RIA

百科解釋

目錄·發(fā)展歷史
·優(yōu)點(diǎn)
·缺點(diǎn)
·開(kāi)發(fā)現(xiàn)狀
·List of RIA Platforms / Approaches
·RIA Related Topics
·References

發(fā)展歷史

“富互聯(lián)網(wǎng)應(yīng)用系統(tǒng)”一詞源于Macromedia公司在2002年3月發(fā)表的一份白皮書(shū)，盡管如此，該詞在更早的年代中就已包含以下含義：

遠(yuǎn)程腳本（由微軟于1998年左右提出）
X Internet（由Forrester Research于2000年10月提出）
富（網(wǎng)頁(yè)）客戶端
富網(wǎng)絡(luò)應(yīng)用

傳統(tǒng)的網(wǎng)絡(luò)應(yīng)用程序?qū)⑺薪换?yīng)用都集中在基于“瘦”客戶端的C/S架構(gòu)上。在這樣的系統(tǒng)中，所有處理操作均在服務(wù)器端執(zhí)行，客戶端僅僅是用于顯示靜態(tài)的信息內(nèi)容（如HTML）。這種系統(tǒng)最大的缺陷是所有的交互操作都必須經(jīng)由服務(wù)器端進(jìn)行，首先客戶端要將請(qǐng)求數(shù)據(jù)上傳至服務(wù)器端，然后服務(wù)器端作出響應(yīng)并傳回結(jié)果，最后客戶端在重載響應(yīng)信息。而通過(guò)使用在客戶端執(zhí)行指令的客戶端技術(shù)，RIA可以有效的避免延時(shí)，實(shí)現(xiàn)程序與用戶操作的同步。這種差異有點(diǎn)類似于“終端與主機(jī)”或C/S結(jié)構(gòu)與“胖”應(yīng)用系統(tǒng)的差異。
隨著時(shí)間的遷移，互聯(lián)網(wǎng)標(biāo)準(zhǔn)正在逐漸地改變著，從而以適應(yīng)這種新技術(shù)，所以也就很難為富互聯(lián)網(wǎng)應(yīng)用劃定出一個(gè)明確的概念范圍。但是，所有的富互聯(lián)網(wǎng)應(yīng)用都有一個(gè)相同的特征：它們?cè)诳蛻舳伺c服務(wù)器端之間引入了通常被叫做“客戶端引擎”的中間代碼層。這種客戶端引擎通常作為應(yīng)用初始化的一部分被下載，也可能隨著應(yīng)用的運(yùn)行在后續(xù)代碼中作為補(bǔ)丁被下載并補(bǔ)充進(jìn)來(lái)�？蛻舳艘娉洚�(dāng)瀏覽器的一個(gè)擴(kuò)展，而且通常還會(huì)接管呈現(xiàn)用戶界面和與服務(wù)器端進(jìn)行通信的職責(zé)。
富互聯(lián)網(wǎng)應(yīng)用的功能可能會(huì)受客戶端操作系統(tǒng)性能的限制。但是，在大多數(shù)情況下，客戶端引擎會(huì)按設(shè)計(jì)者的意愿執(zhí)行某些編輯好的功能，從而提升用戶界面某些方面或在一定程度上改進(jìn)用戶界面的運(yùn)算速率。而且增加一個(gè)客戶端引擎也不會(huì)導(dǎo)致任何應(yīng)用脫離原有瀏覽器與服務(wù)器端之間的同步交互模式，其實(shí)大多數(shù)富互聯(lián)網(wǎng)應(yīng)用中，客戶端引擎在原基礎(chǔ)上與服務(wù)器端進(jìn)行的是異步通信。

優(yōu)點(diǎn)

缺點(diǎn)

開(kāi)發(fā)現(xiàn)狀

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 Javas cript engines must be present in the browser as RIAs use techniques such as XMLHTTPRequest for client-server communication, and DOM s cripting 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 such as Curl, Adobe Flex and Microsoft Silverlight provide an integrated environment in which to build RIAs.

Accessibility concerns: Additional interactivity may require technical approaches that limit applications&＃39;&＃39;&＃39;&＃39; 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.

List of RIA Platforms / Approaches

RIA Related Topics

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.

Demand for localised usage of RIA
With the increasing adoption and improvement in broadband technologies, fewer users experience poor performance caused by remote latency. 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.

Client-side functionalities and development tools for RIA needed
With client-side functionalities like Javas cript and DHTML, RIA can operate on top of a range of OS and webserver functionalities.

User interface languages
Instead of HTML/XHTML, new user interface markup languages can be used in RIAs. For instance, the Mozilla Foundation&＃39;&＃39;&＃39;&＃39;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 W3C&＃39;&＃39;&＃39;&＃39;s Rich Web Clients Activity[1] has initiated a Web Application Formats Working Group whose mission includes the development of such standards [2]. The original DARPA project at MIT which resulted in the W3C also resulted in the web content language Curl which is now in version 5.0.
RIA&＃39;&＃39;&＃39;&＃39;s user interfaces can also become richer through the use of s criptable scalable vector graphics (though not all browsers can render those natively yet) as well as Synchronized Multimedia Integration Language (SMIL).

Other techniques
RIAs could use XForms to enhance their functionality.
Using XML and XSLT along with some XHTML, CSS and Javas cript 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.
The Omnis Web Client is an ActiveX control or Netscape plug-in which can be embedded into an HTML page providing a rich application interface in the end-user&＃39;&＃39;&＃39;&＃39;s web browser.
Appcelerator is an open source platform for developing rich Internet applications using a service-oriented architecture and standards such as HTML, CSS and Javas cript. Appcelerator applications can integrate automatically with several different integration points on the service tier using Java, PHP, Python, .NET, Perl and Ruby on Rails. Appcelerator applications can use pre-built widgets to assemble high quality RIAs. Appcelerator is licensed under the GNU GPL version 2 License.

References

^ W3C（2008年3月15日）．W3C Rich Web Clients．w3c.org．
^ W3C（2008年3月15日）．Web Application Formats Working Group．w3c.org．

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