m 
original 
imposed 
loys the 
id in the 
Langran, 
d P1007 
temporal 
1992 and 
xamples, 
discrete 
te model. 
s of the 
ed and 
rst of all, 
2, P1003, 
irst time 
y were 
sition or 
in Thow 
e spatio- 
n. The 
thematic 
1 should 
function. 
ould also 
d-related 
gregated 
temporal 
unit according to the underlying principle of the 
space-time composite model. For instance, P1008 is 
one object from the point view of land subdivision; 
but it is described by P1004 and P1006. Hence, P1008 
is not a common unit and can not be represented 
directly in the space-time composite. In fact, the 
parcels could not only be carved into smaller 
segments during the process of land subdivision, 
but also be consolidated or aggregated into larger 
parcels. Because in real world, people does regard 
the consolidated parcel as one object, not the 
smaller fragments which making up of it. 
In order to solve the above problems, we propose to 
extend the space-time composite model by defining 
and distinguishing temporal objects and active 
objects, inspired by the temporal concept of Elmasri 
et. al(1993). A temporal object in our extended space- 
time composite model has its specific lifespan and 
should be referenced at any future time once it is 
created. An active object is an active temporal object 
who has specific starting time and has no ending 
time. According to this definition, P1001, P1002, 
P1003, P1004, P1005, P1006, P1007 and P1008 are all 
  
  
  
  
temporal objects and should be maintained as 
database objects. At the time Tnow, P1005, P1007 
and P1008 are active temporal objects who have no 
ending time, while P1001, P1002, P1003, P1004 and 
P1006 are non-active temporal objects with specific 
ending times. The relationship between temporal 
objects and active objects in the extended space- 
time composite model is shown in Fig.2. XY in Fig.2 
represent the x, y coordinates of the nodes and 
edges. Each land parcel that ever existing is 
database object represented in the extented spatio- 
temporal composite. Table 1 lists all the temporal 
parcel objects which need to be referenced in the 
extended space-time composite model. In addition, 
some relationships between these parcel objects 
need to be modeled which would reflect the land 
subdivision path. For instance, each time a land 
parcel is splited into two parcels with new identifies 
and distinct geometric components, there do exist a 
casual relation between the old parcel and the two 
new parcels. Modeling such casual relation will allow 
us to track the history of the subdivision of one 
parcel or track the parents of one new parcel. 
Parcel br Attribute 
  
Active Parcel 
Active Attribute 
  
  
  
<Q 
  
  
  
  
  
Edge  [4——9| Active Edge 
  
  
  
  
Ed 
  
  
$ 
  
  
Node 4 
  
  
Active Node 
    
  
  
  
  
> 
AD non-active object 
XY 
  
  
  
[ | active object 
  
C ER relation 
Figure.2 Temporal objects in Extended Space-Time Model 
1992 10 
  
Fig.3 Further evolution of Parcel P1007 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996