maintenance, and operation (Yuan, 1995). However,
how to define and to link the semantic object,
temporal objects and spatial objects and how to
reduce the redundancy of the (unchanged and
changed) data are not discussed in her paper.
Downward | Semantics Upward
arrows domain "i arrows
(Semantics- : (Location-
centered) = : centered):
Object- x : Layer-view
view Time : with/without
with/without time domain i time
modelling x : modeling
approach : : approach
Examples: ; Examples:
research on : research on
fire behaviour Space : fire forecast
fire effects domain | fire history
Figure 3: The three domains model (Yuan, 1995)
Peuquet (1995) set up a triad representation
framework illustrated in Figure 4. The object-based
representation includes four types of attributes, i.e.,
the generalized locational indicator, temporal
intervals, nonspatio-temporal data and higher-level
knowledge about known spatio-temporal
phenomena. In the event-based model, an event is
Stored as an observation in the time-based view.
Each event and the attributes describing it are
stored in their chronological order of occurrence.
The attributes might include the time of change, the
locations of change and types of objects. The
location-based representation is a raster based
snapshot. Some relationships exist among the data
in these three models, but how to organize the data
effectively to reduce the data redundancy is not
discussed in her paper. E.g., different events have
different objects, the location and nonspatio-
temporal description may be the same among
several objects.
Object-oriented
Representation
«c. NN
nd 2S
Location-based Time-based
Representation Representation
Figure 4: The triad representation framework
(adopted from Peugeut, 1995)
Furthermore, in the two models of Yuan and
Peuqeut the objects exist dependent on nonspatio-
temporal attributes. However, some objects at
different locations may share the same attributes
and the value of the nonspatio-temporal attributes
may changes at a specific location. So a Rich
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996
Spatio- Temporal Data Model (RSTDM) is proposed
(Roshannejad, 1996), wherein a object is uniquely
defined by its identifier (ID), which is the only
unchanged thing keeping the trace of the object.
The object is independent from their spatial and
attribute representations. While relationships
between objects and its spatial and nonspatial
attributes are recorded as another type of object. In
this way, the representations can be shared by
multiple objects so that a considerable amount of
space in the database can be saved. However, only
a few man-made objects have been implemented in
the RSTDM, such as building, roads and wells,
which changes suddenly and obviously. How to
adopt the model to natural phenomena with
irregular shape and gradual changes is not
discussed in the thesis. Moreover, the three
dimensional case is not discussed in the model.
4.3 The General Spatio-Temporal Data Model
The authors propose a general model, wherein an
abstract data type of object, unique and defined by
the user, is indicated by its identifier. All the
information related to the objects will be linked to it
through references.
There are two ways to build the temporal reference
of the spatial and nonspatial attributes to these
phenomena. One is to link the temporal reference
tightly (or explicitly to the spatial data and
nonspatial attribute data, i.e. when the object has
which kind of thematic attributes at which places
(see Figure 5(a)). Another way is to set up two
historic lists to show the relationships of the object
with its properties, i.e. one shows when the object
has which kind of thematic attributes, another one
shows when the object is where (see Figure 5 (b)).
In this case, the first level stores the information
about the objects, which can be managed by an
object-oriented database management system
(OODBMS); while the real content of the object, i.e.,
the location, the temporal information and
nonspatio-temporal characteristics as well as the
processes related to the objects are stored in the
second level, which can be maintained by an
OODBMS or a relational database management
system (RDBMS).
5. TOWARDS FULL INTEGRATION
The object-oriented approach discussed so far
concerns only how to describe the objects in a
spatio-temporal environment. More important, to
capture its development, is the major concern of
environmental models. If the objects can not only
carry the information on the spatial, temporal and
attribute characteristics of the environment, but also
its development, then we come close to the stage of
fully coupling the environmental models with GISs.
As discussed in Section 2, the objects can be
defined from the view point of application and the
users perspectives, e.g. from the behavior of the
phenomena, then such aim can be achieved.
