Databases Reference
In-Depth Information
Figure 14: Schema and an Instance of the Scene Database
The Shape of Individual Model can be effectively used as a mediator but it is
not feasible to create a mediator for every single object in the scene. However, the
role of the mediator proposed in this paper is to provide index for the original
data (shape data and pictures) when later querying the objects in the database.
Thus, for indexing by information not expressed by the mediators, another indexing
method is necessary. In our research, because with the original data the pictures
themselves are stored, too, for those objects without a mediator though it imposes
heavy computation costs at query time it is possible to use the pictures themselves
to construct a cyberworld, and at the same time realize the same degree of reality.
6
Design and evaluation of the scene database
In this section we describe the database design based on the Shape of Individual
Model and the movement information in the virtual space.
Figure 14 shows an example of the Shape of Individual Model mentioned in the
previous section and how its movement data (in time) is expressed in the database.
In the aforementioned scene database, the information (Shape of Fundamental
Model, Shape of Individual Model) about the objects participating in the scene,
the information about the location and the original sampled data (scanned shapes
and three-dimensional pictures) and other primitives need to have a structure in
which they are mutually and equally referring to each other. For this reason, it is
convenient to use a data model having a flat structure instead of special, hierarchical
structure. The relational model does have a flat structure and is capable of
expressing two-way relations, but it is incapable to store “order” expressively and
it is very difficult to use special operators graphic operators and picture operators,
etc. that are necessary to manipulate the scene database. Also, the object-oriented
model is based on a hierarchical structure, so it is suitable for handling graphics
