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

WML2 is based on WML 1.x and XHTML Mobile Profile, but it won’t be implemented. XHTML Mobile Profile is based on XHTML Basic, and some browsers will render it - mostly. XHTML Basic, 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 create HTML, a language focused on presentation. Later, the vision of a generalized markup language was rekindled, and XML (eXtensible Markup Language) was created as a (mostly) strict subset of SGML.

When Unwired Planet (later Phone.com, currently Openwave) wanted to create internet access over a mobile 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 the Open 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 created WML (Wireless Markup Language) as an XML 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 Compact HTML. 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 in HTML. Few desktop users would find a special type of link to make a voice call to be particularly useful; it is critical on mobile 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.

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

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

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

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

They started with XHTML Basic to accelerate the convergence of wireless and desktop internet development. With this, they got CSS.

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

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

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

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

Nokia immediately created an XHTML Mobile 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 only XHTML Basic. Unfortunately, while these browsers generate very pretty pages, the usability will frequently be worse than the much-berated WAP.