Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

HDML was developed by Unwired Planet (now Phone.com) as a markup language for pocket-sized devices such as cellular phones and two-way pagers that conform to Internet standards and protocols, and that are constrained to a few lines of display, a limited keypad, and little memory. It is a markup language similar to HTML (Hypertext Markup Language) in concept but designed for developing applications and services for cellular devices. It is compatible with all Web servers, uses little memory, makes efficient use of wireless network transmissions, and supports integrated phone features like voice.

Like HTML, HDML uses commands and statements that display information on a phone, provide input options for the user, and specify how the phone responds when the user presses keys. For example, an HDML statement can instruct a phone to display a prompt and allow the user to enter text. The structure of HDML is a deck of cards instead of a Web page. A Web server sends information to mobile users in the form of a single HDML deck with cards that specify a single interaction between the phone and the user. There are cards that display information, cards that prompt for input, and cards that display lists of options for the user to select.

An HDML drawback is that it is proprietary, although open for use. Carriers that support HDML must support browsers and servers from Phone.com. A more recent development is WML (Wireless Markup Language) by the WAP Forum. It is part of the WAP (Wireless Access Protocol) specification. See WAP (Wireless Application Protocol).

Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.
All rights reserved under Pan American and International copyright conventions.