Rich Internet application

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Rich Internet applications (RIA) are web applications that have the features and functionality of traditional desktop applications. RIAs typically transfer the processing necessary for the user interface to the web client but keep the bulk of the data (i.e maintaining the state of the program, the data etc) back on the application server.

RIAs typically:

  • run in a web browser, or do not require software installation
  • run locally in a secure environment called a sandbox
  • can be "occasionally connected" wandering in and out of hot-spots or from office to office.

Contents

[edit] History of RIAs

The term "Rich Internet application" was introduced in a Macromedia whitepaper in March 2002, though the concept had been around for a number of years before that under different names such as:

[edit] Comparison to standard web applications

Traditional web applications centered all activity around a client-server architecture with a thin client. Under this system all processing is done on the server, and the client is only used to display static (in this case HTML) content. The biggest drawback with this system is that all interaction with the application must pass through the server, which requires data to be sent to the server, the server to respond, and the page to be reloaded on the client with the response. By using a client side technology which can execute instructions on the client's computer, RIAs can circumvent this slow and synchronous loop for many user interactions. This difference is somewhat analogous to the difference between "terminal and mainframe" and Client-server/Fat client approaches.

Internet standards have evolved slowly and continually over time to accommodate these techniques, so it is hard to draw a strict line between what constitutes an RIA and what does not. But all RIAs share one characteristic: they introduce an intermediate layer of code, often called a client engine, between the user and the server. This client engine is usually downloaded at the beginning of the application, and may be supplemented by further code downloads as the application progresses. The client engine acts as an extension of the browser, and usually takes over responsibility for rendering the application's user interface and for server communication.

What can be done in an RIA may be limited by the capabilities of the system used on the client. But in general, the client engine is programmed to perform application functions that its designer believes will enhance some aspect the user interface, or improve its responsiveness when handling certain user interactions, compared to a standard Web browser implementation. Also, while simply adding a client engine does not force an application to depart from the normal synchronous pattern of interactions between browser and server, in most RIAs the client engine performs additional asynchronous communications with servers.

[edit] Benefits

Because RIAs employ a client engine to interact with the user, they are:

  • Richer. They can offer user-interface behaviors not obtainable using only the HTML widgets available to standard browser-based Web applications. This richer functionality may include anything that can be implemented in the technology being used on the client side, including drag and drop, using a slider to change data, calculations performed only by the client and which do not need to be sent back to the server (e.g. an insurance rate calculator), etc.
  • More responsive. The interface behaviors are typically much more responsive than those of a standard Web browser that must always interact with the server.

The most sophisticated examples of RIAs exhibit a look and feel approaching that of a desktop environment. Using a client engine can also produce other performance benefits:

  • Client/Server balance. The demand for client and server computing resources is better balanced, so that the Web server need not be the workhorse that it is with a traditional Web application. This frees server resources, allowing the same server hardware to handle more client sessions concurrently.
  • Asynchronous communication. The client engine can interact with the server asynchronously -- that is, without waiting for the user to perform an interface action like clicking on a button or link. This option allows RIA designers to move data between the client and the server without making the user wait. Perhaps the most common application of this is prefetching, in which an application anticipates a future need for certain data, and downloads it to the client before the user requests it, thereby speeding up a subsequent response. Google Maps uses this technique to move adjacent map segments to the client before the user scrolls their view.
  • Network efficiency. The network traffic may also be significantly reduced because an application-specific client engine can be more intelligent than a standard Web browser when deciding what data needs to be exchanged with servers. This can speed up individual requests or responses because less data is being transferred for each interaction, and overall network load is reduced. However, use of asynchronous prefetching techniques can neutralize or even reverse this potential benefit. Because the code cannot anticipate exactly what every user will do next, it is common for such techniques to download extra data, not all of which is actually needed, to many or all clients.

[edit] Shortcomings and restrictions

Shortcomings and restrictions associated with RIAs are:

  • Sandbox. Because RIAs run within a sandbox, they have restricted access to system resources. When access to expected/assumed resources is disabled RIAs may fail to operate correctly.
  • Disabled scripting. JavaScript or another scripting language is often required. If the user has disabled active scripting in their browser, the RIA will not function properly, if at all.
  • Client processing speed. To achieve platform independence, some RIAs use client-side scripts written in interpreted languages such as JavaScript, with a consequential loss of performance. This is not an issue with compiled client languages such as Java, where performance is comparable to that of traditional compiled languages, or with Flash movies, in which the bulk of the operations are performed by the native code of the Flash player.
  • Script download time. Although it does not have to be installed, the additional client-side intelligence (or client engine) of RIA applications needs to be delivered by the server to the client. While much of this is usually automatically cached it needs to be transferred at least once. Depending on the size and type of delivery, script download time may be unpleasantly long. RIA developers can lessen the impact of this delay by compressing the scripts, and by staging their delivery over multiple pages of an application.
  • Loss of integrity. If the application-base is X/HTML, conflicts arise between the goal of an application (which naturally wants to be in control of its presentation and behaviour) and the goals of X/HTML (which naturally wants to give away control). The DOM interface for X/HTML makes it possible to create RIAs, but by doing so makes it impossible to guarantee correct function. Because an RIA client can modify the RIA's basic structure and override presentation and behaviour, it can cause an irrecoverable client failure or crash. Eventually, this problem could be solved by new client-side mechanisms that granted an RIA client more limited permission to modify only those resources within the scope of its application. (Standard software running natively does not have this problem because by definition a program automatically possesses all rights to all its allocated resources).

[edit] Management complications

The advent of RIA technologies has introduced considerable additional complexity into Web applications. Traditional Web applications built using only standard HTML, having a relatively simple software architecture and being constructed using a limited set of development options, are relatively easy to design and manage. For the person or organization using RIA technology to deliver a Web application, their additional complexity makes them harder to design, test, measure, and support.

Use of RIA technology poses several new Service Level Management ("SLM") challenges, not all of which are completely solved today. SLM concerns are not always the focus of application developers, and are rarely if ever perceived by application users, but they are vital to the successful delivery of an online application. Aspects of the RIA architecture that complicate management processes are:

  • Greater complexity makes development harder. The ability to move code to the client gives application designers and developers far more creative freedom. But this in turn makes development harder, increases the likelihood of defects (bugs) being introduced, and complicates software testing activities. These complications lengthen the software development process, regardless of the particular methodology or process being employed. Some of these issues may be mitigated through the use of a Web application framework to standardize aspects of RIA design and development. However, introducing greater complexity into a software solution will always complicate and lengthen the testing process, because of the greater number of use cases to be tested. And incomplete testing lowers the application's quality and its reliability during use.
  • RIA architecture breaks the Web page paradigm. Traditional Web applications can be viewed as a series of Web pages, each of which requires a distinct download, initiated by an HTTP GET request. This model has been characterized as the Web page paradigm. RIAs invalidate this model, introducing additional asynchronous server communications to support a more responsive user interface. In RIAs, the time to complete a page download may no longer correspond to something a user perceives as important, because (for example) the client engine may be prefetching some of the downloaded content for future use. New measurement techniques must be devised for RIAs, to permit reporting of response time quantities that reflect the user's experience. In the absence of standard tools that do this, RIA developers must instrument their application code to produce the measurement data needed for SLM.
  • Asynchronous communication makes it harder to isolate performance problems. Paradoxically, actions taken to enhance application responsiveness also make it harder to measure, understand, report on, and manage responsiveness. Some RIAs do not issue any further HTTP GET requests from the browser after their first page, using asynchronous requests from the client engine to initiate all subsequent downloads. The RIA client engine may be programmed to continually download new content and refresh the display, or (in applications using the Comet approach) a server-side engine can keep pushing new content to the browser over a connection that never closes. In these cases, the concept of a "page download" is no longer applicable. These complications make it harder to measure and subdivide application response times, a fundamental requirement for problem isolation and service level management. Tools designed to measure traditional Web applications may -- depending on the details of the application and the tool -- report such applications either as a single Web page per HTTP request, or as an unrelated collection of server activities. Neither conclusion reflects what is really happening at the application level.
  • The client engine makes it harder to measure response time. For traditional Web applications, measurement software can reside either on the client machine or on a machine that is close to the server, provided that it can observe the flow of network traffic at the TCP and HTTP levels. Because these protocols are synchronous and predictable, a packet sniffer can read and interpret packet-level data, and infer the user’s experience of response time by tracking HTTP messages and the times of underlying TCP packets and acknowledgements. But the RIA architecture reduces the power of the packet sniffing approach, because the client engine breaks the communication between user and server into two separate cycles operating asynchronously -- a foreground (user-to-engine) cycle, and a background (engine-to-server) cycle. Both cycles are important, because neither stands alone; it is their relationship that defines application behavior. But that relationship depends only on the application design, which cannot (in general) be inferred by a measurement tool, especially one that can observe only one of the two cycles. Therefore the most complete RIA measurements can only be obtained using tools that reside on the client and observe both cycles.

These issues are discussed in more detail in the paper Rich Internet Applications: Design, Measurement, and Management Challenges.

[edit] The current status of RIA development and adoption

RIAs are still in the early stages of development and user adoption. There are a number of restrictions and requirements that remain:

  • Browser adoption: Many RIAs require modern web browsers in order to run. Advanced JavaScript engines must be present in the browser as RIAs use techniques such as XMLHTTPRequest for client-server communication, and DOM Scripting and advanced CSS techniques to enable the rich user interface.
  • Web standards: Differences between web browsers can make it difficult to write an RIA that will run across all major browsers. The consistency of the Java platform, particularly after Java 1.1, makes this task much simpler for RIAs written as Java applets.
  • Development tools: Some Ajax Frameworks and products like Adobe Flex provide an integrated environment in which to build RIA and B2B web applications.
  • Accessibility concerns: Additional interactivity may require technical approaches that limit applications' accessibility.
  • User adoption: Users expecting standard web applications may find that some accepted browser functionality (such as the "Back" button) may have somewhat different or even undesired behaviour.

[edit] Justifications

Although developing applications to run in a web browser is a much more limiting, difficult, and intricate a process than developing a regular desktop application, the efforts are often justified because:

  • installation is not required -- updating and distributing the application is an instant, automatically handled process
  • users can use the application from any computer with an internet connection, and usually regardless of what operating system that computer is running
  • web-based applications are generally less prone to viral infection than running an actual executable
  • as web usage increases, computer users are becoming less willing to go to the trouble of installing new software if a browser-based alternative is available

This last point is often true even if this alternative is slower or not as feature-rich. A good example of this phenomenon is webmail.

[edit] Methods and techniques

[edit] JavaScript

The first major client side language and technology available with the ability to run code and installed on a majority of web clients was JavaScript. Although its uses were relatively limited at first, combined with layers and other developments in DHTML it has become possible to piece together an RIA system without the use of a unified client-side solution. Ajax is a new term coined to refer to this combination of techniques and has recently been used most prominently by Google for projects such as Gmail and Google Maps. However, creating a large application in this framework is very difficult, as many different technologies must interact to make it work, and browser compatibility requires a lot of effort. In order to make the process easier, several AJAX Frameworks have been developed.

The "rich" in "rich Internet applications" may also suffer from an all-JavaScript approach, because you are still bound by the media types predictably supported by the world's various deployed browsers -- video will display in different ways in different browsers with an all-JavaScript approach, audio support will be unpredictable, realtime communications, whiteboarding, outbound webcams, opacity compositing, socket support, all of these are implemented in different ways in different browsers, so all-JavaScript approaches tend to cluster their "richness" around text refreshes and image refreshes.

[edit] Adobe Flash Player

Adobe Systems is one vendor in this area. Their Shockwave browser extension, and later their Flash Player, have provided browsers with text-refresh abilities since the mid-1990s, and Adobe (then Macromedia) invented the term "rich Internet applications" in 2002.

Adobe Flash technology includes Flash Media Server, Flash Remoting, Central, Connect (formerly Breeze), and Flex, all of which are rendered in viewers' differing browsers via Adobe Flash Player. Adobe points to research carried out by NPD Online which shows that 98% of Internet users have some version of the Flash plug-in, and major services such as Google Video, Hollywood, YouTube and automakers all use these abilities as a matter of course. The Flash Player is supported by many browsers (including Internet Explorer, Mozilla Firefox and Opera), and is distributed as a free browser plug-in. The Player runs across various versions of the Microsoft Windows, Mac OS, and GNU/Linux* operating systems, on set-top boxes and mobile phones, on ambient signage and automobile consoles. The Flash Player is essentially a widely-supported virtual machine that executes byte-code found in files following the SWF format.

[edit] Adobe Flex

More recently, Adobe (previously Macromedia) created Adobe Flex providing a structured programming model and associated data services to create RIAs. Flex uses MXML to declaratively define the application user interface elements and uses ActionScript for client logic and procedural control. Both are compiled into a SWF file where they run in the Flash Player.

[edit] Windows Presentation Foundation

With the .NET 3.0 Framework, Microsoft introduced Windows Presentation Foundation (WPF) which provides a way to build Rich Internet Applications using XAML and languages like C# and Visual Basic. In addition, Microsoft has announced Windows Presentation Foundation/Everywhere which will provide a subset of WPF functionality on devices and other platforms.

[edit] ActiveX Controls

Embedding ActiveX controls into HTML is a very powerful way to develop rich Internet applications, however they are only guaranteed to run properly in Internet Explorer. At the time of this writing, the Adobe Flash Player for Internet Explorer is implemented as an ActiveX control for Microsoft environments, as well as in multi-platform Netscape Plugin wrappers for the wider world. Only if corporations have standardized on using Internet Explorer as the primary web browser, is ActiveX per se a good choice for building corporate applications.

[edit] Java applets

Java applets run in standard HTML pages and generally start automatically when their web page is opened with a modern web browser. Java applets have access to the screen (inside an area designated in its page's HTML), speakers, keyboard and mouse of any computer their web page is opened on, as well as access to the Internet, and provide a sophisticated environment capable of real time applications.

[edit] Java applications

[edit] User Interface languages

As an alternative to HTML/XHTML new user interface markup languages can be used in RIAs. For instance, the Mozilla Foundation's XML-based user interface markup language XUL - this could be used in RIAs though it would be restricted to Mozilla-based browsers, since it is not a de facto or de jure standard. The W3Cs Rich Web Clients Activity[1] has initiated a Web Application Formats Working Group whose mission includes the development of such standards [2].

RIA's user interfaces can also become richer through the use of scriptable SVG (though not all browsers support native SVG rendering yet) as well SMIL.

[edit] Other techniques

RIAs could use XForms to enhance their functionality.

Using XML and XSLT along with some XHTML, CSS and JavaScript can also be used to generate richer client side UI components like data tables that can be resorted locally on the client without going back to the server. Mozilla and Internet Explorer browsers both support this.

[edit] RIA with real-time push

Traditionally, web pages have been delivered to the client only when the client requested for it. For every client request, the browser initiates an HTTP connection to the web server, which then returns the data and the connection is closed. The drawback of this approach was that the page displayed was updated only when the user explicitly refreshes the page or moves to a new page. Since transferring entire pages can take a long time, refreshing pages can introduce a long latency.

[edit] Demand for localised usage of RIA

With the increasing adoption and improvement in broadband technologies, remote latency is becoming less of an issue. Furthermore one of the critical reasons for using an RIA is that many developers are looking for a language to serve up desktop applications that is not only desktop OS neutral but also installation and system issue free.

RIA running in the ubiquitous web browser is a potential candidate even when used standalone or over a LAN, with the required webserver functionalities hosted locally.

[edit] Client-side functionalities and development tools for RIA needed

With client-side functionalities like Javascript and DHTML, RIA can operate on top of a range of OS and webserver functionalities.

[edit] References

  1. ^ W3C (March 15). W3C Rich Web Clients. w3c.org.
  2. ^ W3C (March 15). Web Application Formats Working Group. w3c.org.

[edit] See also

[edit] External links

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