Beyond Engineering Bias: designing a
tool to liberate conceptual design
Martin Stacey1
Marian Petre1
George Rzevski2,
Helen Sharp1
Rodney Buckland2
Computing Department & 2Design Discipline
The Open University
Milton Keynes MK7 6AA, United Kingdom
Telephone: +44 1908 653037
Fax: +44 1908 652140
Email: {m.k.stacey, m.petre, g.rzevski, h.c.sharp, r.buckland}
@open.ac.uk
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Published in
A. Blandford & H. Thimbleby (eds)
HCI'96 Industry Day and Adjunct Proceedings
School of Computing Science, Middlesex University, pp 173-180,
1996.
Open University Computing Department Research Report 96/04
Abstract. The FACADE project is developing a prototype support system for the
conceptual design of mechatronic systems, which is designed both to mitigate and
exploit the inevitable biasing effects of design tools on design processes. It
includes a suite of design environments supporting different visual representations,
to help designers escape the restrictions of any one formalism. As far as possible
the system avoids restricting the order in which designers perform tasks, and it
allows them to mix concepts at different abstraction levels, in order to allow them
to adopt structured methodologies without being tied to them, and to design by
modifying previous versions. The system includes a design environment designed
to help and encourage engineers to think about mechatronic systems as networks of
flows of matter, energy and information.
Keywords: HCI, design, CAD, mechatronics.
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M.K. Stacey, M. Petre, G. Rzevski, H.C. Sharp, R.A. Buckland
1. Introduction: recognising bias
The tools designers use can influence the processes by which designs are created, and
influence the designs themselves. Some set out to do so, dictating a methodology or
embodying a theory of design. Others do so inadvertently. Recognising the inevitability of
bias in tools, the FACADE project argues that the interfaces to design tools should be
designed to take account of how they bias design. Indeed bias should be exploited. Biases
seen as useful for a given design task should be enhanced, while harmful biases should be
avoided as far as possible.
The FACADE project (Rzevski, 1995; Stacey et al., 1996) is developing a prototype
tool to support ideas capture in conceptual design in engineering, in a way that both uses
and mitigates bias. This prototype provides different visual representations supporting
different views of designs (as in figure 1), with AI support for propagating constraints and
checking consistency between them. This is both to help individual designers escape the
biases produced by any one representation, and to address the problems of communication
among engineers from different disciplines who have different perspectives and cultures,
and use different representations.
s
c
r
e
e
n
Figure 1. A Suite of Design Environments
2. Engineering bias in tools
Any formalism is a simplification, providing a simple way of dealing with a complex thing,
and particular formalisms both ease and impede users’ ability to express particular ideas,
making some information easier to express at the expense of other information. This is
particularly true of formalisms designed to accommodate engineering products that are so
Beyond Engineering Bias
3
complex that any mental representation includes only some aspects of the machine. Hence,
no one formalism or attendant representation will suit every problem; no one formalism
will make easier the whole set of problems that people solve with computers. Petre and
Green (1992) stress “escape from formalism” as an essential part of real-life, professionallevel design, necessary to cope with things not accessible within a given formalism. Expert
designer behaviour shows deliberate shifts among representations and reasoning styles in
order to address easily different aspects of a problem (Petre, 1994). Thus, expert designers
manage to evade the bias inherent in their tools, or to work with it. But less expert
designers may not be as able to evade such biases, and so the choice of tools may well
constrain their space of possible solutions.
Considering the results of design processes, Stacey (1995) argues that designers are
inevitably pushed into producing some designs rather than others by the unevenness of their
tools: how the tools make some designs easier to create than others that are equally simple
and obvious. All design tools are uneven, from pencils to three-dimensional surface
modelling systems. Unevenness can only be defined in relation to a designer’s goals and
conception of the design domain. The unevenness of a design tool pushes designers toward
particular parts of the spaces of possible designs that are defined by the forms and
relationships in the designer’s mental representations of designs, and the designer’s mental
operations for transforming and combining them. The level of bias depends largely on the
closeness of mapping between the designer’s mental representations and the design
elements and operations for combining them provided by the tool.
3. Tools to support structured design methodologies
The main thrust of previous research on computer support for conceptual design in
mechatronics has been to develop tools that use formal representations, and support and
impose top-down structured design methodologies (for instance Hildre and Aaslund, 1995).
They have been motivated by prescriptive theories of mechatronic design (see Buur, 1990,
for a review) rather than by studies of how designers think. They have been intended to
encourage or force engineers to explore more of the space of possible designs, at a skeletal
abstract level, before selecting a single outline design for detailed development. They
require engineers to construct skeletal designs using particular abstract categories of
mechanical and electronic functions, and then to develop abstractly specified designs in
particular ways.
The Modessa system (Kersten, 1995) embodies a design methodology called
'morphological overview', in which the different ways to perform an industrial task are
listed, and each is recursively decomposed into subtasks with alternative ways to do them.
Modessa is designed to record company knowledge about task solutions, and support the
rating and selection of appropriate solutions, to encourage the reuse of pre-existing solution
chunks. Schemebuilder (for instance, Bracewell et al., 1993, 1995) represents components
of mechatronic systems in abstract terms as bond graph elements that perform particular
transformations; these functional components are made more concrete by decomposing
them into subcomponents and selecting particular types of mechanism to perform them
(Sharpe and Bracewell, 1993). MAX (de Vries, 1994) pays more attention to the
psychology of design; it embodies a more flexible formalist approach, combining bond
graphs with iconic diagrams, that also imposes top down abstract design. Both
Schemebuilder and MAX require designers to use abstract formal languages to describe
machine behaviour.
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M.K. Stacey, M. Petre, G. Rzevski, H.C. Sharp, R.A. Buckland
4. An alternative view
Our view is that design tools should enable the use of more ‘natural’ conceptual categories.
The concepts real engineers use cut across the formal categories of mechatronic theory
(Rzevski et al., 1995). While machine-understandable languages for describing designs
have an important role to play in computer support for design (de Vries, 1994), they need to
express relationships that designers find it ‘natural’ to think in (Stacey, 1995b). Moreover,
designers should not be restricted to any one set of conceptual categories; they need to be
free to switch between design environments with alternative visual representations
supporting different conceptualisations of the design. A tool should support fluent idea
capture and the expression of provisionality in designs.
A tool for experts should also allow them the maximum latitude in process as well
as conceptualisation. Design is non-linear or ‘opportunistic’ (for instance, Visser, 1990),
and experts reason at many levels of abstraction, moving readily between them (for
instance, Petre, 1993), so a design tool should allow designers to use concepts at any level
of abstraction at any time, and to use concepts at different levels of abstraction at the same
time.
5. The FACADE System
The FACADE system is designed to take advantage of some useful biasing effects within
particular representations but to mitigate biasing effects overall by supporting multiple
representations and facilitating mapping between them, and by avoiding imposing a design
methodology or order of working. Our approach permits designers to employ or abandon a
structured methodology at need; or to design middle-out beginning with relatively concrete
initial ideas or with a previous design. It also enables designers to combine concepts at
different levels of abstraction. The prototype tool includes a set of alternative design
environments designed to enable engineers to think in particular ways about mechatronic
systems (as in figure 1), linked by a set of AI modules for translating between
representations, propagating constraints and checking consistency, and by a single internal
design representation including a product model encoded in the DROOL representation
scheme (Stacey et al., 1996).
Any computer tool for conceptual design can only support a limited subset of the
potentially useful representations of engineering systems and design transformation
operations. It embodies a hypothesis that the representations and the operations on them
that it provides are useful; and it biases designers into thinking about designs using mental
representations that are compatible with them. The FACADE System embodies the
hypotheses that, for a wide range of mechatronic systems, the essential decisions in
conceptual design are what the major components of the systems are and what they do, and
how they are connected, and that these decisions precede spatial layout design.
6. Alternative design environments
We are currently concentrating on developing two design environments for the FACADE
System, for Concept Arrays and Blob Diagrams, which make different aspects of
conceptual designs explicit. These were chosen as two useful visual representations, one
largely textual and one largely graphical, different enough to demonstrate the feasibility of
the underlying representation and mapping mechanisms. But the underlying representation
is generic, intended to allow a greater variety of representations, and plans include other
environments embodying other representations.
Beyond Engineering Bias
5
6.1. Concept Arrays
One design environment enables designers to construct Concept Arrays (Rzevski, 1995b),
which push designers to think about mechatronic systems as networks of components that
process and transmit matter, energy and information, that together comprise a set of
interlocking flows of matter, energy and information. (In this view, the concepts in
conceptual design are abstractions of physical components participating in these flows.)
This conception of the structure of machines is one part of Andreasen's (1980) Theory of
Domains, a central contribution to the theory of mechatronics (see Buur, 1990, for a
review). We argue that thinking in terms of flows encourages designers to explore the
spaces of possible alternative solutions and consider the completeness and integrity of their
designs without being forced either to use unnatural formalisms or awkward orderings of
tasks. So we adopt it as a primary view to be used and supported in conceptual design
(Rzevski, 1995b; Rzevski et al., 1995), and are developing both design environments and
reasoning mechanisms to encourage designers to use it (Stacey et al., 1996).
Information
Energy
Matter
Input
CCD Camera with
thin-film filters for
IR and visible
500W Solar arrays
(Propellant loaded
at launch site)
Storage
32 MByte RAM
Tape recorder
Ni-Cd battery
Momentum wheels
S/c orbit
Spherical propellant tanks
Processing/
Conversion
JPEG Image
Electrical heaters
20N thrusters
compression
Transmitter SSAs
Articulation drives
for attitude control
200N thrusters
20N thrusters
for orbit control
200N thrusters
Transfer/
Transmission
S/c transmitter in
Regulated 28V
Pressurised propellant
Ka band
power bus
transfer system
Use
S/c power bus
Payload
Disposal
S/c heat pipes
(S/c to parking orbit at EOL)
Figure 2. A Concept Array for FireSat
In Concept Arrays, concepts are named and located in cells that indicate their
roles within the network of flows of matter, energy and information. The components of a
mechatronic system can input, store, process or convert, transfer, use or dispose of matter,
energy or information. The array shown in figure 2 shows the major flows of matter (fuel),
energy (electric current, heat and kinetic energy) and information (camera images) for a
satellite (Rzevski and Buckland, 1995). In a Concept Array the links between the different
components participating in a flow are only implicit, though membership of one particular
flow may be indicated by highlighting. One component may participate in several flows, so
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M.K. Stacey, M. Petre, G. Rzevski, H.C. Sharp, R.A. Buckland
it can appear in more than one place in a Concept Array. Concepts are named or referred to
by writing in a cell; additional information is supplied by selecting switches and listing
characteristics in a dialogue window.
Example of the sort of sketches engineers have been observed to make in discussions about
multidisciplinary system design. Within this system architecture scenario for a signal
processing design for audio, different representations, physical and logical entities, and
different levels of abstraction are intermixed as needed.
A
B
C
D
E
F
Gain control Circuit inside I/O board
Split to three outputs
To signal processor (transfer function)
G
H
I
J
K
Type of message
Type of message
Control by human
To input/output (transfer function)
Type of message
To display
Display
Individual instruction inside signal processor shown as object
Figure 3. A Blob Diagram
Beyond Engineering Bias
7
We envisage the use of a sequence of concept arrays, recording initial requirements
in the first array and more concrete requirements and concepts in subsequent arrays. When
concepts have been selected for the particular flows, the construction of Concept Arrays
can be repeated recursively for the subsidiary flows needed to make the primary flow work.
6.2. Blob Diagrams
Many designers record ideas by drawing schematic diagrams including rough sketches,
symbols or icons, and the relationships between them; figure 3 shows an example. We call
these ‘blob’ diagrams to avoid making any commitment about what the elements of the
drawing are; their shapes are frequently unimportant or are symbols rather than pictures.
Lines between the blobs represent connections of some sort; they may denote physical
conduits for, say, electricity or fuel, or functional relationships like 'powers' or 'stabilises'.
We are developing a blob diagram environment based on a conventional drawing package,
to enable designers to draw design elements and connections with some of the freedom
provided by the backs of envelopes. Designers can draw blobs that mean anything they
want, so they are not restricted to any particular conceptualisation. The blob diagram
environment enables the designers to identify elements of their drawings as concepts or
connections and name them, and then list their characteristics or parameters, for example to
state the roles they play in the flows of energy, matter and information in the system (and
hence relate them to an associated Concept Array).
7. Summary
The FACADE System is a prototype computer support tool for the conceptual design of
mechatronic systems designed to minimise the biasing effects of design tools. It restricts
designers' order of actions as little as possible, to allow them to use or escape from any
methodology they find useful, by supporting provisionality and the mixture of abstraction
levels. It allows designers to swap freely between different visual representations
supporting different views of designs, so that designers are never locked into one
conceptualisation. It is also designed to exploit bias in ways we consider useful, by
providing design environments and reasoning mechanisms that encourage designers to
think of mechatronic systems as networks of flows.
Acknowledgements
This research was supported by EPSRC grant GR/J48689 to George Rzevski, Helen Sharp
and Marian Petre, for the FACADE Project (FAcilitating Communication among Domains
of Engineering). The first author has benefited from many discussions with Claudia Eckert,
who also commented helpfully on earlier drafts of the paper.
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