but the code is compiled to an intermediate code interpreted by 
a virtual machine. Using a virtual machine, Java code is fully 
hardware independent. What makes Java so important, is the 
built-in support for network access via HTTP. Java programs 
can fetch code and data over the network at execution time. A 
Java program can not only execute code on the local computer 
but also on the computer it was loaded from, by using Java 
remote objects. To guarantee security a number of configurable 
security options was integrated into Java. Since Java is 
interpreted at runtime, it’s execution is slower than C programs, 
for example. But for most applications the performance is still 
sufficient. 
Full support for graphical user interfaces, image processing and 
graphic routines exists to implement state of the art search and 
retrieval software for image archives. With Java for the first 
time ever, it becomes possible to implement platform 
independent retrieval systems with all the functionality only 
stand alone software offered so far. Netscape, Microsoft, SGI 
and other hard and software companies have licensed Java to 
integrate it into their network products. A recent Java extension 
to interface popular relational database systems like Sybase, 
Oracle or Informix with native Java calls, makes Java a very 
useful tool to implement any WWW-based database retrieval 
client. 
4.2 Applets 
Netscape is the first company to integrate a Java interpreter into 
the latest version of it’s WWW browser, the Netscape 
Navigator 2.0. Netscape also extended the HTML language to 
make it possible to include Java programs into an HTML 
document in the same way images are included. These included 
Java applications are called applets. 
This combination of Java and the Netscape Navigator helps to 
integrate search and retrieval software into HTML documents. 
Once this document is loaded by the browser, the applet is 
downloaded and executed on the local computer. Using the 
caching facilities of Netscape, the applet will be stored on the 
local filesystem. Reloading the program is not necessary until 
the code has changed at the server site. In the case of repeated 
access this will reduce the required network traffic to a 
minimum. 
Data providers still can offer their special purpose products 
without the problem of porting software to different platforms 
or expensive distribution of software upgrades. The user has to 
maintain only a single software product, the Netscape 
Navigator so far, and benefits from the functionality of software 
written in a high level programming language. As long as there 
are no compulsory style guides like those for Motif 
applications, there will still be a broad variety of different looks 
and feels. 
4.3 Javascript 
Netscape also integrated a new script language called Javascript 
into the latest version of it’s navigator. Javascript is comparable 
to the macro language of other applications and has nothing to 
do with Java besides it’s C- like syntax. There is also no 
compiler for Javascripts. The code is embedded into the HTML 
document and executed when it is loaded. 
5 AN EXPERIMENTAL SYSTEM 
5.1 Motivation 
Parts of the dataset generated from the Magellan spacecraft’s 
mission to Venus are available at the European Magellan Data 
Node (EMDN) at the University of Technology in Graz, 
Austria. A goal of this project is to provide access to these data 
to the European scientific community. To reach this goal an 
image retrieval system has been implemented stepwise by 
different student projects. This also serves as a testbed for the 
development of a Java-based information system. It is still an 
evolving project where modules are replaced or improved 
  
    
   
    
   
Web browser 
with Java support 
  
   
    
     
  
(optional) 
Venus Map 
Database 
data & applets 
x j020101d al IH = jouraju] / 
  
  
   
    
   
  
   
  
   
Java driven 
Web Server 
Data 
Archive 
   
     
Venus Map 
Database 
  
  
  
Management 
  
Hardware independent 
components 
Arm | Contol flow 
——» Data Flow 
Fig 3: Layout of the experimental system. 
    
    
    
Unit 
(image processing) 
© 1996 Wolfgang Walcher 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996 
freq 
use: 
acc 
inst 
Wh 
suci 
imp 
abo 
tota 
oth 
crat 
Ver 
be i 
par 
the 
dor 
The 
spa 
sek 
con 
Vis 
dat 
are 
pro 
5.2 
Th 
dat 
nar 
the 
spa 
strı 
de