical engineering.


Given that
we deal with a building as a system that consists of different subsystems
(climate control unit, water treatment unit,  structure, facade, etc.) I
would expect that a major challenge in such a project is to understand the
dependencies between these sub-systems. I know there are many other challenges
but let me focus on this one.


mechanical engineering two ways of modelling systems are widely applied:
functional modelling and dependency modelling. Both approaches are intended to
represent a complex system in an abstract way, thus reducing complexity.


modelling represents a system only by the functions that are fulfilled not by
the means which are chosen in order to realise the functions. The functions are
represented as boxes which are connected by arrows. The arrows represent
different flows (material, energy, information). Such a model is called
function structure.

Because no
means are modelled a function structure is solution neutral. The solution
neutral representation is interesting for a redesign project, because it
reduces the tendency to stick to known solutions.

I expect
that you know this type of modelling – perhaps with a different name. Pahl and
Beitz’ extension is the differentiation between different flows (material,
energy, information).

A good
introduction into functional modelling is given in:

  • Pahl, G.; Beitz, W.; Feldhusen, J.; Grote, K. H. (2007): Engineering
    Design – A Systematic Approach. Berlin: Springer-Ve


(design) structure modelling (DSM):

(also design) structure modelling represents the dependencies between subsystems
in a matrix-format. A Dependency (Design) Structure Matrix can be used to model
every type of dependency – usually focussing on only one dependency at the same
time – but different extensions to the basic DSM have been proposed in the last

A DSM allows
you to assess changes of sub-systems and the propagation of effects of changes
on other sub-systems.

You can
find information about DSM in:

  • Ulrich, K. T.; Eppinger, S. D. (2007): Product Design and Development:

And on


I think a
combination of functional modelling and DSMs is an interesting option for your


I hope
these approaches are interesting for you. I would like to know whether you
already knew them before and whether they are helpful for your work or not.






Dr.-Ing. Kilian Gericke

Research associate


Research Unit in Engineering

University of Luxembourg

Campus Kirchberg

6, rue Richard Coudenhove Kalergi, L-1359

Tel: (+352) 46 66 44 5791,
Fax: (+352) 46 66 44 5200



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