Upload components are software products that are designed to be embedded into a web site to add upload functionality to it. Upload components are designed to replace the standard HTML4 upload mechanism. Compared with HTML4, Upload Components have a more user-friendly interface and support a wider range of features.
The HTML4 standard supports requesting data to be requested from a client computer and uploaded to a server. The standard mechanism for this type of data transmission is HTML forms.[1][2] With HTML forms a user's files can be uploaded by employing <input/> tag with different attributes. This method allows web site developers to implement basic upload functionality. However, it has the following disadvantages:
Upload components allow for bypassing the HTML upload restrictions and disadvantages noted previously. An upload component is a plug-in which allows uploading files from a client to a server. Usually upload components are developed by third party companies and can be integrated with any website on any platform. The user's Web browser will display the embedded upload component as a part of the web page. Upload components can be built with various technologies: Flash, Silverlight, Java, ActiveX, and HTML5.
The W3C community is in the process of developing a HTML5 standard, the full specification of which is expected by 2014.[3] HTML5 is supposed to support multimedia content without any plug-ins or components. For upload functionality, new HTML5 APIs[4] offer a wide variety of new features, including access to the client's file system and dynamic request-generating and processing of images.
The new HTML5 features could be a good basis for implementing upload components with a sophisticated user interface and the ability to upload any amount of data. Unfortunately, at the moment browsers support those features partially and differently, which is a serious obstacle. The situation becomes worse if we remember that large numbers of users still use Windows XP (28%)[5] and obsolete Internet Explorer versions (11%).[6]
Upload components can be developed on the basis of various technologies aimed at extending browser functionality. Depending on the technology and its features, upload components can support more or less functionality, be more or less configurable, and be easier to use.
Microsoft technologies are preferable
Limited support
Java Applets are components running in a web browser. They are developed in the form of Java byte code. The applets are supported by most modern operating systems and browsers. Java applets have high performance similar to native installed software. Java applets are signed with security certificates to become trusted software, which allows automatic redistribution from a web site and installation on client computers.
Upload components can be implemented as Adobe Flash controls. Flash is a framework for running rich-media applications on the Internet. 24% of all web sites use Flash components,[7] and the Flash player is installed on 99% of Internet-enabled PC's.[8] Flash is a cross-platform and a cross-browser technology that allows Flash upload components to work in various browsers, with the exception of mobile platforms.
Another type of upload components is Silverlight which is a Microsoft technology requiring a browser plug-in to be installed. In features it is very similar to Adobe Flash and it is supported by most modern browsers and operating systems. There are versions of Silverlight for Windows and Mac OS X, and there is also a version for Linux called Moonlight. Silverlight is one of the basic technologies used for Windows Phone applications development.
HTML5 is a new HTML standard developed to add multimedia support to HTML. It is supported on Windows, Mac OS X, Linux, iOS, Android, and Windows Phone. Since the format is still under development and some of the features employed for uploading files are still not part of the standard, HTML5 upload components are not common at the moment. Their support is restricted to a subset of browsers.
HTML5 support has been steadily improving. The best coverage of HTML5 features is provided by the latest version of Chrome, Firefox, Safari and Opera. Internet Explorer provides the least support. Internet Explorer 10 has less support than versions of other browsers; however the coverage will be twice as good as Internet Explorer 9.[clarification needed]
iOS 5 has a sufficiently high level of HTML5 support; however, its level of support remains lower than for desktop browsers.
Windows Phone 7.5 "Mango" has slight support for HTML5, which makes it comparable to desktop Internet Explorer 9's lack of support for the standard.
The latest Android 5.0 supports many more HTML5 features than Windows Phone, but less than iOS.
Mobile browsers’ HTML5 support remains a work in progress.[9][10]
Upload components bring additional features and a user experience that cannot be provided by pure HTML4.
Upload components are used for uploading images, so there are components that have additional features for image pre-upload processing.
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