LIS 523/5 - Handheld Devices

WML

WML, or Wireless Markup Language, is a language, written in XML, used to specify content and user interface for WAP (Wireless Application Protocol) devices, such as mobile phones. WML is supported by almost every mobile phone browser. It is scalable from two-line text displays up and supports a simple scripting language called WMLScript.

WML pages are accessed in the same way as HTML pages; the server must deliver them with the text/vnd.wap.wml MIME type. In addition, the server should support some or all of the related MIME types

Some hosting services (for example, LFC Hosting) have plans that include WAP support. Otherwise, you should look for a plan that allows custom MIME types.

Whereas HTML uses the "page" metaphor, WML relies on a "deck of cards" metaphor: a typical WML document contains one or more "cards" through which the user can navigate in sequence or via hyperlinks.

The only normal Web browser that can view WML files is Opera, and, even then, Opera makes no provision for self-identifying as a WAP browser to avoid being redirected to an HTML version of a file. In Windows, Netscape Navigator and Firefox may incorrectly try to open WML files with Windows Media Player, even though they are not associated with that program; Internet Explorer simply cannot find a suitable application to use. You can view WML files on a desktop machine with a free viewer such as OpenWave Systems' UP.Simulator.

HDML

HDML, or Handheld Device Markup Language, is a proprietary language of Openwave, and files in this language can be viewed only with Openwave browsers. The client requests a page through Openwave using a protocol called HDTP (Handheld Device Transport Protocol), rather than WAP, which was developed later. Openwave requests the page from the server, and the server delivers it to Openwave, via HTTP. Openwave then transmits the page to the mobile device via HDTP. The server must give the MIME type text/x-hdml to the file.

HTML for Handhelds

Some wireless device browsers, such as the Blackberry Browser, Neomar's WAP Browser for Palm, or the Opera browser used in Sony Ericsson's P800 handset, have limited support for HTML. Format and functionality are not fully preserved. The browser may note on the screen that the document has been converted. Conversion make take place either on the device itself or on a special server.

HTML files designed for handheld use look like other HTML files except that they have to be simpler and they may contain a meta tag such as

<meta NAME="HandheldFriendly" CONTENT="True">

Special rendering options for pages for handheld devices can be specified in a style sheet in an @media handheld{ } block.

Examples of HTML pages designed for handheld use are http://slashdot.org/palm, http://www.hollywood.com/avantgo/, and http://aa.flightlookup.com/omnisky/.

Opera's SSR (small-screen rendering) technology, available in Sony Ericsson's P800 handset, reformats a Web page written in HTML to fit on a smaller screen. You can preview the small-screen display on a Windows computer by pressing Shift-F11 in Opera 7 and above.

A more recent trend is for handheld devices that support full Web browser capabilities; for example, the Nokia 7700 has a 640x320 pixel screen, allowing it to run Opera in something approaching VGA resolution.

Systems for browsing the Web on low-definition television sets present similar considerations to handhelds. For example, in the MSN TV Viewer rendering of the instructor's Web page, text appears larger than normal and table width is reduced to fit the screen.

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Last updated April 23, 2007.
This page maintained by Prof. Tim Craven
E-mail (text/plain only): craven@uwo.ca
Faculty of Information and Media Studies
University of Western Ontario,
London, Ontario
Canada, N6A 5B7