International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
announced when this happens, which will lead to
difficult to access the changed format of the database
for data integration. If each GIS software package must
interoperate with any GIS spatial database, interface
functions to read/write different all their different
formats must be developed, which is a vast body of
work for developing the software package. If the API
function can be implemented, data can be accessed
directly, which will decrease the efforts of software
development. Figure 1 shows the interoperability based
on the direct access mode.
Figure 1 Interoperability Based on Direct Access to Databases
2.3 Interoperability Based on a Common Interface
If GIS software manufacturers develop modules to
access spatial databases according to the interface
specification constituted by international
standardization organizations (such as ISO/TC211) or
technical consortiums (such as OGC), heterogeneous
spatial database interoperability can be realized. With
regard to this interoperability in a distributed
environment, the spatial data interoperability
specification can be classified into two levels.
The first level is the API based on COM or CORBA
standards or the interface specification of SQL. By
constituting the common interface function form and
parameters, different GIS software packages can
directly access each other's database. This can be
implemented in two ways. The first is one in which the
data access interface of a GIS directly uses the
standardized interface function. The second way is one
in which a GIS has defined its own data access function.
So as to realize interoperability, it wraps a standardized
interface function on its own internal data access
function. The interface based on API uses binary data
with high efficiency, but is more complicated and
difficult to implement. Figure 2 shows the relationship
of specification interfaces for spatial data
interoperability based on API.
Common
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Figure 2 Relationship of Specification Interfaces for Spatial
Data Interoperability Based on API
If middleware technology of CORBA or J2EE is
adopted, interoperability based on common API can be
realized on the Internet, and a triple level architecture
or multi-level architecture can be easily constructed.
The implementation method is similar to the previous
one with additional middleware, as Figure 3 illustrates.
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Figure 3 Interface Relationship of Spatial DB Interoperability
Based on CORBA or J2EE
The second level is the implementation specification
for spatial data interoperability based on Web Services.
It follows the specification of spatial data sharing
models and interoperation based on XML. When these
are implemented among different GIS software
packages, the internal spatial data is transformed into
the data flow of the common interface description
specification (the format is ASCII). The other system
will read the data flow to itself system.
There are two forms of implementing interoperability
specification based on XML. One is to transform one
data set entirely into the data format described by XML.
Other systems can access the data set according to the
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