What do Prototypes Prototype? Stephanie Houde and Charles Hill Apple Computer, Inc. Cupertino, CA, USA [email protected], [email protected] 1. INTRODUCTION the kinds of prototypes to build. With a clear pur- Prototypes are widely recognized to be a core means pose for each prototype, we can better use proto- of exploring and expressing designs for interactive types to think and communicate about design. computer artifacts. It is common practice to build prototypes in order to represent different states of In the first section we describe some current diffi- an evolving design, and to explore options. How- culties in communicating about prototypes: the ever, since interactive systems are complex, it may complexity of interactive systems; issues of multi- be difficult or impossible to create prototypes of a disciplinary teamwork; and the audiences of pro- whole design in the formative stages of a project. totypes. Next, we introduce the model and illus- Choosing the right kind of more focused prototype trate it with some initial examples of prototypes to build is an art in itself, and communicating its from real projects. In the following section we limited purposes to its various audiences is a criti- present several more examples to illustrate some cal aspect of its use. further issues. We conclude the chapter with a sum- mary of the main implications of the model for The ways that we talk, and even think about pro- prototyping practice. totypes, can get in the way of their effective use. Current terminology for describing prototypes cen- 2. THE PROBLEM WITH PROTOTYPES ters on attributes of prototypes themselves, such as Interactive computer systems are complex. Any what tool was used to create them, and how re- artifact can have a rich variety of software, hard- fined-looking or -behaving they are. Such terms ware, auditory, visual, and interactive features. For can be distracting. Tools can be used in many dif- example, a personal digital assistant such as the ferent ways, and detail is not a sure indicator of Apple Newton has an operating system, a hard case completeness. with various ports, a graphical user interface and audio feedback. Users experience the combined We propose a change in the language used to talk effect of such interrelated features; and the task of about prototypes, to focus more attention on fun- designing—and prototyping—the user experience damental questions about the interactive system is therefore complex. Every aspect of the system being designed: What role will the artifact play in must be designed (or inherited from a previous sys- a user’s life? How should it look and feel? How tem), and many features need to be evaluated in should it be implemented? The goal of this chapter combination with others. is to establish a model that describes any prototype in terms of the artifact being designed, rather than Prototypes provide the means for examining de- the prototype’s incidental attributes. By focusing sign problems and evaluating solutions. Selecting on the purpose of the prototype—that is, on what the focus of a prototype is the art of identifying the it prototypes—we can make better decisions about most important open design questions. If the arti- fact is to provide new functionality for users—and This article is published, in a different format, as Houde, S., thus play a new role in their lives—the most im- and Hill, C., What Do Prototypes Prototype?, in Handbook of portant questions may concern exactly what that Human-Computer Interaction (2nd Ed.), M. Helander, T.␣ Landauer, and P. Prabhu (eds.): Elsevier Science B. V: role should be and what features are needed to sup- Amsterdam, 1997. port it. If the role is well understood, but the goal 1 of the artifact is to present its functionality in a which shows a scenario of something being used, a novel way, then prototyping must focus on how prototype. the artifact will look and feel. If the artifact’s func- tionality is to be based on a new technique, ques- The organization supporting a design project may tions of how to implement the design may be the have an overly narrow expectation of what a pro- focus of prototyping efforts. totype is. Shrage (1996) has shown that organiza- tions develop their own “prototyping cultures” Once a prototype has been created, there are sev- which may cause them to consider only certain kinds eral distinct audiences that designers discuss pro- of prototypes to be valid. In some organizations, totypes with. They are: the intended users of the only prototypes which act as proof that an artifact artifact being designed; their design teams; and the can be produced are respected. In others, only supporting organizations that they work within highly detailed representations of look and feel are (Erickson, 1995). Designers evaluate their options well understood. with their own team by critiquing prototypes of alternate design directions. They show prototypes Is a brick a prototype? The answer depends on to users to get feedback on evolving designs. They how it is used. If it is used to represent the weight show prototypes to their supporting organizations and scale of some future artifact, then it certainly (such as project managers, business clients, or pro- is: it prototypes the weight and scale of the artifact. fessors) to indicate progress and direction. This example shows that prototypes are not neces- sarily self-explanatory. What is significant is not It is difficult for designers to communicate clearly what media or tools were are used to create them, about prototypes to such a broad audience. It is but how they are used by a designer to explore or challenging to build prototypes which produce feed- demonstrate some aspect of the future artifact. back from users on the most important design ques- tions. Even communication among designers re- 2.2 Current terminology quires effort due to differing perspectives in a multi- Current ways of talking about prototypes tend to disciplinary design team. Limited understanding focus on attributes of the prototype itself, such as of design practice on the part of supporting orga- which tool was used to create it (as in “C”, “Direc- nizations makes it hard for designers to explain their tor™”, and “paper” prototypes); and on how fin- prototypes to them. Finally, prototypes are not self- ished-looking or -behaving a prototype is (as in explanatory: looks can be deceiving. Clarifying “high-fidelity” and “low-fidelity” prototypes). Such what aspects of a prototype correspond to the even- characterizations can be misleading because the ca- tual artifact—and what don’t—is a key part of suc- pabilities and possible uses of tools are often mis- cessful prototyping. understood and the significance of the level of fin- ish is often unclear, particularly to non-designers. 2.1 What is a prototype? Designing interactive systems demands collabo- Tools can be used in many different ways. Some- ration between designers of many different dis- times tools which have high-level scripting lan- ciplines (Kim, 1990). For example, a project might guages (like HyperCard™), rather than full pro- require the skills of a programmer, an interaction gramming languages (like C), are thought to be designer, an industrial designer, and a project man- unsuitable for producing user-testable prototypes. ager. Even the term “prototype” is likely to be However, Ehn and Kyng (1991) have shown that ambiguous on such a team. Everyone has a even prototypes made of cardboard are very useful different expectation of what a prototype is. for user testing. In the authors’ experience, no one Industrial designers call a molded foam model a tool supports iterative design work in all of the im- prototype. Interaction designers refer to a simula- portant areas of investigation. To design well, de- tion of on-screen appearance and behavior as a pro- signers must be willing to use different tools for totype. Programmers call a test program a proto- different prototyping tasks; and to team up with type. A user studies expert may call a storyboard, other people with complementary skills. 2 Finished-looking (or -behaving) prototypes are of- Role ten thought to indicate that the design they repre- sent is near completion. Although this may some- times be the case, a finished-looking prototype might be made early in the design process (e.g., a 3D concept model for use in market research), and a rough one might be made later on (e.g., to em- phasize overall structure rather than visual details in a user test). Two related terms are used in this Implementation context: “resolution” and “fidelity”. We interpret resolution to mean “amount of detail”, and fidel- Look and feel ity to mean “closeness to the eventual design”. It is Figure 1. A model of what prototypes prototype. important to recognize that the degree of visual and behavioral refinement of a prototype does not nec- essarily correspond to the solidity of the design, or inherently more important than any other. to a particular stage in the process. 3. A MODEL OF WHAT PROTOTYPES PROTOTYPE Goal of the model 3.1 Definitions Given a design problem (of any scope or size), de- Before proceeding, we define some important terms. signers can use the model to separate design issues We define artifact as the interactive system being into three classes of questions which frequently de- designed. An artifact may be a commercially re- mand different approaches to prototyping. Imple- leased product or any end-result of a design activ- mentation usually requires a working system to be ity such as a concept system developed for research built; look and feel requires the concrete user ex- purposes.