4 The application architecture and its realization

We realized a prototype of the system on an Open Source platform: as a web server we used Tomcat [10] and chose the Jakarta Struts framework [11] for the system implementation. The latter choice was motivated by the fact that the Jakarta Struts framework combines the advantages of the MVC pattern with the ones of a well-tested servlet controller with useful tag libraries.

In the Struts framework (Figure 2) the role of the controller is played by the object ActionServlet (configuration file struts-config): the ActionServlet manages all the requests and redirects them to the associated applications. The Action classes and the ActionForm type classes are used to encapsulate the messages and process the requests: from the point of view of the MVC pattern they represent the model. Finally the view part (content presentation) is obtained through XHTML (JSP) pages.

Figure 2: From [9]: the MVC pattern implemented with Struts.

The stereo reconstruction procedure has been subdivided into six steps (Figure 1), according to the following key points:

• User interaction with the system: in some steps an appropriate interaction of the user with the system is required; to achieve it the feedback of the system toward the user itself was carefully developed;
• Presence of critical operations: some steps are more important than others, for a satisfactory result in the reconstruction process - one of them is the feature matching step;
• Extended debugging: since the problem is mathematically difficult, sometimes unexpected results are quite hard to explain; the debugging of the latter situations is simplified by the modular approach to the problem that we have followed.

Every step in the reconstruction process is implemented using an Action object, and a JSP page to issue the output or error messages. In this way future extensions of the functionalities of the model are achieved by adding an Action and the associated JSP page. Moreover, since the presentation environment is separated from the application logic, it is easy to tailor the interaction with different classes of users through suitable interfaces.