ISPRS, Vol.34, Part 2W2, "Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
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including geospatial data visualization and map annotation and 
symbolization. The other is related with research domain. Models 
are changed with domains such as environment administration 
and land use and so on. 
In our system, all sites have identical structures in the sense that 
each has a query server, and an ORB with several services 
objects that provide common services including naming services, 
persistence services, query services and so on. Since users may 
request data stored at remote sites, the query are distributed to 
multiple sites to execute. The query service is also responsible 
for initiating execution of the query. The ORB provides 
mechanisms for inter- and intra-site communications between 
objects. The naming service is used to locate named objects. 
The persistence service objects provide an object-oriented 
interface for the data persistently stored in the local service. 
3.5 Integration of GML(Geographic Makeup Language) and 
CORBA 
The emerging set of XML Standards is gaining widespread 
industry support in content management, delivery, and 
presentation at the web-based front end of today’s Enterprise 
Systems. As spatial data will be encoded in an GML form and 
sent across the internet, a need for native processing of GML 
data under CORBA is required. Integrating CORBA and GML 
efficiently processed by CORBA systems providing data access 
and query services to the web; GML data to be sent back to web 
systems; CORBA Objects be accessed through XML based 
Messaging protocols. The Integration of CORBA and GML is a 
small piece of the overall solution to the provision of Enterprise 
Level software systems for today’s emerging web-based GIS 
and traditional GIS migrating services to the internet. 
Fig 3: GML and CORBA integration figure 
The diagram (Fig 3) illustrates the GML processing system 
implemented using a Java ORB client embedded in the Web 
Browser, with a Java ORB server processing the received 
document, storing relevant details in the order database, and 
generating an GML encoded receipt which it returns to the ORB 
client. Both the sent and received documents are serialized into 
text before they are sent or received, and require parsing into a 
manipulative form in order to be processed in GIS client. 
4. LOAD BALANCE AND SECURITY 
Object migration is the process of terminating an object 
implementation on one host, and then starting it on another host. 
Object migration can be used to provide load balancing by 
moving objects from overloaded hosts to hosts that have more 
resources or processing power (there is no load balancing 
between servers registered with different ORB servers). Object 
migration can also be used to keep objects available when a 
host has to be shutdown for hardware or software maintenance. 
The migration of objects that do not maintain state is transparent 
to the client program. If a client is connected to an object 
implementation that has migrated, the ORB service will detect 
the loss of the connection and transparently reconnect the client 
to the new object on the new host. 
When a distributed GIS based on CORBA is deployed over the 
Internet or Intranet, many security restrictions can apply to the 
system, including the following: 
• Java sandbox security prevents unsigned Java applets 
from communicating with servers other than the ones 
running on the host machine from which the applets 
were downloaded. 
• Server-side firewalls can prevent the client from 
accessing certain hosts. 
• Client-side firewalls can prevent incoming connections 
or prohibit protocols other than HTTP. 
When certain restrictions prevent the clients from connecting 
directly to the server, the client can choose to connect to the 
gateway if the server object reference has the necessary 
information. The clients can send messages to gateway; The 
gateway will forward the messages to the server. 
When certain restrictions prevent the server from connecting 
back to the client to do callbacks, the server can choose to 
connect to the gateway if the callback object reference has the 
necessary information. The server can send callback messages 
to the gateway; The gateway will forward the messages to the 
client. 
5.SYSTEM ANALYSIS AND DESIGN OF DISTRIBUTED GIS 
Because of the Object-oriented characteristic of CORBA object, 
the main system analysis method is object-oriented. At first, 
skeleton structure of the system is necessary. Then IDL Interface 
file should be generated. After deep analysis of user demand, 
the main relationship of objects and operations can be 
abstracted. IDL (Interface Definition Language) is adapted for 
describing the relationship. Because CORBA realize the 
communication function, developers can just focus on 
developing your application. The main develop steps are as 
follows: 
• analysis the system demands; The main demands 
include the main system function and the kind of the 
clients, the distribution of spatial data, the update rate 
of database and the amount of maximum clients 
• building up the abstract model of the system; In this 
part, the relationship between system functions and 
decide how the functions are divided into the different 
ORBs. 
• building up the object model; According to the 
Object-Oriented design method, objects can be 
described with UML(Uniform Model Language).