In this position paper, the ambiguity of functional descriptions in engineering is considered from a methodological point of view. Four responses to this ambiguity are discussed, ranging from defining a single meaning of function and rejecting the different meanings that are currently used in engineering to accepting these meanings as coexisting in engineering and taking function as a family resemblance concept. Rejecting the different meanings is described as the straightforward response to resolving the ambiguity of functional descriptions, yet in engineering research and design methodology it rather seems to be accepted that engineers do use the coexisting meanings side by side. In this paper, explanations are given of why this practice is beneficial to engineering. Then it is explored how the particular meaning that engineers attach to function depends on the tasks for which functional descriptions are used. Finally, the methodological implications of the four responses to the ambiguity of functional descriptions are discussed.

Research on design and analysis of complex systems has led to many functional representations with several meanings of function. This work on conceptual design uses a family of representations called structure–behavior–function (SBF) models. The SBF family ranges from behavior–function models of abstract design patterns to drawing–shape–SBF models that couple SBF models with visuospatial knowledge of technological systems. Development of SBF modeling is an instance of cognitively oriented artificial intelligence research that seeks to understand human cognition and build intelligent agents for addressing complex tasks such as design. This paper first traces the development of SBF modeling as our perspective on design evolved from that of problem solving to that of memory and learning. Next, the development of SBF modeling as a case study is used to abstract some of the core principles of an artificial intelligence methodology for functional modeling. Finally, some implications of the artificial intelligence methodology for different meanings of function are examined.

Functional modeling is a very significant part of many different well-known design methodologies. This paper investigates the questions of what functional modeling approaches people use in industry and how they conceptualize functions. Using interviews and the findings from an experiment where 20 individual designers were asked to generate a functional model of a product, the paper highlights the different notions designers associate with the word function. Difficulties associated with functional modeling arise from varied and inconsistent notions of functions as well as wider challenges associated with modeling and the introduction of methods in industry.

The concept of a function is of great importance in design. This paper describes from theory how designers should reason about functions when designing. This paper introduces the link model, showing how functions and properties link the product and its use, to the perceived value of the product. The important and useful distinction between functions and properties is made along with the distinction between “wirk functions,” which is what the product does when operating, and “use functions,” which is what the product is used for. The paper makes a novel contribution beyond previous literature, showing that not only is a product's behavior or mode of action designed but also the use activity of the end user. Based on the theoretical perspective unfolded, the authors offer nine mind-sets for both design practitioners and researchers to consider when reasoning about functions.

Function is an ambiguous concept, whereas having explicit and precise concepts is critical for building a systematic science of engineering design. Based on Bunge's scientific ontology, this paper is devoted to developing an explicit and precise concept of function for design science. First, we attempt to clarify the concept of behavior, which is closely related to function and is also shown as an ambiguous concept in engineering. Second, the concept of action is imported from scientific ontology into design science. Third, a scientific ontology based concept of function is proposed, together with an ontology-based functional taxonomy. A case of a function definition of a civil aircraft type demonstrates that the proposed concept of function is more explicit and precise than previous ones, and it can lead to better functional design results.

Understanding product functions is a key aspect of the work undertaken by engineers involved in complex system design. The support offered to these engineers by existing modeling tools such as the function tree and the function structure is limited because they are not intuitive and do not scale well to deal with real-world engineering problems. A research collaboration between two universities and a major power system company in the aerospace domain has allowed the authors to further develop a method for function analysis known as function analysis diagram that was already in use by line engineers. The capability to generate and edit these diagrams was implemented in the Decision Rationale editor, a software tool for capturing design rationale. This article presents the intended benefits of the method and justifies them using an engineering case study. The results of the research have shown that the function analysis diagram method has a simple notation, permits the modeling of product functions together with structure, allows the generation of rich and accurate descriptions of product functionality, is useful to work with variant and adaptive design tasks, and can coexist with other functional modeling methods.

The authors have been involved in ontological modeling of function for over 15 years. As an instance of the revisionary approach discussed in Vermaas's position paper, we have proposed an ontological definition of function and a modeling framework based on it, which has been deployed in industry. In addition, as an instance of the overarching approach, we have proposed a reference ontology of function that explains some kinds, definitions, and practical expressions of functions. In this paper, we explain our methodology in an overarching approach based on perspectives for capturing functions. When one captures a function of an artifact, one focuses on a specific aspect of the artifact from a specific perspective. In this paper, we conceptualize such perspectives behind the reference ontology. In addition, based on our experiences in deployment in an industrial setting, we report some solutions, such as ontological modeling guidelines, for overcoming some of the difficulties faced in the practical functional modeling approach described in Eckert's position paper. Our findings suggest that such solutions will help engineers to describe consistent functional models compliant with a single definition of function.

Functions are important in designing. However, several issues hinder progress with the understanding and usage of functions: lack of a clear and overarching definition of function, lack of overall justifications for the inevitability of the multiple views of function, and scarcity of systematic attempts to relate these views with one another. To help resolve these, the objectives of this research are to propose a common definition of function that underlies the multiple views in literature and to identify and validate the views of function that are logically justified to be present in designing. Function is defined as a change intended by designers between two scenarios: before and after the introduction of the design. A framework is proposed that comprises the above definition of function and an empirically validated model of designing, extended generate, evaluate, modify, and select of state-change, and an action, part, phenomenon, input, organ, and effect model of causality (Known as GEMS of SAPPhIRE), comprising the views of activity, outcome, requirement–solution–information, and system–environment. The framework is used to identify the logically possible views of function in the context of designing and is validated by comparing these with the views of function in the literature. Describing the different views of function using the proposed framework should enable comparisons and determine relationships among the various views, leading to better understanding and usage of functions in designing.

Authors across disciplines propose functional modeling as part of systematic design approaches, in order to support and guide designers during conceptual design. The presented research aims at contributing to a better understanding of the diverse functional modeling approaches proposed across disciplines. The article presents a literature review of 41 modeling approaches from a variety of disciplines. The analysis focuses on what is addressed by functional modeling at which point in the proposed conceptual design process (i.e., in which sequence). The gained insights lead to the identification of specific needs and opportunities, which could support the development of an integrated functional modeling approach. The findings suggest that there is no such shared sequence for functional modeling across disciplines. However, a shared functional modeling perspective has been identified across all reviewed disciplines, which could serve as a common basis for the development of an integrated functional modeling approach.

Function-based design and modeling have been taught, studied, and practiced in various forms for several years with efforts centered on using function modeling to help designers understand problems or to facilitate idea generation. Only limited focus has been placed on potential use for qualitative and quantitative reasoning and analysis of the design concept. This potential for early stage analysis has not been fully explored partly because computational reasoning tools have not been developed for this express purpose. This paper presents a set of requirements and their justification to realize this design enabling tool. The requirements include coverage, consistency, validity against physics laws, domain neutrality, physics-based definitions, normative and descriptive modeling, and qualitative and quantitative modeling and reasoning. Each requirement is defined in concrete terms and illustrated with examples and logic. With the requirements for function-based reasoning and representation clearly identified, future research toward formalizing of function-based design will be more focused and objective validation of proposed representations against these requirements would be possible.

Function modeling is considered potentially useful in various fields of engineering, including engineering design. However, a close look at practices reveals that practitioners do not use formal function modeling so much, while the concept of “function” frequently appears in many practical methods without a vigorous definition. This paper tries to understand why formal function modeling is not practically utilized in industry by analyzing usage cases of function. By observing product development activities in industry, the paper identifies three problems that prevent formal function modeling from wider applications in practices, namely, practitioners' neglect of function modeling, the lack of practically useful function reasoning, and the complexity of the methods and tools of formal function modeling that make them impractical. Finally, the paper proposes strategies to tackle these problems and illustrates some research efforts in this regard.