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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004
processes are done in one center and which has a graphical data
base, is called “Thin Client” architecture. In this architecture,
visual objects required by a client are sent in known raster
formats such as jpg, gif, etc. The most of the geographic
analysis is handled by the server, while the client only displays
the HTML pages and runs Java Scripts.
The system, which consists of the complex GIS software and
GIS data base, locates on the server. The data required by a
client is prepared in the server, and then compiled and sent to
the client's browser in HTML format (Figure 1). The biggest
disadvantage of a server based solution is that a user can not
entirely accomplish the functions expected from GIS.
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GIS Software
Spatial Database Poe )
HTML
Server Client
Figure 1. Thin Client Architecture
2.2. Fat Client
In order to overcome the disadvantages of the “Thin Client”,
“Fat Client” architecture was developed. In this architecture, the
task of the server is limited to only sending the data, while most
of the geographic analysis is handled by a client in a platform.
The client's web browser is improved by adding new plug-ins
such as Java language, java applets, and ActiveX (Figure 2).
Some of the client based solutions may require a user to install
entirely different program in stead of a browser improved by
the plug-ins. In this architecture, the server sends a client the
data in vector format, which is more complex than raster format
data (Eraslan, 2003).
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Figure 2. Fat Client Architecture
In internet based GIS, Java is mostly preferred computer
programming language. In fat client architecture, Java is
generally used in the software, which is distributed to the end
users because it is simple, object oriented, independent of the
platform, dynamic and high performance language.
The most important advantages of a client based solution are
that user interface can be improved and the solutions are
reached using data in vector format. Client based solutions
using vector data allow many geographic analysis and graphical
tasks to be performed locally. It increases the performance by
providing the image alterations without data transfer on the
Screen. The fundamental tasks of GIS such as buffering,
overlaying, route analysis can be performed very effectively by
using vector data.
44]
There are several disadvantages of client based solutions. The
reliability of the data decreases due to transferring the data to
the user. Some problems may occur due to plug-ins such as
Java, ActiveX, and incompatibility between software and
computer system. None of the software including Java, which is
developed to perform in any system, can be compatible with
every computer systems. Therefore, some of the potential users
cannot login to the web page or can simply give up. They may
also have some problems installing software and this can
prevent users to benefit from the web page if technical support
is not provided. Besides, the time spent on installing software
may cause a problem since some of the potential users don't
like to wait for installing software while there are other web
pages where the data can be reached instantly as just logging in
to the site (Eraslan, 2003).
In both thin and fat client architectures, there are various
technologies, languages, and plug-ins, which provide
interaction between by server and client. The technologies such
as Cgi, Asp, Php are run by the server and they use script
languages. “Scripts” are small programs that run over the
server. They are used to reach data bases and files in the server.
“Scripts” are written by computer programs such as Bourne
Shell, C Shell, C/C++, Perl, Python, Tcl, Visual Basic,
JavaScript and VBScript. The features of a browser can be used
more effectively and efficiently by client based scripts. For
example, response of a HTML page to a user when he locates
and clicks on a mouse is done by one of these scripts.
Java, VRML and XML, on the other hand, are the languages
that are run by the client. The client also uses plug-ins such as
ActiveX and Java Applets. ActiveX controls, also known as
OCX, can run over the web just like Java Applets, except
ActiveX components only work on Microsoft Windows
environment.
3. E-GOVERNMENT APPLICATIONS
E-government concept has the ability to transform relations
between citizens, businesses, and other branch of the
government. In general, there are two most important
applications; interactive web maps that can be queried on
Internet and spatial data based e-government information that
can be accessed by the clients or public on the Internet.
3.1. Application 1
Web based Campus Information System of Gebze Institute of
Technology (GIT) presented in this section is a good example
for the first type of spatial based e-government applications. In
this Information System, campus maps can be queried
interactively and many graphical and written information can be
obtained about GIT and its departments. “GIT University
Geographic Information System ()" has been also developed
on ArcView 3.3 platform as a part of the Campus Information
System (CIS). The main framework of web module's
interactive pages is generated by using a plug-in called HTML
ImageMapper", which is a macro runs on ArcView platform.
By using various possibilities of ASP technologies and HTML
language, the system capabilities have been increased. Besides,
by using animations (visual effects), it is aimed to give users the
feeling that they are actually in the campus.
The GIT University Geographic Information System is
supported by Gebze Institute of Technology.
