1. Objectives In this session, you will learn to:
Identify the types of application architectures
Identify the need for an n-tier architecture model
Identify the features of the n-tier architecture model
Identify the advantages of using n-tier architecture
Identify the steps to develop an n-tier model

2. Application Architectures
Applications are developed to support organizations in their business operations. The functions performed by an application can be divided into three categories: user services, business services, and data services.
Application architectures are of the following types:
Single-tier
Two-tier
Three-tier
N-tier

3. Single-tier Architecture
The Single-tier Architecture
In the case of a single-tier architecture, a single executable file handles all functions related to the user, business, and data service layers. Such an application is also called a monolithic application.
The following figure depicts the components of the single-tier architecture:
Single-tier Architecture
User Services
Business Services
Data Services

4. The Single-tier Architecture (Contd.)
Examples of single-tier architecture can be found in some of the very early COBOL programs performing extremely mission-critical operations.

5. The Two-tier Architecture
The two-tier architecture divides an application into the following components:
Client
Server
The client implements the user interface.
The server stores the data.

6. The Two-tier Architecture (Contd.)
The following figure depicts the components of the two-tier architecture:
The communication between a Web browser and a Web server is an example of client server architecture.
Client
Two-tier Architecture
Server
Business logic
User tier
Data tier

7. The Three-tier Architecture
In the two-tier system, the actual processing of data takes place on the server. Therefore, the data has to be transported over the network. This leads to increased network stress. To overcome these problems, there was a shift from the two-tiered to the three-tiered systems.
In the three-tiered system, there is a clear separation of user-interface-control and data presentation from application-logic. Therefore, more clients are able to access a wide variety of server applications. This leads to quicker development through the reuse of pre-built business-logic components and a shorter test phase because the server-components have already been tested.

8. The Three-tier Architecture (Contd.)
The three-tiered architecture is the most popular architecture on the Web. The three-tiered architecture comprises:
The user interface, mostly a Web browser, that processes client requests in the form of HTML/DHTML pages
The data tier that stores data in the database server
The business logic tier, implemented by the Web server that uses scripting languages, such as ASP to perform tasks like form validation
All the three service layers reside separately, either on the same machine or on different machines.

9. Three-tier Architecture
The Three-tier Architecture (Contd.)
The following figure depicts the components of the three-tier architecture:
Three-tier Architecture
User Services
Business Services
Data Services
Client
Business Logic
Data Store

10. The N-tier Architecture
The n-tier architecture is an expanded model of the three-tier architecture.
A typical n-tier model consists of the following tiers:
Presentation logic tier- The presentation layer provides an interface for the end user. This layer generally consists of the windows forms and ASP pages.
Proxy tier and the distributed logic- The proxy layer provides access to distributed components in the n-tier architecture.

11. The N-tier Architecture (Contd.)
Client interface- The client interface layer represents the end-user presentation, such as the windows forms.
Business tier- The business layer is the most important part of the n-tiered architecture. It contains the business rules and data manipulation/transformation logic.
Data access tier- The data access layer is a reusable interface to the database. It contains the generic methods used to interface with the data.
Data tier- The data layer deals with storage and retrieval of information. Basically, the data tier consists of the database management systems.

12. The N-tier Architecture (Contd.)
The following figure depicts the components of the N-tier architecture:
Proxy and Distributed Logic Tier
Business Tier
Data Access
Data Tier
Presentation Tier

13. The N-tier Architecture (Contd.)
Each layer of the n-tier architecture performs specific functions. The following diagram depicts the functions performed by each layer:
N-tier architecture
View
Distributed Logic
Connects to proxy layer to send and receive requests
Presentation logic tier
Proxy tier and distributed logic
Data access tier
Data tier
Client interface
Business objects and rules
Interface with database, handles all input/output operations
Query and data storage
Business tier

14. Advantages of Using the N-tier Architecture
The n-tier application architecture helps you to create:
Robust and reliable applications for the Internet
Interoperable applications
Extensible, maintainable, and scalable applications

15. Developing an N-tier Model
To develop and integrate an n-tier model, you need to perform the following steps:
Create the data tier
Create the database, create tables in the database, and define the primary and foreign keys
Create the data access tier
Create a set of useful and specific routines to interact with the database
Create the business tier
Write useful methods that will conform to the business rules
Write codes to perform server-side data validation

16. Developing an N-tier Model (Contd.)
Set up the proxy and distributed logic tier
Add the class libraries and Web services to the project
Set up dependencies, protocols, and add references
Create the presentation tier
Create windows forms and add functionalities to the controls

17. N-tier and Enterprise Applications
Application architecture that handles persistent data and has business logic is known as enterprise architecture.
The persistent data might outlive the hardware or software that was used to collect the data.
There might be changes to the structure of data, for instance, addition of new data or reorganization of data.
The persistent data is associated with specific business logic.
This brings out the need for an enterprise application to be built on an architecture, which allows one component to be modified independently without affecting the other components. Therefore, an enterprise architecture needs to be built on the n-tier architecture.

18. N-tier and Enterprise Applications (Contd.)
The data of an enterprise application will map to the data tier of the n-tier architecture. For example, SQL can be used to store the data.
The logic to access the data can be implemented in the data access tier. For example, ADO.NET can be used to access the data.
The business logic can be implemented in the business logic tier. For example, Visual Basic .NET or C# can be used to implement the business rules.
The interpretation of the data can be implemented in the proxy and distributed logic tier. For example, C# or Visual Basic .NET can be used to implement the proxy tier.

19. N-tier and Enterprise Applications (Contd.)
The view of the data can be implemented in the presentation tier. For example, ASP.NET can be used to implement the view. A representation of the enterprise architecture is given below:
Proxy and Distributed Logic Tier
(VB.NET or C#)
Business Tier
(VB.NET or
C#)
Data Access
(ADO.NET)
Data Tier
(MS-SQL)
Presentation Tier
(ASP.NET)

20. Summary In this lesson, you learned that:
Application architectures are of the following types:
Single-tier
Two-tier
Three-tier
N-tier
In single-tier architecture, a single executable file handles all functions related to the user, business, and data service layers.

21. Summary (Contd.)
Two-tier architecture comprises the following components:
Client
Server
In the two-tier architecture, the actual processing of data takes place on the server. Therefore, the data has to be transported over the network. This leads to increased network stress.
The three-tiered architecture comprises:
The user interface, mostly a Web browser, that processes client requests in the form of HTML/DHTML pages
The data tier that stores data in the database server

22. Summary (Contd.)
The business logic tier, implemented by the Web server that uses scripting languages, such as ASP to perform tasks like form validation
A typical n-tier model consists of the following tiers:
Presentation logic tier
Proxy tier and the distributed logic
Client interface
Business tier
Data access tier
Data tier

23. Summary (Contd.)
The data layer deals with storage and retrieval of information. The data tier consists of the database management systems.
The presentation layer provides an interface for the end user into the application. This layer generally consists of the windows forms and ASP pages.
The proxy layer provides access to the next tier in the multi-tiered system.
The client interface layer represents the end-user presentation, such as the windows forms.
The business layer is the most important part of the n-tiered architecture. It contains the business rules and data manipulation/transformation logic.

24. Summary (Contd.)
The data access layer is a reusable interface to the database. It contains the generic methods used to interface with the data.
Using n-tier application architecture, you can create:
Robust and reliable applications for the Internet
Extensible, maintainable, and scalable applications
Interoperable applications
Application architecture that handles persistent data and has business logic is known as enterprise architecture.
The persistent data might outlive the hardware or software that was used to collect the data.

25. Summary (Contd.)
The persistent data is associated with specific business logic.
The data of an enterprise application will map to the data tier of the n-tier architecture. For example, SQL can be used to store the data.
The logic to access the data can be implemented in the data access tier. For example, ADO.NET can be used to access the data.
The business logic can be implemented in the business logic tier. For example, Visual Basic .NET or C# can be used to implement the business rules.
The interpretation of the data can be implemented in the proxy and distributed logic tier. For example, C# or Visual Basic .NET can be used to implement the proxy tier.

26. Summary (Contd.)
The view of the data can be implemented in the presentation tier. For example, ASP.NET can be used to implement the view.