In software engineering The term software engineering first appeared in the 1968 NATO Software Engineering Conference and was meant to provoke thought regarding the current "software crisis" at the time. Since then, it has continued as a profession and field of study dedicated to creating software that is of higher quality, more affordable, maintainable, and, a web application or webapp ^[1] is an application Application software is any tool that functions and is operated by means of a computer, with the purpose of supporting or improving the software user's work. In other words, it is the subclass of computer software that employs the capabilities of a computer directly and thoroughly to a task that the user wishes to perform. This should be that is accessed via web browser A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web. An information resource is identified by a Uniform Resource Identifier and may be a web page, image, video, or other piece of content. Hyperlinks present in resources enable users to easily navigate their browsers to over a network such as the Internet The Internet is a global system of interconnected computer networks that use the standardized Internet Protocol Suite . It is a network of networks that consists of millions of private and public, academic, business, and government networks of local to global scope that are linked by copper wires, fiber-optic cables, wireless connections, and or an intranet An intranet is a private computer network that uses Internet technologies to securely share any part of an organization's information or operational systems with its employees. Sometimes the term refers only to the organization's internal website, but often it is a more extensive part of the organization's computer infrastructure and private. It is also a computer software application that is coded in a browser-supported language (such as HTML HTML, an initialism for Hypertext Mark-up Language, is the predominant markup language for web pages. It provides a means to describe the structure of text-based information in a document—by denoting certain text as links, headings, paragraphs, lists, etc.—and to supplement that text with interactive forms, embedded images, and other objects, JavaScript JavaScript is a scripting language used to enable programmatic access to objects within other applications. It is primarily used in the form of client-side JavaScript for the development of dynamic websites. JavaScript is a dialect of the ECMAScript standard and is characterized as a dynamic, weakly typed, prototype-based language with first-class, Java Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities. Java applications are typically compiled to bytecode that can run, etc.) and reliant on a common web browser to render the application executable In computing, an executable causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a file that only contains data. Files that contain instructions for an interpreter or virtual machine may be considered executables, but are more specifically called scripts or bytecode. Executables are also called &.

Web applications are popular due to the ubiquity of web browsers, and the convenience of using a web browser as a client A client is an application or system that accesses a remote service on another computer system, known as a server, by way of a network. The term was first applied to devices that were not capable of running their own stand-alone programs, but could interact with remote computers via a network. These dumb terminals were clients of the time-sharing, sometimes called a thin client A thin client is a client computer or client software in client-server architecture networks which depends primarily on the central server for processing activities, and mainly focuses on conveying input and output between the user and the remote server. In contrast, a thick or fat client does as much processing as possible and passes only data. 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. Common web applications include webmail Webmail is an e-mail service intended to be primarily accessed via a web browser, as opposed to through an e-mail client, such as Microsoft Outlook, Mozilla's Thunderbird, or Apple Inc.'s Mail. Very popular webmail providers include Gmail, Yahoo! Mail, Hotmail and AOL, online retail sales Retailing consists of the sale of goods or merchandise from a fixed location, such as a department store, boutique or kiosk, or by post, in small or individual lots for direct consumption by the purchaser. Retailing may include subordinated services, such as delivery. Purchasers may be individuals or businesses. In commerce, a "retailer", online auctions The online auction business model is one in which participants bid for products and services over the Internet. The functionality of buying and selling in an auction format is made possible through auction software which regulates the various processes involved, wikis A wiki is a website that uses wiki software, allowing the easy creation and editing of any number of interlinked Web pages, using a simplified markup language or a WYSIWYG text editor, within the browser. Wikis are often used to create collaborative websites, to power community websites, and for note taking. The collaborative encyclopedia and many other functions.

History

In earlier types of client-server Client-server computing or networking is a distributed application architecture that partitions tasks or work loads between service providers and service requesters, called clients. Often clients and servers operate over a computer network on separate hardware. A server is a high-performance host that is a registering unit and shares its resources computing, each application had its own client program which served as its user interface The user interface (also known as human computer interface or man-machine interface ) is the aggregate of means by which people—the users—interact with the system—a particular machine, device, computer program or other complex tool. The user interface provides means of: and had to be separately installed on each user's personal computer A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator. 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 Technical support is a range of services providing assistance with technology products such as mobile phones, televisions, computers, or other electronic or mechanical goods. In general, technical support services attempt to help the user solve specific problems with a product—rather than providing training, customization, or other support cost and decreasing productivity Productivity refers to metrics and measures of output from production processes, per unit of input. Labor productivity, for example, is typically measured as a ratio of output per labor-hour, an input. Productivity may be conceived of as a metrics of the technical or engineering efficiency of production. As such quantitative metrics of input, and.

In contrast, web applications use web documents A PDF document requested from SFTP or SMTP protocols, for example, is a web document, but not a web page written in a standard format such as HTML HTML, an initialism for Hypertext Mark-up Language, is the predominant markup language for web pages. It provides a means to describe the structure of text-based information in a document—by denoting certain text as links, headings, paragraphs, lists, etc.—and to supplement that text with interactive forms, embedded images, and other objects (and more recently XHTML The Extensible Hypertext Markup Language, or XHTML, is a markup language that has the same depth of expression as HTML, but also conforms to XML syntax), which are supported by a variety of web browsers.

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 A webform on a web page allows a user to enter data that is sent to a server for processing. Webforms resemble paper forms because internet users fill out the forms using checkboxes, radio buttons, or text fields. For example, webforms can be used to enter shipping or credit card data to order a product or can be used to retrieve data 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.

In 1995, Netscape introduced a client-side scripting Client-side scripting generally refers to the class of computer programs on the web that are executed client-side, by the user's web browser, instead of server-side . This type of computer programming is an important part of the Dynamic HTML (DHTML) concept, enabling web pages to be scripted; that is, to have different and changing content called JavaScript JavaScript is a scripting language used to enable programmatic access to objects within other applications. It is primarily used in the form of client-side JavaScript for the development of dynamic websites. JavaScript is a dialect of the ECMAScript standard and is characterized as a dynamic, weakly typed, prototype-based language with first-class, which allowed programmers to add some dynamic elements to the user interface that ran on the client side. Until then, all the data had to be sent to the server for processing, and the results were delivered through static HTML pages sent back to the client.

In 1996, Macromedia introduced Flash Adobe Flash is a multimedia platform originally acquired by Macromedia and currently developed and distributed by Adobe Systems. Since its introduction in 1996, Flash has become a popular method for adding animation and interactivity to web pages. Flash is commonly used to create animation, advertisements, and various web page components, to, a vector animation player that could be added to browsers as a plugin In computing, a plug-in consists of a computer program that interacts with a host application (a web browser or an email client, for example) to provide a certain, usually very specific, function "on demand". Often, add-on is considered the general term comprising plugins, extensions, and themes as subcategories[citation needed] to embed animations on the web pages. It allowed the use of a scripting language to program interactions on the client side with no need to communicate with the server.

In 1999, the "web application" concept was introduced in the Java language in the Servlet Specification version 2.2. [2.1?]. ^[1][2] At that time both JavaScript JavaScript is a scripting language used to enable programmatic access to objects within other applications. It is primarily used in the form of client-side JavaScript for the development of dynamic websites. JavaScript is a dialect of the ECMAScript standard and is characterized as a dynamic, weakly typed, prototype-based language with first-class and XML XML is a general-purpose specification for creating custom markup languages. It is classified as an extensible language, because it allows the user to define the mark-up elements had already been developed, but AJAX Ajax, sometimes written as AJAX , is a group of interrelated web development techniques used on the client-side to create interactive web applications or rich Internet applications. With Ajax, web applications can retrieve data from the server asynchronously in the background without interfering with the display and behavior of the existing page had still not yet been coined and the XMLHttpRequest object had only been recently introduced on Internet Explorer 5 as an ActiveX object. ^[3]

In 2005, AJAX was coined, and applications like Gmail Gmail is a free webmail, POP3 and IMAP service provided by Google. In the United Kingdom and Germany it is officially called Google Mail started to make their client sides more and more interactive.

Interface

The web interface places very few limits on client functionality. Through Java Java refers to a number of computer software products and specifications from Sun Microsystems that together provide a system for developing application software and deploying it in a cross-platform environment. Java is used in a wide variety of computing platforms from embedded devices and mobile phones on the low end, to enterprise servers and, JavaScript JavaScript is a scripting language used to enable programmatic access to objects within other applications. It is primarily used in the form of client-side JavaScript for the development of dynamic websites. JavaScript is a dialect of the ECMAScript standard and is characterized as a dynamic, weakly typed, prototype-based language with first-class, DHTML Dynamic HTML, or DHTML, is a collection of technologies used together to create interactive and animated web sites by using a combination of a static markup language , a client-side scripting language (such as JavaScript), a presentation definition language (such as CSS), and the Document Object Model, Flash Adobe Flash is a multimedia platform originally acquired by Macromedia and currently developed and distributed by Adobe Systems. Since its introduction in 1996, Flash has become a popular method for adding animation and interactivity to web pages. Flash is commonly used to create animation, advertisements, and various web page components, to and other technologies, application-specific methods such as drawing on the screen, playing audio, and access to the keyboard and mouse are all possible. Many services have worked to combine all of these into a more familiar interface that adopts the appearance of an operating system. General purpose techniques such as drag and drop In computer graphical user interfaces, drag-and-drop or DnD is the action of clicking on a virtual object and dragging it to a different location or onto another virtual object. In general, it can be used to invoke many kinds of actions, or create various types of associations between two abstract objects 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. Recently, technologies have been developed to coordinate client-side scripting with server-side technologies such as PHP PHP is a scripting language originally designed for producing dynamic web pages. It has evolved to include a command line interface capability and can be used in standalone graphical applications. Ajax Ajax, sometimes written as AJAX , is a group of interrelated web development techniques used on the client-side to create interactive web applications or rich Internet applications. With Ajax, web applications can retrieve data from the server asynchronously in the background without interfering with the display and behavior of the existing page, a web development technique using a combination of various technologies, is an example of technology which creates a more interactive experience.

Technical considerations

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 Microsoft Windows is a series of software operating systems and graphical user interfaces produced by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal, Mac OS X Mac OS X is a line of computer operating systems developed, marketed, and sold by Apple Inc., and since 2002 has been included with all new Macintosh computer systems. It is the successor to Mac OS 9, the final release of the "classic" Mac OS, which had been Apple's primary operating system since 1984. Mac OS X, whose "X", Linux Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed by anyone under the terms of the GNU GPL and other free, and other operating systems An operating system is an interface between hardware and user; an OS is responsible for the management and coordination of activities and the sharing of the resources of the computer. The operating system acts as a host for computing applications that are run on the machine. As a host, one of the purposes of an operating system is to handle the, the application can be written once and deployed almost anywhere. However, inconsistent implementations of the HTML HTML, an initialism for Hypertext Mark-up Language, is the predominant markup language for web pages. It provides a means to describe the structure of text-based information in a document—by denoting certain text as links, headings, paragraphs, lists, etc.—and to supplement that text with interactive forms, embedded images, and other objects, CSS Cascading Style Sheets is a style sheet language used to describe the presentation (that is, the look and formatting) of a document written in a markup language. Its most common application is to style web pages written in HTML and XHTML, but the language can be applied to any kind of XML document, including SVG and XUL, DOM The Document Object Model is a cross-platform and language-independent convention for representing and interacting with objects in HTML, XHTML and XML documents. Objects under the DOM (also sometimes called "Elements") may be specified and addressed according to the syntax and rules of the programming language used to manipulate them 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 approach is to use Adobe Flash Adobe Flash is a multimedia platform originally acquired by Macromedia and currently developed and distributed by Adobe Systems. Since its introduction in 1996, Flash has become a popular method for adding animation and interactivity to web pages. Flash is commonly used to create animation, advertisements, and various web page components, to or Java applets A Java applet is an applet delivered to the users in the form of Java bytecode. Java applets can run in a Web browser using a Java Virtual Machine , or in Sun's AppletViewer, a stand-alone tool for testing applets. Java applets were introduced in the first version of the Java language in 1995. Java applets are usually written in the Java 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 Internet Application" (RIA).

Structure

Applications are usually broken into logical chunks called "tiers", where every tier is assigned a role.^[4] Traditional applications consist only of 1 tier, which resides on the client machine, but web applications lend themselves to a n-tiered approach by nature.^[4] Though many variations are possible, the most common structure is the three-tiered application.^[4] In its most common form, the three tiers are called presentation, application and storage, in this order. A web browser is the first tier (presentation), an engine using some dynamic Web content technology (such as ASP, ASP.NET, CGI, ColdFusion, JSP/Java, PHP, Perl, Python, Ruby on Rails or Struts2) is the middle tier (application logic), and a database is the third tier (storage).^[4] 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.

For more complex applications, a 3-tier solution may fall short, and you may need a n-tiered approach, where the greatest benefit is breaking the business logic, which resides on the application tier, into a more fine-grained model.^[4] For example, creating a separate business logic tier. Or adding an integration tier that separates the data tier from the rest of tiers by providing an easy-to-use interface to access the data.^[4] For example, you would access the client data by calling a "list_clients()" function instead of making a SQL query directly against the client table on the database. That allows you to replace the underlying database without changing the other tiers.^[4]

There are some who view a web application as a two-tier architecture. This can be a "smart" client that performs all the work and queries a "dumb" server, or a "dumb" client that relies on a "smart" server. ^[4] The client would handle the presentation tier, the server would have the database (storage tier), and the business logic (application tier) would be on one of them or on both. ^[4] While this increases the scalability of the applications and separates the display and the database, it still doesn't allow for true specialization of layers, so most applications will outgrow this model.^[4]

Business use

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 as an 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 simpler, 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

The Web Application Security Consortium [1] (WASC) and OWASP are projects developed with the intention of documenting how to avoid security problems in web applications. A web application security scanner is specialized software for detecting security problems in web applications.

Applications

Browser applications typically include simple office software (word processors, online spreadsheets, and presentation tools), with Google Docs being the most notable example, and can also include more advanced applications such as project management, computer-aided design, video editing and point-of-sale

Benefits

Browser applications typically require little or no disk space on the client, upgrade automatically with new features, integrate easily into other web procedures, such as email and searching. They also provide cross-platform compatibility (i.e., Windows, Mac, Linux, etc.) because they operate within a web browser window.

Drawbacks

Standards compliance is an issue with any non-typical office document creator, which causes problems when file sharing and collaboration becomes critical. Also, browser applications rely on application files accessed on remote servers through the Internet. Therefore, when connection is interrupted, the application is no longer usable. Google Gears is a platform to ameliorate this issue and improve the usability of browser applications.

See also

• Cascading style sheets (CSS)
• Content management framework
• Dynamic HTML (DHTML)
• Hypertext Markup Language (HTML)
• JavaServer Pages (JSP)
• List of web application frameworks
• Scalable Vector Graphics (SVG)
• Software as a service (SaaS)
• Software development
• WAR file
• Web 2.0
• Web services
• World Wide Web Consortium (Web standards)
• XRX (web application architecture)

References

1. ^ ^{a b} Alex Chaffee (2000-08-17). "What is a web application (or "webapp")?". http://www.jguru.com/faq/view.jsp?EID=129328. Retrieved on 2008-07-27.
2. ^ James Duncan Davidson, Danny Coward (17-12-1999). Java Servlet Specification ("Specification") Version: 2.2 Final Release. Sun Microsystems. pp. 43–46. http://java.sun.com/products/servlet/download.html. Retrieved on 2008-07-27.
3. ^ "Dynamic HTML and XML: The XMLHttpRequest Object". Apple Inc. http://developer.apple.com/internet/webcontent/xmlhttpreq.html. Retrieved on 2008-06-25.
4. ^ ^{a b c d e f g h i j} Jeremy Petersen. "Benefits of using the n-tiered approach for web applications". http://www.adobe.com/devnet/coldfusion/articles/ntier.html.

External links

• HTML 5 Draft recommendation, changes to HTML and related APIs to ease authoring of web-based applications.
• The Other Road Ahead — An article arguing that the future lies on the server, not rich interfaces on the client
• Web Applications at the Open Directory Project

Categories: Software architecture | Web applications | Web development

See Also:

• Web Application
• Mail (Application)
• Application Software
• Mashup (Web Application Hybrid)
• Feedreader (Windows Application)

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