B2B Integration : A Practical Guide to Collaborative E-commerce

Wireless Technologies 351
a somewhat limited development environment, particularly for more
media-rich devices such as Microsoft's PocketPC and Palms IIIc.
12.3.2. Wireless Markup Language (WML)
Phone.com's HDML (Handheld Device Markup Language) served as
the basis for Wireless Markup Language (WML). WML is a descendant
of Standardized General Markup Language (SGML) and XML. It is
optimized for low bandwidth and is specified by the WAP Forum.
WML looks a lot like Hypertext Markup Language (HTML), but uses a
deck and card metaphor. It contains variables that can be used in all
cards in the same deck.
WML differentiates from HTML in the following ways: it is case
sensitive, the standalone tags end with a '/', form tags are not needed
and select lists do not look the same. Tables are not as dynamic as with
HTML and WML has strong semantics: no errors are allowed. The
parts of a WML 'page' consist of a deck and one or more cards. The
top-most card is the first to be displayed. An action can be taken in
response to other events, such as timer timeouts. A card can also set
variables that can be used by other cards or WMLScripts. Variables set
in one card can be used in others, as long as the memory is not erased.
WML building blocks are cards (e.g., ), paragraph items
(e.g., , ) text formatting (e.g., , ), tables and
images (e.g., ), select and anchor (e.g., ), input field and set variables (e.g., ), triggers (e.g., ).
Since WAP applications are XML-based programs, they must start
out with a valid XML prologue containing the XML version and a
pointer to the XML definition of the language being used. Examples of
code follow: