Understanding A Basic N Tier E-Commerce Site
I am sure you must have heard of
"Ecommerce". And readers who have used an Ecommerce application
(Rediff, Indiamarkets, Bazee) will readily accept that the Internet and its
Ecommerce Revolution is not just hype but an environment which brings
individuals and organisations together in newer and exciting ways.
Ecommerce applications are either in B2B, B2C segments.
These Applications can also be classified as Mcommerce where the user uses a
mobile phone to access Internet sites.
This article
discusses tools and services to develop such applications.
In any application, complex or simple, we talk about the facilities or
services which we are to be considered. Each service has a particular role in
the application namely Database Services, User Interface Services, Mail
Services, Print Services, Help Services etc.
The presentation tier is responsible for providing the services the application needs to allow the user to view and manipulate the application. Simply put it presents an easy interface to the user. In 2 Tier (Presentaion layer directly talks with database) it could be any of the common front ends namely Visual Basic, Powerbuider, Developer 2000 etc.. In a Web oriented application, the presentation tier will be of HTML. With HTML, we can create static web pages. Static pages means we can display information but it will not give us the features to make it interactive. Web Interactivity can be provided by the following tools namely Scripting Tools, Applets, WML script.
Scripting language allows us to make interactive web pages. So for asking any information from user, validating the information on client side will be done by scripting language and HTML as a combination. VBscript and Javascript are two popular scripting languages. Making use of VBScript has a specific disadvantage that it becomes dependent on browser. All the browsers do not support VBScript. So generally, if we want to make a site independent of browser and operating system, on presentation layer we should go in for the combination of HTML and JavaScript.
Applet is a program which can be executed from browser. Applets also can be used in combination with HTML to provide Interactivity. To write an applet, the developer should be in a position to write Java code.
The Business Tier is the most complicated
Layer.To understand how the business tier works, let us understand what it is
going to contain.Any business has a set of predefined set of rules.These rules
can be very simple such as "in the month of Diwali there has to be 10%
discount" or a complex rule can set 10% discount for purchases belowRs.
1000, 15% discount for purchases between 1001 to 2500 Rs and so on.Since all
business operations follow specified procedures and rules, then it follows that
all software that drives that business must follow the exact same rules. The
software implementationof these procedures is called Business Rules or Business
Logic. Because we live in an object-oriented world, we implement these business
rules in business objects. (COM/DCOM, EJB)
As the
complexity of business logic increases this tier gets divided into multiple
tiers and it is then called N-Tier application.
For
Microsoft platform, our business layer can use applications like ASP(Active
Server Pages) or COM/DCOM.
For Java platform, it
includes server site programming tools like Servlet (ServerSide Applet), JSP
(Java Server Pages) and EJB (Enterprise Java Beans). Recently Java platform is
becoming popular as compared to Microsoft because of robust application
development, Platform Neutral behaviour and many other advantages.
The database tier is the simplest one to
understand. It is responsible for querying and manipulating the database under
instructions from the business tier. Common database applications are SQL
Server, Oracle etc.
One of the key things to remember in
three tier application development is Presentation Tier should never talk to
Database Tier. Generally for any application, business logic changes less
frequently than the presentation layer. If you allow presentation layer to
change database, the chances of errors and corrupting the database tier are
fairly high. Making both layers connecting also means that presentation layer
will require lots of modifications if database is changed.
The author Ms. Vaishali
Tapaswi is Director, Fands Infotrainers and can be
reached at