3 Migrating on the net: the design of WEB3R

The procedure described in the previous section has been embedded into a client-server architecture, to create a novel web-based service. A client can be whatever system equipped with a browser and an Internet access.

More in detail, the aim is creating a dynamic, modular web application with the following functionalities:

• Constructive interaction with different kinds of users;
• Easier and effective management, upgrade and extension of the system.

The full reconstruction system may also include a subsystem devoted to the image acquisition process. The server side frame is made by the following components:

1. Web Server: it deals with the communication with the clients, sending the HTML pages and receiving the requests; it is also a container for Java servlets;
2. Frame grabber: hardware component used to acquire images from an analogical camera; in case of digital cameras the frame grabber can be substituted with an appropriate software interface;
3. Reconstruction modules: software that implements the reconstruction process as summarized in section 2;
4. Service management modules: software managing input and output operations, code execution, error management, ....

We have always kept as a guideline the substantial decoupling between the content presentation environment and the computational/elaboration framework. For this reason the design has followed the MVC (Model View Controller) paradigm [8].

The MVC logic is relevant to all applications that contain a graphic interface, through which information is conveyed to the user in different screenshots. This is especially true when the information has to be continuously updated.

As a matter of fact, in the MVC paradigm the input by the user, the modelling of the external world and the visual feedback are explicitly separated and managed by three distinct objects called Model (business functionality), View (presentation logic) and Controller (control logic).

Each of them is specialized in a task and to each of them a different level of logic is associated. The functions of each level can be summarized as follows:

• Presentation logic: part of the application that deals with the presentation layer, containing the user interface and the web technologies (for instance XML, XHTML). It is responsible for the visualization of information, or how the application visualizes the information, but not of how this information is obtained.
• Control logic: it deals with the application flow and connects the interface and the application; it receives and interprets the HTTP requests in order to choose the next step in the application according to the user input.
• Application logic: also called business logic, is the core of the application, being responsible of all the tasks dealt with by the application. It contains the principles, algorithms and functions of the service.