Saturday, October 27, 2007

3-TierIntroduction

Introduction:
Application Architecture is the most important process of developing a good application. Some people tends to jump into coding without any architecture laid. Later we see those people changing the architecture and finally the
application had to be developed from the scratch with the correct architecture.
In this article I will describe some details about how you can improve the architecture of you application. This article is targeted to the beginner's audience.
Three layered approach:
Three layered approach is the most common approach taken to build a
web application. In this approach application is divided into three layers.
1) Database layer:
The
database layer contains the tables, views and stored procedures which deals with the database. Usually this layer is created before making the other layers. Database layer is also the most important layer in the application architecture that's why most of the time is spent making the database layer solid so, the pillars of the application are strong and scalable.
2) Business logic layer:
Business logic layer contains the logic of the application. Like the database layer this layer is not exposed to the users directly but a user interface is provided to do so.
3)
Presentation layer:
The presentation layer is what the user actually sees. The html pages with some animation, the textboxes to take input and message boxes to alarm the user of the operation of his action. Presentation layer must be developed in such a way that it can be changed without doing any changes to the business or the database layer. This means that the presentation layer must be independent of the database and the business layers. Also the presentation layer should be made in such a way that changing the presentation to the user will take less time and effort.
Tips about the database layer:
1) Database layer as I pointed out earlier consists of a database, stored procedures and tables etc. Its always good to use stored procedures instead of Ad-Hoc queries. Ad-Hoc queries have the danger of SQL injections. Stored procedures on the other hand are more fast to execute and gives the performance boost. Since those procedures used often are executed from the cache.
2) It's very important that you normalize the database design. You should carefully map out the one-one, one-many, many-many
relationships. If normalization of the database is not handled carefully at the right time it can destroy the whole application and you may have to start from scratch.
Tips about the Business layer:
Business layer is where all the cool stuff happens. Usually for each subject (noun) in our specification we make a class for it. Suppose we are making an application where users and
sends emails and receive messages depending on if their email is sent or not.
Some users tends to keep all the business logic in the presentation layer. This approach is very dangerous since user has a direct interaction with the business logic and it becomes easily hackable. That's why business logic is always kept in the class libraries this approach makes the separation of the user interaction with business logic and also makes the libraries portable so, it can be used by some other same type of application.
Sometimes its also a good idea to map the class fields to the database column names. Suppose our application stored articles so, our mapping class will look something like this:
public class ArticleDetails{
public string Title;public string Url;public string Description;
}
The advantage of using this approach is that if you make changes in the Title, Url, Description than you will only need to send the object of the ArticleDetails class. This is also a good approach since if later you decide to add one field to your database due to bad design you can just add the same field to this class without having to play around with the business logic methods.
Data Access Application Block:
I also explicitly use
Microsoft.NET Data Access Application Block. Application Blocks makes the code simpler to understand and modify. Another good reason to use the application block is that it makes the code more readable if many coders are using the same block instead you find yourself reading every line of code written by the developer and trying to understand his coding style of accessing the database.
Messages Class:
Just like the
Data Access Application Block every frequently used operation should be converted into a class for easier access. This includes Cache Block, Exception Handling Block etc. I will talk about the Messages class whose purpose is to alarm the user with a message about the operation that he has performed.
Sometimes you want to print a message "Data has been successfully entered" if the transaction was successful and "
Data not entered" when, the transaction was a failure.
Most of the developers perform this task by simply adding the if-else block in the presentation layer.
bool isDataInserted = code.AddCodeSample(txtTitle,txtDescription);
if(isDataInserted){
// Data inserted successfully
}else{
// Data not inserted
}
This is a common approach used by developers to alarm the user of his operation. The problem with this approach is we are repeating code, meaning that each of the event that is inserted, deleted, updated, selecting, editing will have the same kind operation with a different message and we will be writing same 4-5 lines everywhere. Hence, its a good idea to make a class whose main purpose is to return messages. You can call this class DBMessages.
// message returned after the insert operation
public static string InsertMessages(bool isAdded){
if(isAdded){
return "Inserted";
}else{
return "Not Inserted";
}
}
// message returned after the Update Operation
public static string UpdateMessages(bool isUpdated){
if(isUpdated){
return "Updated";
}else{
return "Not Updated";
}
}

As you see now you only have to write a single line of code to get the message. Here lblMessage is a label control.
lblMessage.Text = DBMessages.InsertMessages(isAdded);
Using this approach you can also modify your message in one place and it will be changed everywhere.
Tips for the Presentation Layer:
Presentation layer design should always be consistent since this layer will be the one that will change often. Consistent design can come in the form of the Cascading Style Sheets and User Controls. By using Cascading Style Sheets your page has a consistent look and feel. A simple change in the Cascading Style Sheet will bring changes to all the pages without even touching them.
User controls is another way for making sections that are easily changed. If on the other hand if they are not marked as a user controls we will have to go to each page and manually change it which, is a pain.
Conclusion:
If the architecture of the application is made correct. The rest of the coding (Implementation Phase) becomes really easy.

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