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the designers to provide useful functionality, but the local participants complete the
job by integrating them into their practices in a way that makes sense for them.
In summary, we derive the following implications for the design of Pen-and-
Paper User Interfaces. First, the design should consider collaboration as a key aspect
in document work. Second it should take the interdependencies between multiple
(physical and digital) documents and (physical and digital) tools seriously into ac-
count. Third, detailed analysis of the ecology which to design for is crucial. Fourth,
end-users adapt novel technology to fit into existing ecologies. Technological tools
should be generic enough such that end-users can easily localize them. This general
perspective allows us to address in the following more closely how interactions with
Pen-and-Paper User Interfaces can be modeled.
3.4 Model of Interactions
Pen-and-Paper User Interfaces have other characteristics than Graphical User Inter-
faces (GUI), because they comprise physical objects as interface elements and use
a digital pen as the main interaction device. In contrast, GUIs typically rely on key-
boards and mice. Moreover, paper is a very restricted output channel, which makes
it challenging to design a user interface that supports complex activities and still
remains easy to use. This implies that it is not sufficient to transfer interface ele-
ments from the GUI to paper, such as transferring text input fields or buttons. We
argue that instead, interactions should build upon specific paper affordances, such
as simultaneously using multiple pages.
In this section, we present a model of pen-and-paper-based interaction which
provides guidance for analysis and design of interfaces. The underlying principle
of the model is an analytic separation of interaction into a semantic and a syntactic
level (see Fig. 3.6):
1. The semantic level models
what
the user wants to do and comprises conceptual
activities, i.e. the functionality offered by the user interface (for instance the ac-
tivities of annotating, linking and tagging).
2. The syntactic level models
how
the user actually performs these activities. It
comprises core interactions, i.e. primitive manipulations that are made with the
PPUI in order to actually perform these conceptual activities (e.g. writing with
the pen or attaching a paper sticker).
2
The challenge when designing a PPUI is first to identify simple and reliable core
interactions which leverage the affordances of pen and paper. Second, the designer
must decide which core interactions to use and how the user combines them to
2
This separation of interaction into two levels is conceptually similar to the four-level model by
Foley et al. [30]. In addition to the semantic and syntactic levels, this covers a conceptual level,
which is the user's mental model of the interactive system, and a lexical level, which encompasses
the precise mechanisms by which the user specifies the syntax. We judge two levels to be sufficient
for our aim of identifying core interactions and of modeling how these can be composed.
