3 Tier Architecture - In need of an example

Question

Presently I am working using single tier architecture. Now I am wanting to learn how to write code using 3 tier architecture. Please can you provide me with a simple example

Answer 1

Presentation layer: put everything that is related to user interface. (What the user sees)

Business layer: everything that is related to the logic of the application (How is the information coming from presentation layer treated)

Data layer: provide an abstraction of the underlying data source(s) (Where and how the information coming from/going to business layer is stored)

Each layer should know as less as possible about the other and it should be a top down approach:

• the data layer should know nothing about business and presentation
• business layer should know about data but not about presentation
• presentation should know about business but not about data

Simple example:

Website:

• Presentation: all the graphical things, fields where user inserts data, menus, pictures, etc.
• Business: all constraints about the data (unique name, name without symbols, valid date, etc), methods for manipulating business objects (create new user, add new order, etc)
• Data: Methods that access the underlying database.