Device Detection
and Capabilities
We
looked at what WALL can do and how easy it is to implement it. But
how does it do that? WALL, and many other open-source (and
commercial) tools use WURFL—Wireless Universal Resource File.
The mDevInf tool that we saw earlier in this chapter is entirely
based on WURFL. WURFL is a massive XML file, listing capabilities of
all known mobile devices (almost!). It is actively maintained and
also derives information from UAProf—another standard for
managing device capabilities.
At
the heart of any device detection is the User Agent header sent by
the browser. All device detection techniques check the User Agent
($_SERVER['HTTP_USER_AGENT'] variable for PHP) and look up their
database to find the characteristics of that device.
Here
are some of the things WURFL can tell you about a device:
Screen
size of the device
Supported
image, audio, video, ringtone, wallpaper, and screensaver formats
Whether
the device supports Unicode
Is
it a wireless device? What markup does it support?
What
XHTML MP/WML/cHTML features does it support? Does it work with
tables? Can it work with standard HTML?
Does
it have a pointing device? Can it use CSS?
Does
it have Flash Lite/J2ME support? What features?
Can
images be used as links on this device? Can it display image and
text on the same line?
If
this is an iMode phone, what region is it from? Japan? US? Europe?
Does
the device auto-expand a select drop down? Does it have inline input
for text fields?
What
SMS/MMS features are supported?
The
list goes on. But you can make some intelligent decisions in your
application based on the device now. You can even conditionally print
<wall> tags. E.g. show a download link only if the device has
download support.
WURFL
API is available in many programming languages, including Java, PHP,
.Net, Ruby, and Python. You can download it from:
http://wurfl.sourceforge.net/.
XML Processing can
Bog Down My Server, is There Something Easier?
Yes!
The WURFL XML file is above 4MB, and despite many structural
optimizations, processing it on every request will certainly slow
down your server. Many APIs provide caching to speed things up. But
having this available in a database will be best. Tera-WURFL is a PHP
package that uses MySQL to store WURFL data. It bundles WALL and an
admin panel—making it the top choice for mobile web adaptation.
Setting
up Tera WURFL involves downloading the latest package from
http://www.tera-wurfl.com/, extracting the files and entering the
database connection information in the configuration file. It will
load up the device data to the database and can start serving WALL
pages.
What
About W3C's DIAL?
W3C's
DIAL (Device Independent Authoring Language) is a combination of
XHTML 2, XForms, and DISelect. DIAL (http://www.w3.org/TR/dial/) was
created to develop a language that will allow consistent delivery
across devices and contexts. Though the language is new, it's getting
a good response and is something to keep track of!
|
Feedback Form (ExpandCollapse)
|
|
