Databases Reference
In-Depth Information
An example of a category definition is given below, where a category of OA desks
is defined as a sub- category of category Desk. Note that an OA desk is a composite
object that consists of two parts, i.e., a topboard and legs which are defined in
category OA_desk_topboard and OA_desk_legs, respectively. As an example of
behaviors, a constructor is shown here, where the initial values of the topboard,
the legs, and the material of the legs are set using functions such as setvalue() and
setmaterial value(), respectively.
3.2.3
The VWDB Spatial Domain Definition Sub-Language
Spatial attributes need spatial domains to take on 3-D shapes as their values. In
general, 3-D shapes are created using a 3-D computer graphics software or CAD
software. However, such software describes a shape only as an instance. In other
words, they do not provide a schema-level description of 3-D shapes. One exception
is that the function “PROTO” defined in VRML allows a schema-level description
of a 3-D shape in the sense that an arbitrary 3-D shape can be created by specifying
a certain set of parameter values of a specified data type. For example, the next
statement shows how to define a domain of 3-D shapes like the tables shown in
Figure 4. The field statements specify a set of default values for the shape parameters.
To specify a desired shape of the “ta007” PROTO type, a certain set of parameter
values are specified in the constructor execution phase when a VWDB object is
created or updated.
4
The VWDB Multi-modal Database Language
4.1
Design Principles
In the VWDB, it seems natural to realize a multi-modal user interface for VWDB
users because users immerse themselves in the 3-D database space that is a virtual
synthesized world by wearing and using various pieces of equipment, such as an
HMD, a data glove, a 3-D mouse, a microphone, and sensors. To design a multi-
modal database language for the VWDB, we first investigated an entire multi-
modal interaction scheme in the VWDB, where the use of gestures and voice
