Three Tier Client Server Architecture (M3.3)

A 3 Tier Architecture in DBMS is the most popular client server architecture in DBMS in which the development and maintenance of functional processes, logic, data access, data storage, and user interface is done independently as separate modules.

3-Tier database Architecture design is an extension of the 2-tier client-server architecture. A 3-tier architecture has the following layers:

1. Presentation layer (your PC, Tablet, Mobile, etc.)
2. Application layer (server)
3. Database Server

The chief benefit of three-tier architecture is that because each tier runs on its own infrastructure, each tier can be developed simultaneously by a separate development team, and can be updated or scaled as needed without impacting the other tiers.

Presentation tier

• The presentation tier is the user interface and communication layer of the application, where the end user interacts with the application. 
• Its main purpose is to display information to and collect information from the user. 
• This top-level tier can run on a web browser, as desktop application, or a graphical user interface (GUI), 
• For example. Web presentation tiers are usually developed using HTML, CSS and JavaScript. Desktop applications can be written in a variety of languages depending on the platform.

Application tier

• The application tier, also known as the logic tier or middle tier, is the heart of the application. 
• In this tier, information collected in the presentation tier is processed - sometimes against other information in the data tier - using business logic, a specific set of business rules. 
• The application tier can also add, delete or modify data in the data tier.

The application tier is typically developed using Python, Java, Perl, PHP or Ruby, and communicates with the data tier using API calls. 

Data tier

• The data tier, sometimes called database tier, data access tier or back-end, is where the information processed by the application is stored and managed.
• This can be a relational database management system such as PostgreSQL, MySQL, MariaDB, Oracle, DB2, Informix or Microsoft SQL Server, or in a NoSQL Database server such as Cassandra, CouchDB or MongoDB. 

In a three-tier application, all communication goes through the application tier. The presentation tier and the data tier cannot communicate directly with one another.

The goal of Three Tier client-server architecture is:

• To separate the user applications and physical database
• To support DBMS characteristics
• Program-data independence
• Supporting multiple views of the data

Benefits of three-tier architecture

Again, the chief benefit of three-tier architecture its logical and physical separation of functionality. Each tier can run on a separate operating system and server platform - e.g., web server, application server, database server - that best fits its functional requirements. And each tier runs on at least one dedicated server hardware or virtual server, so the services of each tier can be customized and optimized without impact the other tiers. 

Other benefits (compared to single- or two-tier architecture) include:

• Faster development: Because each tier can be developed simultaneously by different teams, an organization can bring the application to market faster, and programmers can use the latest and best languages and tools for each tier.
• Improved scalability: Any tier can be scaled independently of the others as needed.
• Improved reliability: An outage in one tier is less likely to impact the availability or performance of the other tiers.
• Improved security: Because the presentation tier and data tier can't communicate directly, a well-designed application tier can function as a sort of internal firewall, preventing SQL injections and other malicious exploits.

 A 'layer' refers to a functional division of the software, but a 'tier' refers to a functional division of the software that runs on infrastructure separate from the other divisions. The Contacts app on your phone, for example, is a three-layer application, but a single-tier application, because all three layers run on your phone.