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Function-Structure-Behaviour frameworks

Notes about Gero's FBS framework and how it connects (or not) with my way of doing it.

This page is for notes. I'm developing a description of my own version at PFBS.


From [GK13]: “In searching for a way to think about designing, and axiom was proposed: The foundations of designing are independent of the designer, their situation, and what is being designed.”

  • This is reasonable and consistent with what I do. I might rephrase it, however, as The foundations of designing are independent of context, process, and agents.
  • This makes it much like the ideal scientific method.

From [GK13]: “Based on this axiom two hypotheses about representing designs and designing were proposed: (1) all designs could be represented in a uniform way, and (2) all designing could be represented in a uniform way.”

  • While Gero suggests there is no way (save his FBS) to attain the two hypotheses, I say they're both eminently doable in (various kinds of) logic.

From [GK13]: “The observable input and output of any design activity is a set of requirements (R) that come from outside the designer….”

  • Problem: not all requirements come from outside the designer; only the level 0 requirements - those defined at the outset and that (ought to) deal only with the behaviour of the system as a black box in a context.

From [GK06]: “Many agent-based systems are based on traditional models and theories of designing that assume the world as being fixed, well-defined and unchanged by what you do. This static view of the world is not in accord with the results of empirical design research. In order to develop computational design agents as aids to human designers, we need a model of designing in which all the knowledge is not encoded a priori and which allows for a changing world within which the agent operates. and ”…the notion of situatedness… emphasizes that the agent's view of a world changes depending on what the agent does.“

  • This is consistent with my notion of balance and of interacting systems.


From [GK13][GK06]: “Function is the teleology of the artefact (“what the artefact is for”). It is ascribed to the artefact by establishing a connection between one’s goals and the artefact’s measurable effects.”

  • I like my way better. Function, per Gero, is a human/teleological - and therefore subjective - entity. I generalize it to be the role of structure's behaviours in a context (a larger system).
  • TODO I need to be able to better describe what I mean by “role.”
    • “Role” could be something like being a transformer that consumes available inputs to produce outputs needed by other elements of the context. This connects to my notion of system-as-transformer.


From [GK13][GK06]: “Behaviour is defined as the artefact’s attributes that can be derived from its structure (“what the artefact does”). Behaviour provides measurable performance criteria for comparing different artefacts.”

  • This is entirely consistent with my notion of behaviour, even though I think I phrase it better. What an artifact does is clearly a response to stimulus; artifacts without any inputs won't do anything.
  • I say: behaviour is the response of a system to inputs from the context, and which are derived from its structure.

From [GK13]: FBS also distinguished between actual and expected behaviour (and only behaviour) as a means of capturing the design tasks associated with testing. This is important.


From [GK13]: “Structure is defined as its components and their relationships (“what the artefact consists of”).”

  • Again, I like my version more. Structure is the collection of invariant properties of a system; those things that don't change by context (within reason, because after all it's engineering).
  • Alternative: the inherent properties of a system, which are not derived from other factors.
    • This would allow the values to be variant (e.g., the behaviour of combustion causes a change in inherent properties).

Summary & Examples

It's very difficult to tell whether the definitions of function, behaviour, and structure constitute models of reality, or are assumed to be labels that denote actual real-world things.

Table 1 in [GK13] has some interesting examples.

  • TODO I really need to work out some interesting examples too. They can be added to my courseware directly.
  • TODO There's an example of window design in [GK06] that is fairly detailed. I should recycle it for my version. However, I have some concerns about the example - I've noted them in the hardcopy of the paper.

From [GK06]: ”…the designer ascribes function to behaviour and derives behaviour from structure. A direct connection between function and structure, however, is not established.“

  • This is consistent with systems thinking. Behaviour happens at interfaces; structure is internal, and function is external.

Transitions between F, B, and S

Fig. 1: A summary of mappings between concepts in Gero's FBS. Each mapping corresponds to a type of design activity.

From [GK13]: Since sometimes various disruptive cognitive processes (e.g., lateral thinking) can lead from a structure to a new insight, FBS allows for mappings from structure back to behaviour and to function.

  • I'm not sure about this one, as it's starting to get away from describing a model of reality and getting into a model of cognition.

From [GK06], below are summaries of the basic processes.

  • TODO Need to rephrase these in my vernacular.
  • I note that some of these processes aren't so much design as they are product development or engineering tasks.
    • Should we be more picky about where the boundaries are drawn around design? I think so.
  • Some of these seem problematic. For instance, synthesis transforms “expected behaviour into external structure” where “external” here means drawings and not actual product. But is this externalization really part of reality, or is it just a record of a thought because we suffer bounded rationality?

Formulation (process 1) transforms the design problem, expressed in function (F), into behaviour (Be) that is expected to enable this function. Synthesis (process 2) transforms the expected behaviour (Be) into a solution structure (S) that is intended to exhibit this desired behaviour. Analysis (process 3) derives the “actual” behaviour (Bs) from the synthesized structure (S). Evaluation (process 4) compares the behaviour derived from structure (Bs) with the expected behaviour to prepare the decision if the design solution is to be accepted. Documentation (process 5) produces the design description (D) for constructing or manufacturing the product. Reformulation type 1 (process 6) addresses changes in the design state space in terms of structure variables or ranges of values for them. Reformulation type 2 (process 7) addresses changes in the design state space in terms of behaviour variables or ranges of values for them. Reformulation type 3 (process 8) addresses changes in the design state space in terms of function variables or ranges of values for them.

The approach described in [FCS14] - the “casual relation template” - seems to imply a causative connection between behaviour and function. The structure of the template implies one verb causes another; this could well also connect behaviour to function1).

I think one of the important pieces missing from [FCS14] is any sense of context in which the analogizing is done; context of the participant's experiences and training, of the problem they have to solve, etc. FBS and PFBS seem to do better by having either situatedness or system environments baked in.

Including situated cognition

fbsfinal.jpg Fig. 2: Mappings in sFBS between 3 "worlds."

TODO I disagree with this figure, because I do not believe the 3 worlds overlap as shown except, possibly, at the end of a design. The external world contains unknown true things, and the agent may be mistaken about some things, so the interpreted and external worlds only overlap partly. The expected world is reasonably a subset of the of interpreted world, but similarly overlaps the external world only partly.

  • Indeed, one can argue that the goal of design is to reach a state where they all nest as the figure suggests.

From [GK13][GK06]: The application of situated cognition to FBS involves admitting 3 “worlds:” the external world, the interpreted world, and the expected world. These three are collections of claims that exist in the designer's mind. However, sFBS embeds the interpreted world in the external world, and the expected world in the interpreted world. I'm not sure this makes sense. Also, the whole situatedness thing isn't described in a way that is consistent with systems thinking.

  • It's not clear whether the external world is a model of reality, or actual reality.
  • The whole situated part (most of the paper, really) deals more with what goes on in the designer's head than what can be called either a normative or descriptive model of design reality.
  • It also seems not particularly consistent with a lot of the cognitive science and theory of mind stuff that I've read.
  • Really not sure about those bits.

The experiments reported ever so briefly at the end of [GK13] are not reproducible, although at least citations are provided.

From [GK06]: “The interpreted world is the world that is built up inside the designer or design agent in terms of sensory experiences, percepts and concepts. It is the internal representation of that part of the external world that the designer interacts with.”

  • So, it seems that the interpreted world is a representation of the external world. But the external world is a representation (so he says), so is the interpreted world a model of a model? Is that what he means?

TODO The notion of including beliefs by way of situated cognition just screams using an action logic to represent it all.


GK13. a, b, c, d, e, f, g, h, i, j, k J.S. Gero and U. Kannengiesser. 2013. The function-behaviour-structure ontology of design. An anthology of theories and models of design. Springer-Verlag London. Chakrabarti and Blessing, eds. pages 263-283.
GK06. a, b, c, d, e, f, g, h J.S. Gero and U. Kannengiesser. 2006. The situated function-behaviour-structure framework. Design Studies, 25:373-391.
FCS14. a, b T. Feng, H. Cheong, and L.H. Shu. 2014. Effects of abstraction on selecting relevant biological phenomena for biomimetic design. ASME J Mech Des 136(11).
This has been confirmed via email with L. Shu on 22 May 2015.
research/fbs.txt · Last modified: 2020.03.12 13:30 (external edit)