Page 49 - DCAP512_WAP_AND_WML

Unit 4: Introduction to WML

Notes
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Caution One has to play off the benefits of having many cards on the WAP-enabled device at
once against the time for a very large deck to travel from content server to mobile devices.

Since WML is an application of XML, it has to start with a document prolog. The prolog
states that the particular WML belongs to which version of XML and the gives the location
of the document type definition against which this document will be validated. The document
type declaration tells that the root element in a WML document will be . There will be only
one deck per document. The element defines a WML deck and there will be beginning and
ending tags for each deck. There should be at least one card per deck. A deck also can contain
elements and elements. The paragraph element <p> is being used to mark data in WML for
output.

As it is a wireless network, the data transfer size has to be very minimum. Towards this, WML
documents from the content server have to be compiled into smaller binary file. This process of
compilation is being accomplished by the intermediate WAP Gateway. The compiled binary
file is called WAP binary XML (WBXML). The compilation of WML files is mostly a process of
tokenization, in which the names of the tags and elements in the WML files are replaced by
predefined, single-character codes. This technique drastically reduces the size of each WML
document. When the compiled deck reaches the microbrowser, the reverse process has to be
done by the microbrowser to bring the original document in the content server.
White Space is a generic term for characters in a WML code that serve to break it up visually,
but has no meaning as far as WML is concerned. White space represents spaces, tabs, line
breaks, and so on. WML follows the XML rules as far as white space is concerned. The rule
recommends to ignore it before and after an element and to compress all other sequences of
white spaces into a single space between two words. This process reduces the total number
bytes of a WML application. Thus compilation process actually means applying this rule
about white space as it proceeds. The other important feature is that WML supports inserting
comments in the code. They start with the sequence. The comments will not be displayed in
the microbrowsers.

Did u know? What is HDML?
WML (Wireless Markup Language), formerly called HDML (Handheld Devices Markup
Languages), is a language that allows the text portions of Web pages to be presented on
cellular telephones and personal digital assistants (PDAs) via wireless access.

There are two more possibilities to extend a WML file. They are adding more elements to the
existing deck or adding attributes to the elements that already exist. In WML, there are three
attributes that can be used with almost all elements: xml:lang, class and id. The first one is
xml:lang and this attribute is optional. Its value defines the human language of any data that
may be presented to the user, so that user agent can modify its behavior if there is a need for the
displaying purpose.
By specifying a class attribute with the same value in several different elements, these elements
can be made part of the same class. This feature does not make any impact on the microbrowser
or to the users of that WML application. But this feature can be used by some external program
that was asked to process the decks present in the WML application.
The id attribute is used to provide an element with a unique name within a single deck. The id
attribute specifies a name for a card. This feature is necessary if there is more than one card in the

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