Three-tier Architecture

In a three-tier architecture [3], the logical architecture of the entire system is split into three levels (see also Figure ):

Presentation Tier

The presentation tier is the interface to the user. This layer may do some input verification when rich clients are used.

Application Tier/Business Logic Tier

The application tier is the layer where the principles and rules of the business have to be applied.

Data Tier

The data tier is an abstraction layer to integrate a database into the application.

Figure: Three-Tier Architecture (Source: [10])

The three-tier can be seen as an extension of the client-server approach and is the most frequently used special case of a multi-tier architecture (see Section  on page ). The different layers may be on different machines. The basic idea behind the three-tier architecture is to integrate already existing data and to facilitate changes of a technology used in a layer. As an example it is sufficient the adapt the data tier when the database used changes. The remaining components of the application will remain unaffected.

Applied to this project, the following structure of the application would be as follows.

• The presentation tier corresponds to the web interface that the user uses in his favourite navigator (e.g. Firefox). It is used to display or modify tasks.
• The application tier is used to transform the information received from the web interface and to guarantee compliance with the business logic.
• The data tier simply executes the queries defined by the application tier.