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

By "tier" do you mean a "layer" in your software stack? The word "tier" is better used to describe the physical components of your system. If you are using ASP.NET, you probably already have a "3 tiered" system -

1. Browser displaying web pages
2. IIS Server hosting your app
3. Database Server with your database

But you are possibly putting all of your code into a single software "layer" - specifically, the code behind file of your aspx pages. You want to move from a single layer to a 3 layer approach. The classic "3 layer" software architecture consists of the following -

1. Presentation Layer

2. Business Logic Layer (BLL)

3. Data Access Layer (DAL)

_{(source: asp.net)}

For a typical ASP.NET app, you might apply this as follows. First, you create a LINQ2SQL file (.dbml) containing the objects for your database access. This is your Data Access Layer (DAL).

Next you might create a DLL to contain your Business Logic Layer (BLL). This layer will access the database via the DAL, manipulate it as required, and then expose it via a simple interface. For example, if your application displays a client list, your BLL might have a public function called GetClientList() which returned a list of clients.

Finally you would set up your code behind files to instantiate the BLL and wire it up to the interface components. This is your Presentation Layer. For example, it might take the data returned from your GetClientList() function and bind it to a data grid on the web form. The idea is to have the presentation layer as thin as possible.

This seems a little long-winded to describe, but it's pretty straight-forward once you have done it a couple of times. You will find that separating out your application like this will make it much easier to maintain, as the separation of concerns leads to cleaner code. You will also find it much easier to upgrade or even replace your presentation layer, as it contains very little smarts. Finally, you will get to a point where you have a number of very useful BLL libraries that you can easily consume in new applications, greatly improving productivity.