Mobile devices face several constraints compared to personal computers. These constraints include
Mobile device manufacturers, therefore, considered it neither practical ”nor particularly useful, in most cases ”to implement a full version of HTML. Many of the features, such as frames and tables, are not viewable on the small screens of most mobile devices, so markup languages were developed that were limited to the capabilities of most mobile devices.
Four different types of markup are currently being used on different devices. The following sections offer brief descriptions of what they are.
Wireless Markup Language (WML) is part of the Wireless Application Protocol (WAP) specification. This is the de facto worldwide wireless standard that is used by mobile devices in most countries . WML is an XML-based markup language designed to make the most of small mobile devices. WML specifications can be found at http://www.wapforum.org. Currently, WAP devices are used primarily by businesses, and available content is geared toward this. As more and more people have devices that use this standard, content for them will become more consumer-orientated.
Designed by a consortium of Japanese electronics manufactures, Compact HTML (cHTML) is a subset of HTML 2.0. Therefore, it is easy for developers to use, and cHTML Web sites can be viewed on any normal Web browser in addition to mobile devices. The cHTML standard can be found at http://www.w3.org/TR/1998/NOTE-compactHTML-19980209/.
Used primarily by Japan's NTT subsidiary DoCoMo in their iMode-enabled cell phones, cHTML might be thought of as a waste of time by many developers, except that more then half of the total world users of mobile devices use cHTML-based iMode. Currently, more than 80% of worldwide mobile device users are in Japan, with about 70% of them subscribing to NTT DoCoMo's iMode service. There are more than 28 million users of the iMode service in Japan. Additionally, NTT DoCoMo has partnered with AT&T with the idea of introducing iMode to the United States. The large numbers of current users make iMode an attractive market for which to develop applications.
Primarily used by consumers, iMode has a large number of sites for a variety of services, including banking, shopping, and restaurant guides.
Although most mobile devices are too limited in capability to display HTML, devices such as hand-held computers and organizers do have this capability. Screen size is still an issue, and developers will still need to design special versions of their sites that cater to the capability of these devices. Also, newer versions of cell phones, such as those from Sanyo and Nokia, are capable or rendering WML, cHTML, or HTML.
This is really the future of mobile markup languages. Although currently implemented on only a limited number of devices, just about all the mobile device manufacturers and service providers, including NTT DoCoMo, have committed to moving toward this standard. XHTML Basic is a simplified version of XHTML, which is the XML-based version of HTML. Specifications for XHTML Basic can be found at http://www.w3.org/TR/xhtml-basic/.