5 Conceptual and Embodiment Design
5.1 Conceptual Design
5.1.1 Establishing Function Structures
For the purpose of defining and solving the problem, the notion of a function is essential.
Originally, the concept of functions was developed by the discipline of philosophy. Accord-ingly, a function “explains the presence of an item (organ, mechanism, process or whatever) […]” (Cummins 1975, 741) that it represents. “For something to perform its function is for it to have certain effects on a containing system, which effects contribute to the performance of some activity of, or the maintenance of some condition in that containing system” (Cummins 1975, 741). In other words, a function explains the presence of an entity, which is part of a system by pointing out that the entity is necessary, because it has some specific effect on the system. From this it can be stated that a function is a black box describing the static input-output relationship of an entity (say for example, a machine, plant, assembly, or position). The entity receives inputs (e.g. signal, energy or material) and processes the inputs into a specific output (e.g. signal, energy or material). A functional description of an entity allows the ab-stract specification, independent of implementation details. The popularity of the functional approach in design178 stems from at least three sources (Stone and Wood 2000):
177 Note that the process proposed in Figure 22 is based on the approach defined by Pahl and Beitz, although some activities are different (e.g. business analysis). These changes reflect the peculiarities of the market engineering process. Nonetheless, the changes are not fundamental such that the character of the engi-neering design process remains unchanged.
178 Not only the methodology suggested by Pahl and Beitz but also the Axiomatic Design and General De-sign theory proposed by Yosihikawa follow a functional approach (Kikuchi 2003)
• Fostering understanding
The functional approach helps the designer to understand the design problem in its en-tirety. This understanding may prevent that the designer finds excellent solutions – but to the wrong problem (Cross 1994; Summers, Vargas-Hernández et al. 2001).
• Early design decisions
By means of the functional approach the design object can be abstractly represented de-spite incomplete information. As such, it is possible to break the design problem down and make decisions early in the design process. Early decisions upon the concept are de-sirable, as the design process can abandon inadequate concepts right at the beginning.
• Creativity in concept generation
The ability to abstract the design object grants the creativity of generating innovative de-sign solutions (Ullman 1997). As the functional descriptions are independent of any par-ticular solution, the designer is free to construct completely new solutions.
Overall function
Sub-function ...
Sub-function ....
Sub-function ...
Complexity
Input Flows
Signals Information Material
Output Flows
Signals‘
Information‘
Material‘
Figure 23: Function Structure (cf. Pahl and Beitz 1984)
Design methodologies use the notion of the overall function characterizing general input-output relationship of the design object (Stone and Wood 2000). Typically, the overall func-tion is stated in verb-object form. When complex solufunc-tions are to be designed, the overall function can also be very complex. Hence, it is the idea of the functional analysis to decom-pose the overall function into sub-functions. The sub-functions thereby describe a part of the overall function representing a more elementary aspect of the design object. Aggregating over all sub-functions yields the function structure (see Figure 23). Apparently, the function struc-tures reflect the “meaningful and compatible combination of sub-functions into an overall function [...], which may be varied to satisfy the overall function” (Pahl and Beitz 1984).
Setting up the function structure is thus a central task in conceptual design. The approaches discussed in literature vary considerably (Suh 1990; Stone and Wood 2000; Kurfman, Rajan et al. 2001; Stone, McAdams et al. 2004). In the sequel, the approach developed by Pahl and Beitz and refined by Stone and Wood is followed (Pahl and Beitz 1984; Stone and Wood
2000). Despite its drawbacks179 it is easy to understand and, moreover, adequate for market engineering.
Accordingly, the establishment of the function structure follows three operations.
Operation 1 – Generate Black Box Model
The first operation is concerned with the establishment of the overall function as a black box model. Thereby, the operation of the function is described in natural language as well as the input and output flows associated with the function (c.f. Figure 23).
Flows, in general, represent the entities and quantities that are in- and output of the function.
In engineering design it is referred to the flow of energy, material and information (Pahl and Beitz 1984). While energy and material is undisputed, engineering design understands infor-mation as signals that carry inforinfor-mation for controlling purposes conveying either status or control information (Stone and Wood 2000). In market engineering, information becomes an input comparable with material that is processed along the market process. In such a case in-formation is not only a (control) signal, but also the immaterial “matter” that is processed. As such, the information flow is introduced as counterpart to material.
The input-output flows of the overall function are straightforward to obtain, as they are part of the requirement analysis. Describing the internal processes as black box appears to be ade-quate, since the requirement analysis only rarely gives advice about how to achieve the over-all function.
Operation 2 – Breaking up into sub-functions
Having stated the overall function, it must be broken up into simpler sub-functions. In princi-ple, three design problems can be distinguished according to the relative degree of novelty of the problem (Pahl and Beitz 1984).
• Original design
In the case of original design the problem is not fully understood, such that neither the sub-functions nor their ordering is generally known. Establishing the function structure of the problem denotes the most critical task in the conceptual phase.
• Adaptive design
In the case of adaptive design the function structure of the problem is much better known.
The sub-functions as well as their assembly can principally be acquired by a thorough analysis of previous, somewhat similar designs. As such, establishing the function struc-ture of the problem comprises adaptations of the original-design by introducing, replacing, or omitting sub-functions.
• Variant design
In the case of variant design the function structure of the problem is fully understood and known. This implies that the involved sub-functions used as building blocks and their as-semblies are known. Design focuses on different solutions of the particular sub-functions.
As such, it is firstly checked whether the design problem resembles previous ones. If the new problem matches with a previous design problem, the precedent function structure can be used as a basis, where adaptations and variants are possible. If the problem is new, the deriva-tion of the funcderiva-tion structures is rather difficult. The systematic approach developed by Pahl and Beitz suggests the derivation of functions along the input flows beginning “with sub-functions whose inputs and outputs cross the assumed system boundary. From these we can determine the inputs and outputs for neighbouring functions, in other words, work from the
179 Two major drawbacks are frequently noted in literature: (1) the resulting function structure is not com-pelling, in a way that different designers establish different structures (Tate 1999), and (2) the resulting function structure is not precise, as the use of terminology can vary from designer to designer.
system boundary inward” (Pahl and Beitz 1984). For reducing the ambiguities associated with the sub-functions definitions, the sub-functions of the chain are expressed in the terminology proposed in Table 8, which relies on the work of Stone and Wood (Stone and Wood 2000).180 The basic functions thereby denote the primitive tasks of sub-functions, which can be catego-rized according to the classes.
Class Basic
Func-tions Description
Separate Isolates material or information into distinct component
Remove Takes away a part of a material or information from its prefixed place Refine Reduces material or information such that only the desired elements
remain Branch
Distribute Causes material or information to break up
Import Brings in material or information from outside the system boundary Export Sends material or information outside the system boundary
Transport Moves material from one place to another Channel
Transmit Moves information from one place to another Couple Brings two or more materials or information together Connect
Mix Combines two materials or information into a single component Actuate Commences the flow of material or information in response to an
imported control signal
Regulate Adjusts the flow of material or information Control
Magni-tude
Change Adjusts the flow of material or information in a predetermined and fixed manner
Convert Convert Changes from one form of material or information in another one Store Accumulates material or information
Supply Provides material or information from storage Provision
Extract Draws a material or information Sense Perceives a signal
Indicate Makes something known to the user Display Shows a visual effect
Signal
Measure Determines the magnitude of a material or information flow Support Stop Ceases the transfer or material or information
Table 8: Basic Functions (cf. Stone and Wood 2000)181
The derivation of the sub-functions must be conducted for any input flow of the overall func-tion. Aggregating over all sub-function chains leads to the function structures. Note that these sub-functions are at the same level of complexity. As those resulting sub-functions can be too high-level to find solutions for them, they are further decomposed into sub-functions of de-creasing complexity, until the search for a solution seems promising (Hundal 1990).
Operation 3 – Distinction into Main and Auxiliary Functions
The last step of establishing the function structure distinguishes the sub-functions into main and auxiliary functions. Main functions directly affect the overall functions whereas auxiliary functions are complementary. While main functions are designed from the outset of concep-tual design, auxiliary functions are left aside until the embodiment design.
180 A conversion of the grammatical approach proposed here into a machine readable format is straightfor-wardly possible as Szykman et al. demonstrate (Szykman, Senfaute et al. 1999; Szykman, Bochenek et al. 2000)
181 The list of basic functions is reduced in comparison to the original source. The reason stems from the fact that some mechanical engineering functions are inapplicable for market engineering. Furthermore, the energy flow has been substituted by information. This information does, however, not correspond to con-trol information. The distinction into information and signals is still active.
The Function Structure of the Electronic Market Service
In market engineering the design object is the electronic market service. The function struc-ture can be derived following the abovementioned operations:
Operation 1 – Generate Black Box Model
Firstly, the overall function of an electronic market service must be defined. The specification representing the overall function of the electronic market consists of at least a verb-object combination – quantitative or qualitative statements can enhance the specification. Basically the simple electronic market service, which is depicted in Figure 24, constitutes the function of providing an efficient resource allocation process.
The inputs from outside (i.e. from the participating agents) are either information or material.
In our example case, it is assumed that the electronic market service accepts the physical transaction objects, and stores it until it is sold. Furthermore, the electronic market service requires information about the identity of the participating agents, their reputation and, of course their bids along the market process. Finally, the payment that the buyer pays to the seller is needed. As an output the service yields the allocation and prices, transfers the money to the seller, ships the transaction objects to their new owners, updates the reputation and ren-ders information about the market process, e.g. the bidding history.
Material Flow Information Flow Signal Flow
Provide efficient Resource Allocation
Process Reputation
Money
Trading Object Personal Data
Trading Object Allocation/Prices Money
Reputation
Bids Bidding History
Figure 24: Black Box Model for an Electronic Market Service
Stated differently the overall function of the electronic market service describes on a high level the service concept.
Operation 2 – Breaking down into sub-functions
The black box model clearly sketches a very crude picture of the electronic market service. As such, the overall function must be decomposed into sub-functions. The decomposition devel-ops for each input flow a chain of sub-functions that operate on that flow. For example, Figure 25 sketches the sub-function chain for the “bids” input flow. By analyzing the flow, the designer realizes that six operations are necessary before the bids are processed into allo-cations and prices and conveyed to the participating agents.