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The 3rd ISPRS Workshop on Dynamic and Multi-Dimensional GIS & the 10th Annual Conference of CPGIS on Geoinformatics
Chen, Jun

ISPRS, Vol.34, Part 2W2, "Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
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
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.
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
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
• 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
• building up the object model; According to the
Object-Oriented design method, objects can be
described with UML(Uniform Model Language).