and (viewpoint value pedestrianLevel or viewpoint value birdsEyeView))))
and (informationType some (concept some wn:pollutant
and concept some wn:concentration and concept some wn:air))
In this case, the system will be able to retrieve, for instance, techniques that were
used to estimate the concentration of nitrogen oxide or sulfur dioxide in the air
(since these are subclasses of Pollutant ).
This type of query cannot be expressed in standard relational or xml databases
because they do not take into account the notion of subclass and the related infer-
5.2 Detection of Incompatibilities Between Techniques
From the rules that we have defined in SWRL, we inferred the potential incompat-
ibilities between all the techniques that we defined in the knowledge base. Here
are some (partial) results:
• A technique that displays soundscapes as texts on 2D interactive static panels
(see Fig. 8 for an illustration of such a technique) is potentially self compatible.
This means that it is possible to use several such panels within the same scene
(but not at the same place of course). Such a technique is also potentially com-
patible with a technique whose output rendering is defined by solids (such as
the technique illustrated in Fig. 9 ) and with a technique whose output rendering
is a texture, mapped on the terrain for example.
• A technique whose output rendering is a texture mapped on the terrain is self incom-
patible since occlusion is generated when several such techniques are used together.
• A technique whose output rendering is associated to a solid (e.g. a cone) is potentially
self incompatible (since it is difficult to distinguish which solids have been generated
by which technique) but such a technique is potentially compatible with a similar
technique whose rendering solid is of a different form (e.g. a cube or a sphere).
Detecting potential incompatibilities aims at assisting a designer who needs to
choose several visualization techniques among many techniques and to combine
them for visualizing information and data sets that have to be rendered together.
Of course the final decision belongs to the designer since he/she can estimate that,
for his/her particular set of data, such technique can be used in conjonction with
such other one, the potential incompatibility not occuring in this particular case.
6 Specification of an Environment for User Evaluation
The next step is to build a test environment in which the users can try several visu-
alization techniques on their own datasets and 3D scenes. We currently work on
a first design and implementation of this environment. The challenge is to create