T.A.C. is a web application built up using JAVA, by that means firm and reliable.

Concerning hardware we suggest for best performance a Linux server and Mysql database.
Application is developed in Linux environment, Web container Apache Tomcat, pure Java technology and with Mysql me database. Since it’s a three levels architecture, it’s easily adaptable to hardware demand of users.

Architecture

The essential components of a web application, from a certain point of view, is similar to a traditional client/server application.
A client/server application is made by a client that implements the user interface using some communication and process functionalities, second is made by a server which provides a list of services such as management and data access of a given database.
In the Web sphere, the relationship between client and server is a little more well-constructed in order to allow integration among different components. A web application is based on standard software elements independent from main features of the application itself and from software and hardware platform where this runs.
A web application, in most of cases, is developed on three levels or more logical-functional levels:

1) Introduction level - It represents user interface of application and look after of data acquisition and results visualizations;
2) Intermediate level - it look after of data processing depending on so called business logic, specifically the category of rules that statue data are relevant and their relationship consistent. The elaboration process of intermediate level generates the outcomes required by the user;
3) Data level - It represents the category of services offered from applications web-indipendent, such as database manager, an email manager system, etc etc.

Not always, the logical levels of a web application matches to physical locations in the network . We begin from the case in which each of the three levels is placed on the same machine to the one in which we have several different distributions, but we may argue of a case where each level has a match in its specific machine.
Later we’ll analyze the architectural levels.

Introduction level
It represents user interface of web application and makes the same function of client in the standard applications client/server.
It is made from the different combined components: browser, HTLM documents, applet Java, ActiveX controls. The utilization capacity of this components from the client platform is one of the main problems, building up this level.
Solutions can be different: we can exploit at best the processing capacities of the client but we can also build up a universal introduction level.
Usually, the identification of application execution context gives a strong contribution to define the solutions to adopt in the way to building up the process.
A further element to keep in mind is the complexity of application user interface. The HTLM language born for distribution of documents within distributed environments, doesn’t allow to develop very advanced users interfaces (drag-and-drop, tree-view control, tabbed control, etc.). One solution is to foresee a given quantity of HTLM standard pages enriched by Java applet.

Intermediate level
The Intermediate level of a web application contains its own processing logical scheme.
This is able to guarantee data request and processing requests of the client. The way of building up the intermediate level often depends from the features and from the supported technologies of web server, sometime from installed components on application server as well. In every case the main functionality of the web server supporting the whole application is processing processes backing.
Related to the typology of application to develop, it’s good to foresee particular functionalities, such as:

• management of transactions: reliable management of data flow;
• management of security and confidentiality: management of security on access to the application and confidentiality in the information transmissions. management of security is often achieved through the authentication of user password, meanwhile confidentiality is guaranteed by peculiar protocols such as SSL (Secure Socket Layer) or PCT (Private Communications Technology).

The Intermediate level of a web application can be made of a given quantity of script, components and programs among themselves and with the server interacting trough the following technologies:

• Common Gateway Interface (GCI): it allows activation of a program or a script on client demand (portable on every platform).
• Internet Server Application Programming Interface (ISAPI): it allows the execution of a dynamic library (DLL) within a memory space of the web server (but it works only on windows environment).
• Java Server Pages (JSP): it allows translation of script in the web server environment and dynamic creation of web documents (it works only on windows environment and web server).
• Java Servlet : it allows to execute Java classes on client demand (portable on every platform)

Data level
Data level provides services not directly available through web server. These services are usually provided from independent applications from web environment and often are the former applications installed in a company system.
Typical examples of application working at this level are:

• data server
• mail server
• electronic documentation server.

It’s used to foresee components of application architecture that work as connectors between intermediate level and data level. In fact, using connectors for interaction with external non-standard application, you make easier the work of maintenance in case these could be modified or replaced (f.i. ODBC,OLEDB).