3 tier architecture

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3-Tier ArchitectureLecture-2Subject Web
EngineeringPresented By Tahir khan
Roll1049BSIT(Hon)IT 5th morningteaching by
Inam Ul Haq
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3-Tier Architectures
What does Three-Tier Architecture mean?
A three-tier architecture is a client-server
architecture in which the functional process,
data access, computer data storage and user
interface are developed and maintained as
independent modules on separate platforms.
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3-Tier Architectures(Cont)

• (A 3-tier architecture is one which has a client
  tier, a middle tier, and a database tier)
• The database tier manages the database
• The middle tier contains most of the logic and
  communicates between the other tiers
• The client tier is the interface between the user
  and the system
• Definition An n-tier architecture is one which
  has n tiers, usually including a database tier, a
  client tier, and n-2 tiers in between.

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3-Tier Architectures

• Presentation Tier Occupies the top level and
  displays information related to services
  available on a website. This tier communicates
  with other tiers by sending results to the
  browser and other tiers in the network.
• Application Tier Also called the middle tier,
  logic tier, business logic or logic tier, this
  tier is pulled from the presentation tier. It
  controls application functionality by performing
  detailed processing.
• Data Tier Houses database servers where
  information is stored and retrieved. Data in this
  tier is kept independent of application servers
  or business logic.

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Where are these Tiers?

• Physical partitioning of applications
• terminal(tier1), minicomputer(tier2),
  mainframes(tier3)
• Logical partitioning of applications
• 2-tier
• client(tier 1) a big chunk of application
• server(tier 2) DBMS
• 3-tier
• client(tier1) GUI
• application server(tier2) all chunk of business
  applications
• server(tier3) DBMS

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Why 3-Tier Architecture ?

• Needs of new worlds applications
• Business will increasingly compete being the
  first to market with new electronic goods and
  services
• Companies will create virtual corporations
  through alliances with a shifting set of partners
• Roles and relationships btw. enterprises will
  shift frequently as industries realign
• Reasons
• Meets the requirements of large-scale internet
  and intranet client/server applications
• Is easier to manage and deploy on the network
• most of code runs on the servers, especially with
  zero-footprint technologies like Java applets
• Minimizes network interchanges by creating
  abstract levels of service
• Provides better security
• by not exposing the database schema to the client
• by enabling more fine-grained authorization on
  the server

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Another 3-Tier Model

• You could also think of this as a 4-tier
  architecture
• The database management system (DBMS)
• A persistence manager
• The main application software
• A GUI (thin or thick)

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• Web And Mobile Applications
• Web applications are very common examples of
  3-tier applications
• The presentation tier consists of HTML, CSS and
  JavaScript
• The application logic tier runs on a web server
  in form of Java Servlets, JSP, ASP.NET, PHP,
  Ruby, Python etc.,
• and the data tier consists of a database of some
  kind (mysql, postgresql, a noSQL database etc.).
  Here is a diagram of a typical 3 tier web
  application

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Actually, it is the same principle with mobile
applications and are not standalone applications.
A mobile application that connects to a server
typically connects to a web server and sends and
receives data. Here is a diagram of a typical 3
tier mobile application
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Rich Internet Applications (RIA) In the first
generations of web applications a lot of the
HTML, and parts of the CSS and JavaScript was
generated by scripts running on the web server.
When a browser requests a certain page on the web
server, a script was executed on the web server
which generated the HTML, CSS and JavaScript for
that page. Today the world is moving to rich
internet applications (RIA). RIA also uses a 3
tier architecture, but all the HTML, CSS and
JavaScript is generated in the browser. The
browser has to download the initial HTML, CSs and
JavaScript files once, but after that the RIA
client only exchanges data with the web server.
No HTML, CSS or JavaScript is sent forth and back
(unless that is part of the data, like with an
article that contains HTML codes). RIA
applications are explained in more detail in the
next text in the software architecture trail.
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Web Application Advantages The purpose of N tier
architecture is to insulate the different layers
of the application from each other. The GUI
client doesn't know how the server is working
internally, and the server doesn't know how the
database server works internally etc. They just
communicate via standard interfaces. Web
applications especially have another advantage.
If you make updates to the GUI client or the
application logic running on the server, all
clients get the latest updates the next time they
access the application. The browser downloads the
updated client, and the updated client accesses
the updated server.
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Questions

• Quote an example of 1 tier, 2 tiers and 3 tiers
• How 3-tier is more secure and reusable?
• Famous websites such as Amazon and BBC.com have
  used multi tier architecture, explore yourself