On the Distinction Between Design Parameters and Functional Requirements
Authors: Fauvel Owen R. 
Published: March 2021

The working of the design process has been described as a process of mapping Functional Requirements into Design Parameters. The definitions of these two types of information appear to be based upon intuitive differences. It is posited that by generating an operational distinction between the attributes in these two information domains, useful information patterns can be described for use in the design process.

The following distinction is observed: whereas Design Parameters are deemed to have meaning which is insensitive to context, Functional Requirements and attributes can only be assessed with reference to the operative context or environment within which the designed object exists. Functional attributes such as usability, manufacturability, serviceability, safety, and affordability are seen not as intrinsic properties of a designed object but rather as measures of the interaction between the designed object and the relevant context; for the attributes cited, it would be necessary to characterize in turn the user environment, the manufacturing infrastructure, the servicing facilities and skills, the operational/legal environment, and the economic situation.

The distinction as outlined serves as a premise upon which a fundamental information structure can be based. The proposed structure involves the categorization of design information into not only the Function Domain and the Design Parameter domain but also embraces a third - contextual - domain identified herein as the Environment Domain. Operational definitions have been devised for each type of information. These definitions also point to the nature of the interactions between the three types of information which take place during the process of design.

It is suggested that what is presented here is not a new design paradigm but rather a new way to describe in a clear and explicit fashion the information and information transactions which are known to constitute the design processes. As such, it is seen to be of particular value in design education. However, it may also prove to be useful in organizing information systems for concurrent design activities.

This view of design information has emerged through efforts to improve the effectiveness of teaching both design and manufacturing courses as well as the desire to improve the management of graduate design projects. Additionally, it has been influenced through ongoing research and development in the design of specific mechanical systems. As such, it is firmly rooted in the practicalities of design and design teaching and is constantly being put to the tests of utility, practicality, and veracity. For example, assessment of the attribute “manufacturability” has led to a systematic structuring of knowledge and information about manufacturing infrastructure in a way which facilitates decision-making as well as explanation and justification of the decision-making process. Some progress is also being made in developing information patterns which embrace all three information domains by way of providing pre-packaged design solutions for well-established types of design problem. The “bolted-joint”, for example, represents an extremely common design element about which much can be determined analytically but about which many other functional aspects are less accessible. Manufacturability, serviceability, reliability are attributes which can be assessed when due consideration is given to context regarding manufacture, use, placement, etc.

The use of this information structure has also been useful in examining various models of the design process whether along traditional problem-solving lines or using artificial intelligence oriented systems. This approach has been used in examining the design process at the graduate level but student feedback has been sufficiently strong to suggest that it would be useful at the undergraduate level. In particular, while the traditional approach to teaching design provides an “activity map”, the addition of an “information map” is seen to be highly complementary.

The notion of the information map is also seen to be useful for the management of concurrent design endeavours. It would be expected to provide a picture of both communication pathways and indicate the nature of the communications required. For example, the attribute “affordability” will usually be of particular importance for most designed things. Assessment of this attribute requires knowledge of the marketplace as well as the cost of the article and its performance capability. The cost attribute will require knowledge of the manufacturability of the article and hence the capability of the manufacturing infrastructure. In this way diverse interests can be visibly linked. And of course the map need not be a static one but would be expected to reflect the dynamics of the design process.

If the distinction between attribute types continues to prove a useful and valid one, the door is opened to a new generation of parameterized design within which not only geometric relationships are programmed but more fuzzily-defined functions are determined by propagation of information along function-oriented pathways. The language for communication between disparate role-players in the design process has far to grow but the form of the communication can start to take on shape.

Finally, the proposed information map will provide an explicit history of a design project thereby facilitating such activities as design audits and accident investigations. Perhaps as important is the role of the information map in recording the knowledge of expert designers and the generation of case histories which more explicitly illustrate the role of specific pieces of information in the generation of design solutions.