ee oz oO 
e in the 
ollowing 
spatial 
Current data: (ID, ..., Ts, Lh) 
History data: (ID, ..., Ts, Te, Lh, Lf, NumofSon) 
Future index: (ID, L) 
Where '...' stands for attributes of the land parcel. Lh 
is record number of its 'parents' in history database. 
And Lf is the record number of its son's index in 
future index database. Since records in the current 
database would be deleted when they became history, 
we need L to maintain the correct linkage. NumofSon 
shows how many sons it has. All sons' index are 
recorded sequentially in the future index database. In 
decomposition, NumofSon is greater than 1; but in 
consolidating , NumofSon is 1. 
According to this definition, we can get Tables 
describing the process of land subdivision in Fig.1 
at the time Tnow. 
From Table 5, we know that temporal land parcel 
P1001 was valid from 1949 to 1977, its parent is not 
recorded in the temporal database (Lh - 0). And 
P1001 decomposed into P1002 and P1003, which are 
the first (Lf = 1) and second record in Table 4. 
Furthermore, we can read that P1003 is the fourth 
record in history database. 
Also, we know P1008 is an active object with no 
ending time and no future at Tnow. From Lh = 4, we 
track its history P1004, the fourth record in Table 5. 
Since P1004's NumofSon equals 1, P1008 is 
consolidated from several parcels. So Lf of the fifth 
record, the next record of P1004, is compared with 
that of P1004. Because they both equal 7, then the 
fifth record (P1006) is also P1008's history. 
Generally speaking, with the three databases, the 
spatio-temporal information concerning the land 
subdivision could be referenced. 
4.3 Organize Spatial and Aspatial Attributes 
in the Extended Space-Time Composite 
In the process of land subdivision, a parcel changes 
its ID only when its geometry changes. So time in 
attribute-level can be considered at two levels; at the 
attribute value level and at the tuple level. Times at 
tuple level, the first level, defining the geometric and 
static thematic states of land parcels, while time at 
attribute value level, the second level, representing 
the dynamic thematic states of land parcels. In order 
to reference a temporal land parcel, tuple level is 
firstly located, then the attribute value level. 
55 
5. SUMMARY 
It has been becoming crucial for more and more GIS 
application projects now to add time dimension in 
GISs and make temporal data accessible to users 
[Gagnon, et.al; 1992; Langran, 1993b; Al-Taha, et.al. 
1994]. In the case of land subdivision, one of the 
fundamental issues is to develop a descriptive 
formalism for the time-related spatial phenomena 
which can be used to help specify and structure 
spatial-temporal databases. The space-time 
composite model proposed by Langran was 
extended in this paper by defining and representing 
temporal objects and active objects. Further 
development and implementation of the extended 
space-time composite model for land subdivision is 
current under investigation by the author's research 
group at LIESMARS. 
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