13.4 Wireless Markup Language | IP in Wireless Networks

This section provides a brief overview of the Wireless Markup Language (WML) used in WAP architectures. WML is the official WAP markup language for exchange of content between wireless terminals and the WAP-enabled network. The most important design elements of WML are due to the nature of mobile personal devices with the following characteristics:

Small display screens
Limited computing power
Limited memory resources
Low bandwidth network connections
Limited and simple browsing abilities

While meeting these constraints, WML shares common characteristics with HTML, which is widely used on the Internet; HDML (Handheld Device Markup Language), an earlier markup language; and XML (eXtensible Markup Language). Utilizing features from these different sources, WML is defined with four major functional areas:

Text presentation and layout
Deck/card organization in WML makes all information organized as decks and cards
Intercard navigation and linking is used when navigating between cards and decks
String parameterization and state management are possible in WLM decks.

Naming within WML is implemented with uniform resource locator (URL) to be compatible with WWW naming. The WML character set is derived from the XML document character set. WML also inherits the syntax information from XML. WML content can include scripts, and these scripts can be invoked from WML. The scripting language used here is WMLScript, which is similar to Javascript but optimized for high-latency, low-bandwidth communications.

WMLScript supports most standard programming constructs and it can be compiled on the server to yield a byte code executable format, which is smaller than the text format, so that it is suitable for the radio. WMLScript matches the WAE requirements for a lightweight language that can be easily parsed and interpreted, is easy to program, integrates with WML, and is a well-known language.