Web Design & Development Guide
Rich Internet Applications
Web application framework
Web application development
software engineering, a Web application or webapp is
application that is accessed via web over a network such as the Internet
or an intranet.
Web applications are popular due to the ubiquity of a client, sometimes
called a thin client. The ability to update and maintain Web applications
without distributing and installing software on potentially thousands of client
computers is a key reason for their popularity. Web applications are used to
implement Webmail, online retail sales, online auctions, wikis, discussion
boards, Weblogs, MMORPGs and
many other functions.
In earlier types of
client-server computing, each application had its own client program which
served as its user interface and had to be separately installed on each user's
personal computer. An upgrade to the server part of the application would
typically require an upgrade to the clients installed on each user workstation,
adding to the support cost and decreasing productivity.
In contrast, Web applications dynamically generate a series of Web documents
in a standard format supported by common browsers such as HTML/XHTML.
included to add dynamic elements to the user interface. Generally, each
individual Web page is delivered to the client as a static document, but the
sequence of pages can provide an interactive experience, as user input is
returned through Web form elements embedded in the page markup. During the session, the Web
browser interprets and displays the pages, and acts as the universal
client for any Web application.
The Web interface places very few limits on client functionality. Through
methods such as drawing on the screen, playing audio, and access to the keyboard
and mouse are all possible. General purpose techniques such as drag and drop are
also supported by these technologies. Web developers often use client-side
scripting to add functionality, especially to create an interactive experience
that does not require page reloading (which many users find disruptive).
Recently, technologies have been developed to coordinate client-side scripting
with server-side technologies such as PHP.
Ajax, a web development technique using a combination of various
technologies, is an example of technology which creates a more interactive
A significant advantage of building Web applications to support standard
browser features is that they should perform as specified regardless of the
operating system or OS version installed on a given client. Rather than creating
clients for MS Windows, Mac OS X, GNU/Linux, and other operating systems, the
application can be written once and deployed almost anywhere. However,
inconsistent implementations of the HTML, CSS, DOM and other browser specifications can cause problems in web application
development and support. Additionally, the ability of users to customize many of
the display settings of their browser (such as selecting different font sizes,
colors, and typefaces, or disabling scripting support) can interfere with
consistent implementation of a Web application.
Another (less common) approach is to use
applets to provide some or all of the user interface. Since most Web
browsers include support for these technologies (usually through plug-ins),
Flash- or Java-based applications can be implemented with much of the same ease
of deployment. Because they allow the programmer greater control over the
interface, they bypass many browser-configuration issues, although
incompatibilities between Java or Flash implementations on the client can
introduce different complications. Because of their architectural similarities
to traditional client-server applications, with a somewhat "thick" client, there
is some dispute over whether to call systems of this sort "Web applications"; an
alternative term is "Rich
Though many variations are possible, a Web application is commonly structured
three-tiered application. In its most common form, a Web browser is the first
tier, an engine using some dynamic Web content technology (such as ASP, ASP.NET,
CGI, ColdFusion, JSP/Java, PHP, Python, or Ruby On Rails) is the middle tier, and a database is the third tier. The Web
browser sends requests to the middle tier, which services them by making queries
and updates against the database and generates a user interface.
An emerging strategy for application software companies is to provide Web
access to software previously distributed as local applications. Depending on
the type of application, it may require the development of an entirely different
browser-based interface, or merely adapting an existing application to use
different presentation technology. These programs allow the user to pay a
monthly or yearly fee for use of a software application without having to
install it on a local hard drive. A company which follows this strategy is known
application service provider (ASP), and ASPs are currently receiving much
attention in the software industry.
Writing Web applications
There are many
Web application frameworks which facilitate rapid application development by
allowing the programmer to define a high-level description of the program. In
addition, there is potential for the development of applications on
Internet Operating Systems, although currently there are not many viable
platforms that fit this model.
The use of Web application frameworks can often reduce the number of errors
in a program, both by making the code more simple, and by allowing one team to
concentrate just on the framework. In applications which are exposed to constant
hacking attempts on the Internet, security-related problems caused by errors
in the program are a big issue. Frameworks may also promote the use of best
practices such as
GET after POST
Web Application Security Consortium (WASC),
CGI Security, and
OWASP are projects developed with the intention of documenting how to avoid
security problems in Web applications.