The 3-tier
software model was introduced in 1990’s as a remedy for the limitations in
2-tier architecture. In this model a third tier/layer is engaged, known as the
middle tier server (Application tier/business logic tier), located between the
Data Management (server) and the User Interface (client) constituents, mainly
to perform corporate business logic and regulations through Process Management
by accommodating hundreds of users (comparatively 2-tier model has user base of
100) to offer functionalities as queuing, application execution, and database
staging (Client/Server Architectures,2011).
Usually a
three tier architecture is implemented if there’s a necessitate for an
efficient distributed client/server devise to offer ” increased performance, flexibility, maintainability, reusability, and scalability, while hiding the complexity
of distributed processing from the user” (Client/Server
Architectures,2011).
This
offers trouble-free deployment over the network and can be managed well due to
the centralized behavior of servers. The protocol of communication between
client/server is as follows;
The client calls for the business logic on the server, the
business logic on the behalf of the client accesses the database (Client/Server
Architectures,2011).
Basic
functionalities of the layers are;
- Presentation
Tier -
Uses a business tier driven interface with classes and objects, e.g- in
ASP.NET comprises of objects like ASPX pages, user and server controls etc.(Yang
2004)
- Middle Tier
(Business Logic tier) - This basically acts as an
intermediate in the communication between presentation and data tier by
retrieving modifying data from the database according to business logic
and forwarding it to the presentation layer to display results to the
user. Often the client request balancing is done via tools as ORB and
Transaction processing-TP. In the case of ADO.NET it uses SqlClient or
OleDb objects to retrieve and modify data from SQL server or Access, by
forwarding the information to the presentation layer with DataReader or
Dataset object, or a custom collection object (Yang, 2004).
- Data Tier-Represents the
database with data access procedures e.g-Oracle, mySQL or even XML. .(Yang
2004)
The
3-tier architecture endorses a user system where a whole set of user services
are offered (session, text and dialog input, display management) and it also
substitutes several server calls for multiple SQL queries and updates,
enhancing its performance compared to the 2-tier model (slideshare, 2011).
Employment
of middle tier provisions Process Management services as process development
and performance, process monitoring and resourcing of services which are shared
by many applications and also it offers database management via data and file
services which can be developed without the usage of proprietary DBMS languages
(Client/Server Architectures,2011).
Usually
3-tier thin client model is represented in some web applications, comprising a
client application which connects to web servers as Apache or IIS, CGI based
technology through web-requests using a web browser. Then the web browser
communicates with the data tier/database servers like MySQL, Oracle etc, also
thick client applications use technologies as CORBA and DCOM (ASKESIS, 2010).
Bibliography
o slideshare.
(2011). Client Server Architecture. [Online]. Available from:
http://www.slideshare.net/suks_87/client-server-architecture-presentation.
[Accessed: 20th January 2011]
o Yang.
(2004). What is n-Tier Architecture?. [Online].Available from:
http://www.developerfusion.com/article/3058/boosting-your-net-application-performance/2/.
[Accessed: 25th January 2011]
o ASKESIS.
(2004). Client server computing. [Online].Available from:
http://www.askesis.nl/en/tutorial/docs/J2EE/body.html. [Accessed: 25th January
2011]
