Webmaster''''s Guide to the Wireless Internet part 11 doc

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A New Markup:
WML
Solutions in this chapter:
■
A Brief History of Wireless Content
■
WML Overview
■
WML Elements
■
Creating WML Content
■
WML Editors, WAP SDKs, and Emulators
 Summary
 Solutions Fast Track
 Frequently Asked Questions
Chapter 3
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74 Chapter 3 • A New Markup: WML
Introduction
Telecommunications technology has arrived at the point where we can now access
information on the Internet through a mobile cellular device.Wireless Markup
Language (WML) is a lightweight markup language specifically created to address
the limitations of wireless devices and the rigors placed on the transmission of con-
tent over the air through cellular networks.This chapter presents an overview of
the core basics necessary to understand the WML markup language. Once you have
the basics under your belt, you can go on to take a concise yet thorough examina-
tion of the various elements that make up the WML language.
With a thorough understanding of the WML language, you will then take a

look at the various approaches you can take to create WML sites that will really
shine.The chapter provides an overview of the many software development kits
(SDKs),WML editors, and emulators that are available to aid you in the construc-
tion of WML sites.
A Brief History of Wireless Content
The wireless transmission of data occurred longer ago than one may think. Our
ancestors were using sound to transmit primitive coded signals between villages
thousands of years ago, transmitting information without any apparent physical
connection between source and receiver; and the pioneering work of inventors
such as Samuel Morse and Charles Babbage in the 19th and 20th century laid the
foundations for the massive worldwide cellular networks we now enjoy.
Similarly, there is more than meets the eye when examining the Wireless
Application Protocol (WAP) and specifically, the WML that WAP specifies,
because WML has its historical roots in the development of several separate
offerings from different vendors.
Developing the Intelligent
Terminal Transfer Protocol
The Intelligent Terminal Transfer Protocol (ITTP) was developed by Ericsson in
1995 with the specific aim of allowing network operators to provide enhanced
wireless services to their subscribers. ITTP essentially handles the communication
between the network-based application and an appropriately equipped mobile
phone, however, its limitation is that such services are specific to the network
implementing them.
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Developing the Handheld
Device Markup Language
The Hypertext Markup Language (HTML) necessitates a clear visual and struc-
tural reference with which to successfully render content within Web browsers.

Much of HTML is unnecessary to users of wireless devices, and with the band-
width overhead present in current cellular networks, developing wireless content
with just HTML doesn’t make sense. Much of the HTML would be unnecessary
or even useless to the end device.This problem was very much in the minds of
Unwired Planet, which in mid-1996 developed the Handheld Device Markup
Language (HDML) and made it available to developers.
HDML is a lightweight language designed to allow specially equipped “thin-
client” wireless devices to access Internet-based content using the underlying
World Wide Web transports and protocols. Unwired Planet submitted their pro-
posal for HDML to the World Wide Web Consortium (W3C) in April 1997.The
specification currently stands at version 3.0 and is used extensively in wireless
devices in the United States.Although the Extensible Markup Language (XML)
had become available around the same time that Unwired Planet submitted
HDML to the W3C, at that time the huge potential of XML had yet to be real-
ized, and it was passed over by Unwired Planet as a means of representing wire-
less content.
Developing the Tagged Text Markup Language
The Tagged Text Markup Language (TTML) was developed by Nokia
Corporation as part of its Smart Messaging solution to solve the same problem
that Unwired Planet was seeking to address with HDML: accessing Internet-
based content from a wireless device.
The Nokia Artus NetGate, (known in the US as the Nokia TTML Gateway)
allowed filtered content to be harvested from existing sites and sent to the user’s
device as a Short Message Service (SMS).The Artus NetGate gateway and an
accompanying NetGate compatible phone (the 8110i for enhanced browsing)
were announced in March 1997.
Forming the WAP Forum
In 1997, the US network operator Omnipoint Communications asked Nokia
and Unwired Planet to apply for the contract to provide wireless content services
to Omnipoint. Omnipoint did not want to have to deal with the proprietary

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76 Chapter 3 • A New Markup: WML
solutions that vendors such as Nokia (with Smart Messaging) and Unwired
Planet (with HDML) proposed and requested that they work together to provide
a single solution. In June 1997, Nokia and Unwired Planet formed the WAP
Forum in response to Omnipoint’s request, also bringing together Motorola and
Ericsson.These initial founders represented over 90 percent of the wireless
market.The aim was to develop a protocol that could be built on any platform to
allow users to interact with services and information as fast and efficiently as pos-
sible.Where HDML dealt with structuring and presenting data to the user,WAP
defines a whole series of specifications that deal with every aspect of Internet-
based wireless communications, including the language used to describe wireless
content.WAP essentially took all that was best from ITTP, HDML, and TTML
and combined them in a single series of protocols (with many improvements
along the way) to form a single network-independent technology that could be
utilized from any appropriately equipped devices.
Combining Languages into
the Wireless Markup Language
The WAP Forum examined the various markup languages being offered by the
different companies and took the best aspects of each to form the Wireless
Markup Language.WML was released by the WAP Forum in 1999 and proved an
immediate success—all the handset manufacturers quickly adopted it.Those
devices that contained HDML browsers also gained the capability to browse
WML content from HDML version 3.1 onwards.
As was noted earlier, when HDML was created, XML was not thought to be
a proven technology. However, with the subsequent runaway success of XML, it
was obvious that WML would serve developers’ needs best if it was formulated as
an application of XML.
At first glance, a WML file looks quite similar to an HTML file.WML uses

brackets (< and >) to enclose elements, and the elements have attributes just as
HTML does. However, this is where the similarity ends.WML is purely con-
cerned with the structuring of data. It does not specify how the elements should
appear on-screen—this is left to the browser, which will render the WML as it
sees fit.This was a deliberate move on the part of the WAP Forum, and though
sometimes criticized for being too unstructured, it has allowed WML to be used
in everything from mobile phones with a tiny two-line display to more sophisti-
cated “Smart Phone” devices such as the Ericsson M280.
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A New Markup: WML • Chapter 3 77
WML offers many improvements over HDML, which this chapter covers
later when it looks at the specifics of the language.The most important change is
that WML, as an application of XML, must abide by the rules that govern the
creation of XML documents.
Projecting Future Growth
As with so many Internet standards and technologies, evolution of wireless stan-
dards continues at incredible speed. Nippon Telegraph and Telephone (NTT)
DoCoMo’s i-mode service, a well documented runaway success in Japan, delivers
a highly popular service to its subscribers using a subset of the HTML language
called compact HTML (cHTML). Roughly equivalent to HTML 3.2 and
requiring no extra server software over and above that used for hosting Web sites,
developers have been able to supply content without the need to learn complex
new protocols.
With such popularity, it might seem safe to say that WAP’s days could well be
numbered, but this is not so.WAP is a continuously evolving specification and (in
line with the continuing development of HTML) is set to embrace XHTML
Basic and Cascading Style Sheets (CSS), though WML will continue to be sup-
ported. NTT DoCoMo also has indicated it is likely to support XHTML in the
future and will thus fall in line with the WAP Forum in ensuring that future

developments are as interoperable as possible and will provide a firm mutual base
to expand upon.
Commenting on the invention of the telephone in 1876,Western Union said
“This ‘telephone’ has too many shortcomings to be seriously considered as a
means of communication.”Who could have predicted that the humble telephone
would throw off its wire shackles and empower people to receive personal calls
from across the globe?
WML Overview
When HTML was first conceived, it was primarily meant to be a way of struc-
turing data so that its creator,Tim Berners-Lee, could more easily find the con-
tent he needed.As HTML progressed from version to version, the limitations of a
structural markup language became so frustrating that the now near-legendary
Netscape and Microsoft HTML extensions were added, allowing the HTML
authors to specify what sort of fonts were to be used, in what color, and so on.
HTML, together with Cascading Style Sheets (CSS), companion scripting lan-
guages, and a whole plethora of XML-based languages is now a very different
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78 Chapter 3 • A New Markup: WML
beast. However, its development into the mature form it takes today has much to
do with a return to using HTML for what it was meant to do—structure con-
tent. Similarly,WML seeks to provide structure (and therefore meaning) to con-
tent.As mentioned earlier, the use of tags and attributes shows a similarity with
HTML, but this is a language that was developed from the ground up for use on
wireless devices, an environment which has many limitations concerning what
content can be easily viewed.WML has no corresponding CSS style sheet to tell
a device how the content should be formatted—that is left up to the device.This
was intentional, because many types of different devices would be making use of
WML, from personal communicators to appliances.The biggest difference
between WML and HTML is that WML is also an application of XML, bringing

new considerations that we examine in the following sections.
The most important issues that affect how you will approach the creation of
WML documents is that WML as an application of XML is a strictly interpreted
language.A document is a WML document if it is both well-formed and valid.
Additionally,WML must meet certain further constraints, which we examine later
in the chapter.
Creating Well-Formed Documents
A WML document contains elements that have a start element and an end element.If
the element isn’t a container for data, then the element must be self-closing.This
may seem somewhat confusing, so let’s take a look at an example partial docu-
ment (don’t worry about what everything means, we take a look at that later).
<wml>
<card>
<p>I like Ice-cream.<br/>Do you?</p>
<card>
</wml>
As you can see, the code has four elements: <wml>, <card>, <p>, and <br>.
The <wml>, <card>, and <p> elements are container elements and as such have
corresponding closing tags.The <br> element, however, is empty—it doesn’t
contain any data, and thus is self-closing, which is indicated by the backslash.
Nesting
WML documents must be well-formed. This intimidating statement simply means
that a document’s elements must match.WML is constructed hierarchically, as
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A New Markup: WML • Chapter 3 79
shown in the example in the preceding section.The opening element that occu-
pies the same position in the hierarchy must correspond to the closing element at
the same level.The following example shows an example of a document that is
not well-formed:

<wml>
<card>
<p>I like Ice-cream.<br/>Do you?<card>
</p>
</wml>
Here, the <card> element has been closed before the <p> element.This is an
example of invalid nesting. In addition to being properly nested, the elements must
be closed, as detailed in the specification. Consider the following example:
<wml>
<card>
<p>I like Ice-cream.<br/>Do you?
<card>
</wml>
The closing element for the <p> element has been left out, which would
result in the document not being well-formed.With the code nested and all
elements closed, we have a well-formed piece of WML:
<wml>
<card>
<p>I like Ice-cream.<br/>Do you?</p>
<card>
</wml>
Nesting of elements should come easily to all those who have been practicing
good HTML. However, due to the very forgiving nature of HTML, a lot of
developers could be in for a big surprise, so it will stand you in good stead to get
into the habit of nesting and closing elements properly, not only in WML but in
HTML as well.
Creating Valid Documents
In addition to being well-formed, a WML document must be valid.Validity is
achieved by the inclusion of a Document Type Definition (DTD).The DTD
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80 Chapter 3 • A New Markup: WML
describes the elements that may legally exist within the WML document and
ensures that for the document to display, the WML document contains only those
elements allowed by the DTD.
To make our previous well-formed example valid we must add the appropriate
XML declaration and the reference to the DTD:
<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "//WAPFORUM//DTD_WML_1.1//EN"
/><wml>
<card>
<p>I like Ice-cream.<br/>Do you?</p>
</card>
</wml>
This example is both well-formed and valid.The following document,
although it is well-formed, is not valid:
<?xml version="1.0"?>
<!DOCTYPE wml PUBLIC "//WAPFORUM//DTD_WML_1.1//EN"
/><wml>
<card>
<para>I like Ice-cream.<br/>Do you?</para>
</card>
</wml>
WARNING
Although the various SDK emulators are excellent for providing in-depth
information on the interactions that take place during the loading and
execution of WML content, the actual end-device will very likely react dif-
ferently upon encountering an error; it will also almost certainly provide
precious little (if any) information on what went wrong. Do not rely 100
percent on emulators to test your content.

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A New Markup: WML • Chapter 3 81
At first glance, everything may look all right, but <para> is an element that is
not defined in the DTD; therefore, the WML is not valid and will cause an error
on any device that tries to display it. Figure 3.1 shows how well-formed and valid
WML displays; Figure 3.2 shows how incorrectly formed WML will generate an
error.
This example was created using the Openwave UP.SDK emulator, which
includes a handy screen that provides more information in the event of an error.
By referring to the information screen we can see exactly where we went wrong.
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Figure 3.1 Well-Formed and Valid WML
Figure 3.2 The SDK Catches an Error
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