What is the difference between XHTML MP, XHTML Basic, WML, i-mode, and HDML?

XHTMLBasic, XHTMLMobile Profile, and WML2

WML2 is based on WML 1.x and XHTMLMobile Profile, but it won’t be implemented. XHTMLMobile Profile is based on XHTMLBasic, and some browsers will render it - mostly.XHTMLBasic, with CSS, will be widely implemented. Here’s how all these technologies are related to each other.

In the beginning (1974), there was SGML (Standard Generalized Markup Language). And it was too complex. However,SGML was simplified - in both function and structure - to createHTML, a language focused on presentation. Later, the vision of a generalized markup language was rekindled, andXML (eXtensible Markup Language) was created as a (mostly) strict subset ofSGML.

The Wireless Path

When Unwired Planet (later Phone.com, currently Openwave) wanted to create internet access over amobile phone, they analyzed factors such as device memory capabilities, wireless network connection and drop times, device display and control characteristics, and transfer speeds. They developed (although some will argue GeoWorks developed) HDML, or Handheld Device Markup Language.

Later, Openwave joined with Nokia and others to found the WAP Forum, now theOpen Mobile Alliance. This group had the goal of creating a common standard for wireless internet access. They largely took the features of HDML (with some exceptions that frustrated the usability community) and createdWML (Wireless Markup Language) as anXML language. This language proceeded from version 1.0 to 1.3, with version 1.1 the apparent most common browser implementation.

On the other side of the world, Japan’s largest wireless carrier, NTT DoCoMo created iMode (Information Mode) as a wireless service, running on their proprietary CompactHTML. This service became extremely popular, in no small part because of good price models and their restraint from marketing iMode as the web, but rather as information.

iMode and WML 1.x have features not found inHTML. Few desktop users would find a special type of link to make a voice call to be particularly useful; it is critical onmobile phones. WML gave users access to commands associated with screens or items on the screen, not just hyperlinks. This allowed the scroll-and-select phones with one or two softkeys a bit more efficiency in how tasks could be accomplished on the phones.

One major problem with WML was the lack of standard rendering implementation. Some browsers rendered select lists as pop-up lists; other browsers rendered them inline (usually with no other components allowed on the screen). The result was that developers had to pick a browser to target and suffer an unacceptable user experience on the others, or double their work to target multiple browsers.

The W3C Path

Meanwhile, the W3C (World Wide Web Consortium) recast HTML 4 into XHTML 1, using syntactical rules fromXML but the feature set (and tag names) ofHTML. They then modularized XHTML into several units.

The W3C selected a set of modules appropriate for access by devices with limited capabilities. These includedBasic Forms, Hypertext, and Basic Tables. They called this set of modules XHTMLBasic.

One key advantage that XHTMLBasic had over the other wireless markup languages was cascading style sheets (CSS) - useful now that phones have graphical displays.

The Convergence, Almost

NTT DoCoMo and the WAP Forum joined forces to create the next standard for wireless internet access. They wanted to combine the features ofWML,XHTMLBasic, and iMode to create a platform that would serve all their users and developers.

They started with XHTMLBasic to accelerate the convergence of wireless and desktop internet development. With this, they gotCSS.

They added in the functions from cHTML and WML that were not in XHTMLBasic (but were in XHTML): acronym, address, br, b, big, hr, i, small, dl, fieldset, optgroup. The resulting language is a superset ofXHTMLBasic, but a subset of XHTML. They called this languageXHTMLMobile Profile.

They then added the features of WML that could not be found inXHTML. These included navigation aids, onenter events, contexts, and other features (both elements and attributes). In true XML fashion, these were placed in anXML namespace and could be used by putting "wml:" in front of the command. The combinedXHTMLMobile Profile plus WML namespace is WML2.

The Open Mobile Alliance, led by Nokia and NTT DoCoMo, determined that theWML namespace was “just for backward compatibility.” Once this decision was made, the one to make theWML namespace optional quickly followed.

The Open Mobile Alliance decided that since theWML features were for backward compatibility, then a device could beWML2 compliant either if it read WML2, or if it read XHTMLMobile Profile pages and WML 1.x decks. There was no need to be able to readWML tags in theXHTML document.

Current State of Affairs

Nokia immediately created an XHTMLMobile Profile browser, with no WML namespace. The Openwave uses the WML namespace, which is to be expected since most of the features date back to HDML.

Most other browsers - such as the Access Compact NetFront 3.0 (successor to the iMode browser) and the Samsung device browsers, support onlyXHTMLBasic. Unfortunately, while these browsers generate very pretty pages, the usability will frequently be worse than the much-beratedWAP.