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ASP

HDML or WML? By Christina Biggs
By: aspfree
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    2003-01-01

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      So you've heard of HDML and you've heard of WML, but you don't know the differences, and you don't know which to use. Perhaps you're already using one and thinking of switching to the other. Perhaps you've heard that they are the same (as I first did). Let's clear up some of this confusion. First, some back ...

     


    So you've heard of HDML and you've heard of WML, but you don't know the differences, and you don't know which to use. Perhaps you're already using one and thinking of switching to the other. Perhaps you've heard that they are the same (as I first did). Let's clear up some of this confusion.

    First, some background information. In May of 1997 Unwired Planet, a member of the World Wide Web Consortium (W3C), submitted a request to the W3C for the HDML (Handheld Device Markup Language) Specification. The full specification can be found at www.w3.org. Although the submission was acknowledged by the W3C, it is still considered a "working draft" and no further enhancements have been made since its inception. In June of 1999 the WAP Forum, currently enrolling over 200 members, released WML (Wireless Markup Language) v1.1 and shortly after, it released v1.2 in November of 1999. The most recent WML Specification can be found at www.wapforum.org.

    Both languages share the same basic programming model and functionality; however, there are some notable differences to discuss. The main difference is that WML is XML-based, while HDML is not. The main benefit of being XML-based is that a company can use commercially available XML tools to generate, parse and manipulate WML, and they can also user XSL/XSLT to construct WML decks from XML meta-languages.

    Another major difference between HDML and WML is that HDML does not allow scripting, (sorry JavaScripters), while WML allows it's own version of JavaScript, called none other than WMLScript. WMLScript allows the programmer to check the validity of user input, access other facilities on the device (make a call on a phone, add a number to the phone book, etc.), generate messages and dialogs, and other device-specific tasks. HDML has the functionality to do most of the same tasks; however, using WMLScript reduces overall network traffic by performing the task locally.

    HDML does not have a DTD (Document Type Definition) while WML does. As expected, there are also other smaller functionality and syntax differences such as WML's intrinsic events and the ways in which variables are set and passed.

    Feature

    HDML

    WML

    XML-based

    No

    Yes

    DTD available

    No

    Yes

    Scripting

    None

    WMLScript

    Display Cards

    Yes

    Yes

    Choice/Select Cards

    Yes

    Yes

    Entry/Input Cards

    Yes

    Yes

    Nodisplay Cards

    Yes

    Yes

    Images in Text and Anchors

    Yes

    Yes

    Variables

    Yes

    Yes

    Deck Access Control

    Yes

    Yes

    Deck Cache Control

    Yes

    Yes

    Timers

    No

    Yes

    Multiple Choice Lists

    No

    Yes

    Bookmarks

    Yes

    No*

    Nested Activities

    Yes

    No**

    Images in Labels and Choices

    Yes

    No**

    Mobile Originated Pre-fetch

    Yes

    No**

    Key Accelerators for Links

    Yes

    No**




        * UP.Browser supports this feature via WML meta tag
        ** Supported by Up.Browser 4.0 via Phone.com WML extended tag

    So which language is the most promising pick for the future? Based on the aforementioned facts, I'd have to say that WML is going to live much longer and go farther than HDML. Unfortunately, I think Unwired Planet came out with HDML just a tad before its time. When the HDML Spec was released, XML was so new, Unwired Planet did not know enough about it to make HDML based upon it. Although the Phone.com's UP.Link platform will continue to support applications written in HDML, they are recommending to its users to move to WML. Remembering this and all the other limitations of HDML, I think WML, or some form thereof, will stick around to see the future of WAP.

    In Europe and Japan, some WAP devices already do not accept the HDML format. In the US and Canada many of the commercially available CDMA and CDPD phones only support HDML. It is most likely that the future US and Canadian phones will all support WML also. Fortunately, it is not difficult to convert HDML to WML and the learning curve should be minimal.


    References:

    W3Schools.com
    WAP Forum
    W3C Submissions
    Phone.com


    DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware.

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