HDML X-Press Course

The Wireless Web in the US

HDML (Handheld Device Markup Language)

Note: This HDML crash-course is just a short introduction of HDML, ccWAP.com is quite certain, that this language will loose its importance very fast and therefore we will not go into this matter more thouroughly. If you have any questions, we will be happy to answer them. Please write to: hdml@ccwap.com

HDML is a programming language developed by Phone.com for wireless web applications and pages. This is still the standard for some cell phones in the US while WML is the world-wide leading standard. Most WML browsers understand HDML, while most HDML browsers can only understand and display parts of WML and no WMLscript. HDML is a language very rarely used outside of the American continent. The only exception to this is Japan, in which HDML is also used sometimes. Still, since i-Mode is the ruling power in that country and HDML is no real threat to the i-Mode technology.

To get a little more insight into HDML, we will compare it to the predominant WML. HDML can actually be called a predecessor of WML, since it was Phone.com's first try to find a unifying programming language for mobile devices. Unfortunately, some American companies were too fast with adapting the new HDML standard, because just a little later, HDML was being outdated with the invention of WML.

Unlike WML, HDML is not based on XML. In addition, HDML doesn't have a Document Type Definition (DTD) like WML, and despite those flaws can HDML do a lot that WML can.

Of course, WML is the superior language to HDML, however there are some issues in which HDML has a slight advantage. Here is a short list of the features included in HDML but not in WML.(March 99)

Bookmarks
Nested Activities
Mobile Originated Pre-fetch
Key Accelerators for Links

The biggest disadvantage of HDML is probably the fact, that WML has a script language (WMLscript), while HDML does not.

Just like with WML, HDML pages are called cards and the entire site is called a deck. The start of each card is the specification tag. The tag for HDML is much shorter than the tag for WML (which notes the XML-sources etc.).

Example HDML specification tag: <HDML VERSION=3.0>

Despite the obvious similarities to HTML, HMDL has many features unknown to HTML-cracks. Two of the most used tags are <Action> and <Display>.

<Display> is the more or less direct counterpart to HTML's <Body> and contains one display card.

Unlike with WML, HDML offers the possibility to directly link keys on a mobile device to an action. This happens with the help of the <Action> tag. Unless the HDML-programmer assigns a function to a key, each key will have a default action.

HDML Example:

<HDML VERSION=3.0>
<DISPLAY NAME=air>
<ACTION TYPE=ACCEPT LABEL=drj TASK=GO DEST=#drj>
M. Jordan Career Stats

<BR>NBA Titles: 6
<BR>MVP's: 5
</DISPLAY>
<DISPLAY NAME=drj>
<ACTION TYPE=ACCEPT LABEL=bir TASK=GO DEST=#bir>
J.Erving Career Stats
<BR>NBA Titles: 1
<BR>MVP's: 1
</DISPLAY>
<DISPLAY NAME=bird>
L.Bird Career Stats
<BR>NBA Titles: 3
<BR>MVP's : 3
</DISPLAY>

</HDML>

The first card in this deck would look like this.

(Simulation)

Tags and Attributes explained:

TYPE attribute specifies which key to use

LABEL: Sets name of key, normally at the bottom of the display.

TASK: Tells the key what to do (GO is the most common task assignment by far)

DEST tells the key where to go (like in HTML the link can be relative or absolute)

Note: If no card is specified as the first one, the browser will automatically show the first card in the deck, in our case "M.Jordan Career Stats".