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4. SYSTEM ARCHITECTURE 
41 Description of the physical system 
The system is based on a server client architecture and in 
particular a n-tier logic architecture based on n-tier logic 
component ((Peng and Tsou, 2003). It consists of (fig. 1): 
- a Web server (WS); 
- a Map server (MS); 
- a Print server (PS); 
- a Database server (DS). 
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Figure 1 - Physical architecture 
The above described structure is only the basic configuration 
and in order to guarantee for high availability more server 
should be integrated into the system to assure redundancy of 
services and data. Availability, as well as performances of the 
System, have not been considered of primary importance for 
this project and it has been considered that this aspect should be 
better managed by the IT Department. 
It should be clear that this architecture represent the physical 
structure of the node managed by the RERGO. Obviously, the 
other nodes of the interoperable network may use a different 
architectures. 
42 Software architecture 
The software architecture show the distribution of different 
modules on the physical components. 
Considering the presentation tier a large series of client 
application are available to be used: 
- the Web browsers used to access the WS for both Web 
pages and web mapping; 
- OGC WMS and WFS compliant clients: 
- Database client applications. 
The software managing the logic tier consists of a Web Server 
and Java Container (Apache + Tomcat), a Web mapping 
software (ESRI ArcIMS) and of a PDF maker application. 
The Web Mapping application and it has been configured as a 
three-tier architecture and integrated with an OGC WMS and 
WFS compliant top layer. 
nsing and Spatial Information Sciences, Vol XXXV, Part B4 . Istanbul 2004 
Stuidard Configuration 
  
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Figure 2 -ArcIMS three-tier configuration (courtesy of ESRI) 
The data tier is managed by a client-server database and a GIS 
gateway, in particular Oracle 8i and ESRI ArcSDE. 
This software architecture, even requiring a quite complex 
administration and management presents a series of advantages. 
The users having different needs can access the system at 
various level using a large set of client applications. Internal 
user can access the database through the GIS gateway, other 
nodes of the network can access the system through the OGC 
interfaces, everybody can visualize the maps by the means of a 
standard browser. 
Moreover the spatial database system, in the meaning of DBMS 
plus Middleware (Shekhar and Chawla, 2002) allows to manage 
versioning and user privileges. 
In this way data are maintained in a single database and made 
accessible from all the users and application who have the 
permission. 
5. DESCRITPION OF THE WEB MAPPING 
APPLICATION AND OF THE METADATA EXPLORER 
5.1 Metadata 
Metadata have been made available to the users through a 
Metadata Explorer Web application. 
Users can search metadata either for keywords or attributes or 
for geographical extent. 
The metadata have been also organised in a hierarchical 
structure that can be easily browsed. 
The system integrates a gazetteer and a search map to facilitate 
users in finding metadata of data regarding to their area of 
interest. 
The metadata XML files are presented through the Web by a 
simple interface but, since the system made use of XSL to 
render the XML file content, it is quit easy to use the proper 
style for each kind of metadata or application. 
In the case of Web map services available online it is possible 
to visualise the data in a standard Web mapping interface 
integrated into the metadata explorer environment and 
providing simple browsing tools. 
The metadata explorer integrates an authentication system that 
allow the metadata manager to decide what metadata any single 
user can access. 
5.2. OGC WMS and WFS compliance 
The system provides for two OGC compliant interface 
accessible using any WMS and WFS compliant client 
application. The OGC WMS interface running on the top of the 
Map server allows users to access the data and maps as images 
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