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4.1 to 4.3

4.4. Making the web mobile

As stated in the WAP part of the paper, screens of mobile phones and PDA's are significantly smaller than desktop computers. Laptops are another story, because in all that matters it are full computers, and so have no problems with accessing the web except for the connection. The small screens of PDA's and mobile phones have as a consequence that the content of normal web pages can not be accessed straight-away by those devices. This means that there must be special pages suited to these devices, possibly even different pages for PDA's and for mobile phones. There are a number of solutions to do that. Four of those solutions will be discussed below. They use conversion by hand, automatic conversion, and separation of layout and contents.

4.4.1. WAP(WML)

The "easiest" solution is to make separate pages for WAP devices. This is very straightforward, and will most of the time get optimal results. This is caused by the fact that all pages can be optimized for WAP-devices, and that all WAP-only functions such as programmable keys can be used.

This solution has as a drawback that all pages must be made twice, and must be kept synchronous. The synchronization problem for normal web pages (for example for menu's) has been solved by techniques like ASP, PHP, or, less suitable, CGI. ASP and PHP are server scripting techniques that let web servers compose the web pages dynamically. This does allow for changing the page based on the user agent (web browser). CGI is a technique where the webserver starts a separate program and passes through the (HTML) output. This technique is more suitable for web applications than for dynamic pages because it is overkill.

These techniques make it possible to specify the contents of the page in the page itself, and to import the layout from a separate file/ library. If you import layout from a separate file it is also possible to chose between the layouts based on the users preference or screen size.

4.4.2. HTML to WML conversion

It is not always possible to have WML pages everywhere, or users want to look at pages that are not available in WML format. In that case, conversion must be applied. There are a number of approaches to conversion.

The first technique is re-authoring. Re-authoring can be split in two things: removing irrelevant content, splitting relevant content. The removal of irrelevant content involves the removal of the layout from web pages. The necessity of this process is due to the initial design of HTML. HTML was designed at first to be only content. Web-page designers however, started to use structures like tables to make their pages look better. For WAP-devices this layout is too heavy, and should be removed or replaced by simple menus.

Splitting relevant content is the process of splitting one page into several new pages.

Section outlining

An example of this is found in this picture. This technique makes the page a lot smaller without losing content.

Another technique employed is image reduction. Image reduction is very difficult because the decision whether to resize, remove or keep the image must be made looking at the content and role of the image. A way to overgo that is to resize every image and provide a mechanism for the user to view the full-size image if necessary. This can by done by making the picture a link to the original picture. These conversion systems do work, but are still in a development stage. One very important thing is that the huge variety of web pages causes the converters to perform well on some pages better than on others. This means it should be possible to customize the converters according to the web-site involved.

Of course converters cannot fully support every feature of WML, because the involved web-pages do not support it. Another problem is that plug-ins such as flash are not supported at the moment by these converters. We expect the translation of javascript into wml-script will pose some problems, although wml-script is designed to be mostly a subset of javascript. Of course in the most pages javascript is irrelevant and can be left alone, but in some pages it is essential.

4.4.3. HTML to HTML conversion

Besides converting from HTML to WML it is also possible to convert HTML to HTML but adapted to smaller screens. Of course this requires devices with bigger screens, and as such is more applicable to PDA's. This technique is also used for bringing the web to television sets, but we will not cover those, because televisions are not mobile.

The problems associated with converting to WML exist also when converting from HTML to HTML. This conversion is maybe a little easier because the screens of PDA's are bigger than those of mobile phones. The basic issue with this conversion is getting rid of the unnecessary layout elements and resizing images.

4.4.4. XML + XSL

The fourth way of bringing the web to mobile users is the way that is also recommended by the WAP-Forum. This is the use of XML and XSL. These new standards from the WorldWideWeb consortium are made to separate content from layout. The content is provided by an XML document. XSL (eXtensible Style Language) then specifies how the XML document should be translated in the appropriate language such as HTML or WML. It is even possible for users to specify the preferred style. This separation of content and layout makes it possible to use the content for a lot of different devices, while only changing the layout. It is even possible to use the content on devices that didn't exist yet when the content was made. Only a new stylesheet is necessary. One other advantage of stylesheets is that the same stylesheet can be used by multiple pages, so there is less duplication of data, and synchronization problems are history.