Jean-Baptiste Minchelli, Consultant
Today's
Wireless environments
Introduction
Development of a Wireless application does not usually
require any specific procedure. This means that a number of
vendors have been quick to use Wireless to promote their
products, although these possess no specific Wireless feature.
We could mention Allaire, for example, who proudly announced
their products' support for WAP; in fact, all this turns out
to mean is that a few tags have been inserted.
We will
see that by using standard Web technologies, it is quite
possible to set up a Wireless application.
Existing
environments
The
environment is the non-visible part of the application;
essentially, this refers to a resource which governs much of
the development and operation of the application.
The first
Wireless services were grafted onto existing systems which,
naturally, had not been designed to integrate Wireless
technology. Wireless applications therefore often cohabited
with standard Web applications, quite independently; this
usually involved new developments in order to make new
services available.
Environment of early Wireless
applications
An
example of a Wireless application
Below is a
simple example of a WAP application set up in a relatively
conventional Web environment:
- Web
Server: Apache
- Server-side scripting language: PHP
WAP (which
stands for Wireless Application Protocol) is a specification
from the WAP Forum which aims to define how applications
should operate within the Wireless domain. Although a gateway
is essential in the WAP protocol, it is only implemented by
operators. For information, the gateway works as a link
between the Wireless world and the Web (translation of
requests, content coders, and so on). Therefore, only the
elements mentioned above are required to set up a WAP
application.
Server
configuration
The
application server (or the Web server) needs to be configured
in order to deliver WAP content. So you need to tell the
server when it must make it known that the message is a WAP
message. This means specifying the MIME-types (content-type)
specific to WAP. For Apache, you need to edit the httpd.conf
file and add the following:
AddType
text/vnd.wap.wml wml
AddType text/vnd.wap.wmlscript
wmls
AddType application/vnd.wap.wmlc wmlc
AddType
application/vnd.wap.wmlscriptc wmlscAddType
image/vnd.wap.wbmp wbmp |
The server
is now able to supply WAP content. It is only essential to
specify the MIME-types for static pages. Otherwise, these can
be specified dynamically, as we will see later on.
Application development and testing
WAP
currently uses WML (Wireless Markup Language), which is based
on XML, and WMLScript, based on ECMAScript. If we compare it
to a Web application, we could say that WML plays the role of
HTML (document formatting) and WMLScript is like JavaScript
(client-side scripting language).
Below is
an example of WML:
|
<?xml version="1.0"?>
<!DOCTYPE wml
PUBLIC "-//WAPFORUM//DTD WML 1.1//EN"
"http://www.WAPforum.org/DTD/wml_1.1.xml">
<wml>
<card
id="hello">
<p>
<do
type="accept">
<go
href="Hello.wmls#Display('Hello in
WMLS')"/>
</do>
Hello
world!
</p>
</card>
</wml> |
Hello.wml
And now,
here is an example of WMLScript:
|
extern function
Display(msg)
{
Dialogs.alert(MSG);
return;
} |
Hello.wmls
To test
this first Wireless application, place the Hello.wml and
Hello.wmls in the Web server's root folder, and then browse
the page with a WAP simulator such as that offered by Phone.com (now
OpenWave).
YoSpace
Emulator
The above
picture shows the result that you should then obtain. As long
as your server is accessible via Internet, you should be able
to access your application using any WAP phone. All you need
to do is enter the relevant URL to access the
resource.
We will
now put together a dynamic application which generates WAP
content on the fly. We will use PHP to do this. Of course, it
is equally possible to use any other technology to dynamically
generate documents (ASP, JSP…). Below is the source code for
our example:
|
<?
header("Content-Type:
text/vnd.wap.wml");
echo "<?xml
version=\"1.0\"?>";
echo "<!DOCTYPE wml PUBLIC
\"-//WAPFORUM//DTD WML 1.1//EN\"
\"http://www.wapforum.org/DTD/wml_1.1.xml\">";
?>
<wml>
<card
id="hello">
<p>
<?
$word =
"hello";
$word .= " world!";
echo
$word;
?>
</p>
</card>
</wml> |
Hello.php
It is
crucial not to omit the Content-Type information from the
header. It is this information that enables the different
agents in the protocol to correctly process the message
(gateway, browser…). The rest of the code is conventional —
you insert the PHP code inside the WML code. You can therefore
carry out any processes you want (database access, image
generation…).
Recap
|
Pros |
Cons |
- Uses existing structures.
- Swift to implement.
- Application specifically designed for Wireless
devices.
|
- Requires redevelopment of application.
- Extremely costly in terms of development and
maintenance.
|
From this
rudimentary example, we can see that it is possible to build
any Wireless application. But as we have already mentioned,
the present case involves redeveloping applications. And
since, as we know, you need one version for HDML, one for WAP,
another in HTML 3.2 for PDAs, and so on, it is clear that
development and maintenance costs will quickly begin to add
up.
Images
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