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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
With the development of modern information
technology, a great deal of geo-spatial data from
different sources is produced almost continuously.
With the development of computer networks and the
growing popularity of the Internet, more and more
information must be processed in different software
packages to be distributed overthe network. Thus, the
issue of how to acquire data rapidly from different
sources, integrate the data for analysis, and realize
heterogeneous spatial data interoperability in a
distributed environment becomes very important.
As information sharing is an important requirement for
the development of modern information society, GIS
interoperability is an essential technology for
information sharing. The geographic information
sharing and interoperability has been an important
direction in GIS.
A lot of research in geographic information sharing and
interoperability has been carried out for decades. A
series of methods for geographic information sharing
and interoperability have been proposed. A number of
standards have been constituted as well. This paper
briefly introduces the methods for geo-spatial
information sharing and interoperability. Then, the
standards constituted by OpenGIS and ISO/TC211 are
introduced in detail. The techniques to implement
geo-spatial data sharing based on Web Service
technology are introduced in the context of the
accomplished researches and experiments.
2. BASIC METHODS FOR GEO-SPATIAL DATA
SHARING
At present, there are three methods to realize
geo-spatial data sharing, namely, through data
exchange mode, database direct access mode or
database interoperability mode.
2.1 Spatial data exchange mode
Each GIS software package has its own internal data
format and data storage method. In the past, many GIS
software manufacturers did not directly provide the
functions to read/write internal data to their users. For
data exchange with other GIS software, an external
data exchange format was thus needed, such as DXF
for AutoCAD, MIF for MapInfo and E00 for Arc/Info.
Generally, the underlying data format is ASCII. Users
can read/write such external data with use of the users’
guide. However, the external data exchange formats
were defined by each software manufacturer,
respectively. Thus, the content and semantics would
typically differ. Many countries and industries have
constituted their own data exchange standards,
requesting that other countries or other organizations
use a mutual data exchange format, such as DLG and
119
STDS in the USA, ASDTS in Australia, NTF in the UK,
DIGEST with NATO, CNSTDF in China, and so on.
Besides, some companies have developed specific
geo-spatial data exchange software.
The spatial data exchange standard or the spatial data
exchange software has solved the problem of spatial
data exchange between different GIS software.
However, it is not an optimal method. This data sharing
is based on files, which can be only used for data
integration but cannot realize real-time data sharing at
the feature level. Thus, the interoperation between two
systems is not real interoperability. In one aspect,
because of the lack of a unified description method for
spatial objects, different data formats use different data
models to describe the spatial objects. Thus, after data
exchange, information of the original data cannot be
expressed accurately, and information loss occurs.
Moreover, real-time updating of spatial data and data
consistency cannot be realized via external data
exchange. For example, the planning bureau of a city
may have several departments. Different departments
purchase different software based on their own
requirements. For example, the department of
surveying and mapping may use GeoStar, while the
department of pipeline network management may use
Arc/Info, and still other departments may use MapInfo.
The software packages may exchange data via external
data exchange files. The problem is that the three
databases are updating constantly and the update only
is only reflected in its own database. If the
administrator for urban planning does not exchange the
spatial data from the surveying database or pipeline
network database every day or every hour, the data he
uses might be the data as current a few days or even
months ago. Then, the spatial data for planning will not
be current and accurate. As a result, it is necessary to
study and constitute the methods and standards for
spatial database online sharing.
2.2 Interoperability Based on Direct Access
Database direct access means that a GIS software
package can directly access multiple databases using
different data formats. Direct access not only avoids
the fussy course of data exchange, but also allows users
to obtain online data by accessing another database
directly. Direct access provides a data-sharing mode for
multi data sources with more economic and practical
value.
Direct access assumes sufficient understanding of the
data format and data model in the spatial database at
hand. If its internal data format is not public, direct
access to it is difficult. If the data format of the host
software changes, any software package for data
integration must re-address the changed format and
then update its own. However, it is seldom publicly