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Just as you can do with HTML, you can roll your own or buy an off-the-shelf solution. One approach with off-the-shelf solutions is to take content that might otherwise employ HTML or other client rendering methods but deliver them in WML format. An example of this is a product called Workstyle Server from Wireless Knowledge, in San Diego, a joint venture between Qualcomm and Microsoft (see "Workstyle Server From Wireless Knowledge"). You install this server in your network between your Microsoft Exchange servers and an external network, such as the Internet, that provides a connection to the wireless carrier. The firewalls shown are optional but a good idea, particularly the external one if you employ a connection to the Internet. The Workstyle Server acts as a proxy on behalf of the mobile user, accessing the Exchange server for mail and calendar information and delivering it to the WAP gateway in WML or HDML format. Lotus Development Corp. is developing a comparable capability with its Mobile Services for Domino product. Expect similar features for other enterprise packages, such as Apple Computer's WebObjects, BEA Systems' WebLogic, IBM's WebSphere and PeopleSoft's Mobile eStore.

You also can outsource the mobile-content hosting function to an increasing number of wireless ASPs (application service providers), such as Broadbeam Corp., InfoSpace and OracleMobile. These service providers not only host applications but can also assist you with the integration of your solution.

Roll Your Own

If you're going to develop your own application, you will need to produce WML or HDML code. HDML has capabilities similar to WML's but is controlled by Phone.com. Phone.com created HDML before WAP even existed, and HDML has continued to evolve in parallel with WAP. In the United States, you need to consider both formats, as AT&T Wireless Services, Sprint PCS and Verizon support HDML, but Nextel Communications and VoiceStream Wireless support WAP. Much of the information here on WML also applies to HDML. WML, which is based on XML, specifies the format and presentation of text, hierarchy of pages and links. There is a version of JavaScript, called WMLScript, that allows local logic execution.

What about converting existing HTML? There are conversion tools available but don't expect any magical process. There is no easy way of effectively condensing rich content to a tiny screen. You really need to design the WML content, taking into account the user interface. You can develop new content in XML and then use extensible style sheets to render the content on different platforms.

There are several WML editors, including online editors, available (see Web Links, at left, for information on AnywhereYouGo. com). There are also several emulators you can use. These allow you to interact with WML content using graphical representations of mobile cell phones right on your large-screen monitor. The content can be on your hard drive or on a separate Web server. Companies such as Nokia and Phone. com also offer SDKs for developing HDML/WML content.

<wml>

<card>

<do type="accept">

<go href="#nextcard"/>

</do>

<p>

Press the Accept button for the next screen

</p>

</card>

The do statement associates a means of invoking an action (pressing the Accept button) to an action, namely going to the next screen. The go statement specifies the URL for the action. The

prints the text on the screen. The advantage of WML editors is that, much as in HTML editors, you don't need to worry about exact syntax. And if you want to elevate yourself one level, tools from companies such as AvidWireless are designed to let you specify content at a higher level of abstraction, wherein the tools format the content for the appropriate user device.

These tools free you from keeping up on all the finicky details of each target device.

WAP Shortcomings

WAP and HDML are very effective for the right applications, but the protocols--and particularly their implementations--have some problems.

First, you have to decide whether to develop your format in HDML or WAP or both. And there are many versions of HDML and WAP available, causing further complications. Multiple phones with varying capabilities also complicate the scene. Their numbers of lines of display vary, as do their graphics capabilities. To some extent, WAP automatically handles different screen sizes, but you still have to decide whether to design for the lowest common denominator. Even worse, because of ambiguities in the WAP specification, different vendors have implemented features differently, and the only way to be sure your application runs correctly is to test it with all the target devices of interest. In addition, WAP gateways from different vendors do not behave identically; therefore, because your application works on one carrier's network does not mean it will work on another carrier's network. These interoperability issues have been plaguing the WAP community, and although major interoperability testing programs have been launched, problems persist.

Security is another issue. Because WAP relies on different security protocols on the wireless links and on the wire-line links, information must be decrypted and re-encrypted at the gateway, resulting in a security solution that is not end to end. The WAP Forum intends to fix this in future versions of the specification.

Despite these difficulties, a large number of companies are developing WAP tools, testing services, hosting services, devices and applications. The industry is in a pioneering stage with a rocky road to travel, but WAP is likely to be used in many new applications.

Peter Rysavy is president of Rysavy Research, a consulting firm that helps companies research, develop and deploy communications technologies. Send your comments on this article to him at rysavy@rysavy.com.