6 System Status
Work on Delta-X is still in progress towards im-
plementing a full functional system. Our cur-
rent prototype, operates with three DzServer sys-
tems: two relational database management sys-
tems that execute SQL queries, Ingres and Or-
acle, and one simple file system. Several GISs
run DxClients that interact with these servers.
The frontend, GUI, of Delta-X is completed. The
first level display window on invoking Delta-X is
showm in Figure 3. Figure 4 shows the display of
a vector map from a remote server. The imple-
mented systems rely purely on remote procedure
calls for its remote operations.
The Delta-X project began before serious ini-
tiatives with respect to standards for interoper-
ability between commercial relational databases
were fully specified. Work on standards for in-
teroperability in object-oriented database is still
ongoing and for standards for interoperability
between multi-databases is yet to be drafted.
We have since identified close similarity between
the multi-database requirements in Delta-X the
functional services provide by the Xopen refer-
ence model for distributed transaction systems.
We are exploring the use of a commercial dis-
tributed transaction that meets existing interna-
tional standard and satisfies our current opera-
tional functions. This, we believe, can be easily
adopted to reduce our development time for the
multi-database transaction modules of our sys-
tem.
7 Conclusion
The Delta-X operational paradigms describe
a methodology for the integration of multi-
database management concepts and data inter-
change in a network of heterogenoeus databases.
The system as designed is a sufficiently open sys-
tem that freely admits new participants, either
as new databases management systems or new
GIS technology, with minimum overhead. The
only essential requirement is that new database or
GIS vendors must provide the mapping functions
that translate information between their propria-
tory data format and our global conceptual data
model.
We have described the essential functionalities
in Delta-X and we have shown the software mod-
ules required to be integrated to achieve a suc-
cessfull implementation. GIS database develop-
ment is an exercise being carried out as national
projects in several countries. We believe the ap-
proach taken by the Delta-X design will form the
reference model by which similar projects will
emerge to establish eventually, a global network
of GIS databases.
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