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Klaus Kespohl, Gerd Szwillus
Universit�t - GH Paderborn, FB 17
D-33095 Paderborn
+49 5251 60-6624
szwillus@uni-paderborn.de
Prototyping, formal specification, design techniques, development tools, usability testing, evaluation
We present the tool KAP (Kespohl's Automaton Prototyper) for prototyping user interfaces of technical devices, such as VCRs, CD players, alarm clocks, answering machines, etc. The work is based on a formal specification language, DSN/2. KAP supports this notation - as an editor, for adding interactive elements, and as an animation tool. The system was found suitable for performing user tests on several software models, including a CD player with realistic functionality; the results were verified against user testing on the real device.
With our demonstration we show that and how it is feasible to create realistic prototypes with the tool. We create the simulation of a CD player on-line while people are watching. We start with a photograph and the instructions manual of the CD player and then stepwise develop the KAP model of this device. We demonstrate how the model is working, thus proving its potential for user-testing. The audience observes how we start from an abstract control model specification, stepwise add information, and finally come up with a running prototype.
Electronic devices known as "end-user programmable devices" today are more wide-spread than ever. Electronic clocks, telephones, answering machines, calculators, VCRs, or CD players, come with sophisticated functionality brought to the human user through computer-based device interfaces. We all know that it can be very hard to control these devices, and that a considerable percentage of their owners is not able to exploit all functions, giving up at the sight of numerous buttons and a voluminous user's manual. The externally experienced behaviour of a device can be described as a sequence of "situations", with a situation being given in terms of the visible appearance, the sounds produced, and the input possibilities provided. The sequence of the situations is governed by rules based on the actions performed by the user and the device. Expressed in this terminology, the most severe problems human users experience stem from controlling the situation sequences, rather than from understanding the single functionalities of a device. In computer science terms the user has to "understand" a potentially large, finite automaton with attached functionality - the system's control model. The user of a device must build an internal model matching the control model of the device.
We propose a technique for specifying the control model of a device with the abstract specification language DSN/2. This language is based on the concept of states and state transitions; it is written in a notation called DSN/2, which is based on the Dialogue Specification Notation (DSN) [1,2], which in turn has its roots in the Propositional Production System (PPS) [7].
DSN/2 is used by the interface designer to define the control model of a user interface. Developing such a specification necessitates the possibility to "see how it works" to verify the correctness of its behaviour. The MS Windows� tool KAP, presented in this demonstration session, supports the work with DSN/2. With KAP, a designer can create a realistic prototype of device user interfaces. It looks like the real thing, it produces the same sounds, and its state behaviour can be observed and tested. Adding the animation does only necessitate experience in using MS Windows�-style programs, hence it can be mastered by non-programmers. Roughly speaking, KAP's features are editing facilities for DSN/2 specifications, generating default animations, and specifying individual visual and acoustic animations.
The language DSN/2 itself does not include information about the visual appearance or acoustic feedback of the user interface. Hence, the simplest animation of the control model possible is defined in terms of the language elements of the DSN/2 specification. KAP provides two default animations on this level, a textual animation [3] and a graphical default animation. Both exist without any additional effort for every DSN/2 model loaded into KAP and both are not intended for user testing, but as tools for the user interface designer, working on the DSN/2 model.
The
elements of the graphical default animation can subsequently interactively
be moved, resized, hidden, and replaced by externally defined bitmaps (drawings
or scanned photographs). One can link different pictures to different states
to visualize state transitions through lights turning on and off, changing
colours, or displays showing different symbols. The input behaviour can
be changed to model small key matrices, toggle buttons, repeat keys, sliders,
or similar devices. With these modifications we could model several devices
very realisticly. For instance, the graphical animation of the simulated
CD player shown above strongly resembles the original. As sound carries
important feedback clues for the user, we included the possibility to link
sounds to the raising of flags. This can be done interactively in the KAP
tool or in the DSN/2 specification by inclusion of sound annotations.
We think that KAP has significant advantages over environments such as HyperCard� or SuperCard� [5] typically used for prototyping purposes, as they necessitate programming expertise. The same argument applies to prototyping done with environments like VisualBasic�. An interface designer working with KAP must only be familiar with the concepts of state and rule-based state transition. These, however, are central design issues anyway, so only the notation has to be learned. Other tools such as GARNET [6] and its successors, Whizz'Ed [4], or our own approach OBJECTION [8] urge the designer to familiarize with additional concepts such as constraints or data-flow specifications. These are too much influenced from a programming style of user interface development for being applicable by non-programming interface designers.