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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