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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
defined specification and import it into the internal
system. This method is similar to a data set
transformation with a spatial data transformation
standard. The other method is a real-time read/write
transformation. When one system requests data from
another system, it sends a massage to boot and start up
the read/write and query method with the XML or
SOAP protocol, to access spatial objects in the spatial
database management system at real time, and then
transforms the data into the data flow of the public
format defined by XML. The system may acquire the
object data at real-time, which results in the real-time
online data sharing and interoperability. The data flow
of interoperability specification based on XML has an
ASCII format, which is easy to understand and to
realize multi-hardware-software-platform
interoperability. It can be used in many ways as spatial
information distribution service and spatial information
mobile service... At: present, . the . spatial... data
interoperability based on XML is a hot research
direction, which involves many concepts and mainly
includes the related techniques of web services. OGC
and ISO/TC211 have constituted spatial data
interoperability specifications based on XML as Web
Map Service Specification, Web Feature Service
Specification, Web Coverage Service Specification and
GML, a geographic information markup language used
for spatial data exchange and online transformation.
Figure 4 shows the spatial data interoperability
implementation specification based on XML.
Spatial = datal
query,
processing &
transformation WMS
component WFS Data Spatial
x Transfor |Data
(GML —>[mation [Browser
Spatial data )WCS
query,
processing & »
transformation
component
Figure 4 Spatial Data Interoperability Implementation Method
Based on Web Service Technology (XML)
In the above two forms of spatial data interoperability,
the efficiency of interoperability using an API is higher.
The adaptability of interoperability based on XML is
wider but has a lower efficiency. The interoperability
system based on API is often used in the LAN of an
organization, while the system based on XML is
generally used on the Internet.
3. GEOGRAPHIC INFORMATION SHARING
STANDARDS
3.1 Open Geographic Information Specifications
The Open GIS Consortium (OGC) is an industry
organization with international members. It now has
more than 220 members including software companies,
governmental agencies, colleges and universities. Its
major task is to develop Open GIS Specifications and
enable them to transparently share heterogeneous
geographic data and process resources in the network.
At present, the geographic data interoperability
specification constituted by OGC is classified into
abstract specification and implementation
specification.
3.1.1 Abstract Specification
1. Objectives
The objective to compose an abstract specification is to
build a concept model and prove that the model can be
used to establish the implementation specification. The
abstract specification includes two models derived
from Syntropy object analysis and design.
The first model is a basic model. It is simple and is
used to establish the conceptual links between the
software or system design with the real world. The
basic model is to describe how the real world works or
how the real world should work.
The second model is an abstract model. It is the essence
of abstract specification, which is used to define the
final software system of the implementation
middleware. The abstract model is to describe how the
software should work. The objectives to develop this
abstract specification include:
e Relate the software and system design with the real
world;
* Acquire and accurately state demands and field
knowledge, so that the risk bearer can understand and
make decisions;
e Consider the system design;
* Acquire the design decisions in indefinite forms. The
forms and the demands are separate;
* Produce uscable working products (such as
certification of prototype and concept
implementation);
* Organize, discover, screen, index, check and edit the
information of the related large systems;
e. Seek for various economical solutions;
e The abstract specification, especially the abstract
model can be applied for all the mentioned objectives.
In addition, it provides sets of “languages” for
interoperability.
2. Topics
The central topic of OGC is to share information and
provide service. Thus, it has two central technical
topics, i.e., to share geo-spatial information and
