Introduction - Human-Computer Interaction - page 13

plications of PPUIs. The following chapter will provide a comprehensive overview
of concepts and systems.

1.3 Challenges

The novel type of user interface that is made possible by digital pens creates con-
siderable challenges for interface design, since established paradigms for Graphical
User Interfaces (GUI) do not, or only partially, apply to this setting. This topic ad-
dresses the following challenges:

Appropriate Paper-based nteraction Techniques What are appropriate interac-
tion techniques for user interfaces that are printed on paper? Is it possible and de-
sirable to transfer established concepts from Graphical User Interfaces to PPUIs?
For instance, GUI dialogs including widgets such as buttons, checkboxes and text
input fields could be printed on paper. The pen could replace the mouse. Or is it
a more promising approach to take inspiration from the well-established practices
of working with paper? How could interaction techniques look like that take inspi-
ration from paper-based interactions? And finally, how can we make sure that the
novel interaction techniques fit into how we work with paper and how we work with
computers?

I

Restricted Feedback Capabilities Graphical User Interfaces allow the system to
provide extensive feedback to the user in real-time. In contrast, PPUIs have a re-
stricted feedback loop. Ideally, PPUIs could update the printed user interface in
real-time, similarly to how GUIs can update the user interface on the screen. How-
ever, current digital pens cannot print information on paper. Therefore, it would be
necessary to reprint the entire sheet of paper for updating information. So real-time
feedback, for instance about the system state, has to be given by other channels.
Current digital pens can provide only restricted feedback - most pens cannot pro-
vide any system feedback at all, and even the most advanced pens feature only a
very small display. Therefore, external devices, such as nearby screens, are typi-
cally used for this purpose. Yet, the key affordance of pen and paper is its mobility
and the fact that no other devices or tools are necessary during mobile use. To retain
this key affordance, interactions in a PPUI shall be reliable and clear even if only
very limited digital feedback can be provided.

Static vs. Dynamic User Interface This challenge is related to the previous one.
Content which is printed on a sheet of paper is static when compared to dynamically
updated information which is displayed on a screen. Hence a printed user interface
risks to be rather static. Nevertheless, the PPUI should be dynamic and flexibly
adapt to the current needs of the user.

Symbiotic Integration into Existing Practices PPUIs should symbiotically inte-
grate into existing and well-established work practices. One challenge is connected
to the implicit and highly personal way we use traditional pen and paper. As dis-