Information Technology Reference
In-Depth Information
Thus, the KUP model is different from classical models (ARCH, Seeheim, PAC,
MVC, etc.) due to the fact that in the latter the user is always outside the system; he
is never explicitly represented as an active entity. In the KUP model the user entity
U is the central entity; see Figure 10.2.
10.4.3.
Notion of proximity
In order to construct an opportunistic system based on meetings between entities,
we need to formally define the corresponding notions of
proximity
.
10.4.3.1.
Perceptual space
Informally, we wish to define the
perceptual space
of a physical entity
e
as
being the collection of points in space where
e
can perceive another entity that is
present. For example, for a user entity the perceptual space could correspond to its
visual field. However, this definition is too restrictive because:
- The different senses of a user have different characteristics. For example, the
field of vision of a human being does not correspond to their zone of auditory
perception. Thus, a screen situated 2 m behind will not be perceived by a given user,
whereas a speaker device will be.
- Perception depends on the
attributes of modalities.
For example, a cell phone
ring tone emitted at 50 m will not be perceived by a human being, whereas the
sound of a siren will easily be.
Consequently, the informal definition of the notion of perceptual space given
beforehand is too limited. It must be completed to take into account modalities and
instantiations of the latter. To do this, we introduce an additional notion:
multimodal
space
,
or m-space for short. An m-space is the Cartesian multiplication of the
physical space
E
by all the instantiations of usable modalities. For example, let us
assume that the usable modalities for an entity are:
-
ringtone
, with a
volume
attribute continuously varying between 0 and 100;
-
text
, with a
size
attribute continuously varying between 10 and 60 points and a
color
attribute that can take the three discrete values of
red
,
green
and
blue
.
In this case, an element of the m-space could be the point that has coordinates of
46°23''32' N, 1°02''56' E, with a point size of 23 for text and the color green.
It is now possible to formally define the
perceptual space
of a physical entity. It
consists of a subset of an m-space M, which corresponds to the
points
perceivable to
the entity. If the entity moves, its perceptual space will be modified: in most cases, it
will naturally
follow
its entity.
