by Thomas Erl
Even though restrictions in usability require most wireless applications to consist of a series of fairly simple user-interfaces, giving your staff or clients the ability to access corporate data from anywhere in the world through the use of a cell phone, can be extremely convenient and efficient (if business requirements needing this type of accessibility exist within your enterprise).
The following paper takes a closer look at wireless technology, with a focus on the XML-based WAP (Wireless Application Protocol) framework:
What is a Wireless Application?
A wireless application is designed for use on an Internet-enabled, mobile hand-held device, such as a cellular phone or a Palm Pilot. These devices have built-in mini or micro-browsers capable of accessing Web content over the Internet.
Even though some hand-held devices are capable of rendering HTML content, their limited screen size and graphic capabilities led to the creation of a new generation of specialized mark-up languages, designed specifically for Web content display on hand-held devices.
One of the most popular platforms for hand-held device communications over the Internet is the Wireless Application Protocol (WAP). Part of the WAP framework is the Wireless Markup Language (WML), which is actually an implementation of XML.
How Does it Work?
Here's a step-by-step description of how a wireless application can interact with an existing Web server (see the diagram below):
|1.||Using a portable hand-held device, such as a cell phone, the user fills out a WML form, and submits the information in a request for an ASP script on a Web server.|
|2.||The WAP Gateway intercepts the request and translates it into a standard HTTP Request and forwards it to the Web server.|
|3.||The ASP script receives and processes the request.|
|4.||The ASP script responds with a standard HTTP Response consisting of a WML page.|
|5.||The WML page is received and validated by the WAP Gateway server, and then forwarded to the portable device.|
|6.||The portable device receives the WML page and renders it on its micro-browser display.|
As with other platforms based on XML, the WAP/WML technology-set is still emerging into the mainstream. As of the writing of this paper, WAP/WML is much more established in Europe than in North America, where the competing Handheld Device Markup Language (HDML) standard is still more prominent. However, research revealed that both WML and HDML standards were created by the same organization: Phone.com. As a member of the WAP Forum, Phone.com is openly dedicated to promoting WAP/WML over HDML, in large part due to its XML-compliance. The fact that it has been used successfully in Europe somewhat reduces the risks typically associated with new technologies.
A major issue with any wireless technology is hand-held device support. The WAP Forum consists of a number of major hand-held device manufacturers, and the latest generation of devices released by these manufacturers naturally have WAP/WML support, however many older devices, and devices from other manufacturers do not. Additionally, compatibility issues exist, even among those devices that do promote WAP/WML support. This is reminiscent of the Web browser compatibility issues, where Microsoft's Internet Explorer would not only render standard HTML tags differently from Netscape Navigator, but each browser would also support proprietary extensions to HTML, requiring developers to create two versions of many Web pages, and then programmatically detect which browser was accessing a Web site in order to determine which Web page to respond with.
Even though WAP is establishing itself world-wide, it is by no means yet the de facto standard for global wireless technology. Several organizations are still actively working on competing solutions, most notably, Japan's i-Mode system, which boasts faster Internet access and enhanced navigation capabilities.
Extending your XML enterprise with wireless technology is pretty straight-forward, especially if that technology is already based on the use of XML. The greatest impact to your organization's infrastructure will be the introduction of a new server layer: the WAP gateway. Responsible for translating (encoding and decoding) data sent to and from the hand-held device, this server product can be expensive to own and maintain, which is why many organizations simply host their wireless applications with ASPs that offer gateways. Since your Web server acts as the contact point for the gateway server, your back-end remains fairly unaffected.
The greatest risk lies in the ever-changing levels of industry support for various technologies. This volatile environment could lead to radical shifts in the future, causing current wireless platforms to become obsolete. Investing in wireless extensions these days is only recommended as a tactical measure for solving immediate business problems. Long-term strategies will need to be flexible enough to accommodate upcoming changes and developments in the wireless industry.
Below are some descriptions for commonly used terms relating to the WAP framwork:
Wireless Access Environment (WAE)
The framework for the set of specifications and technologies developed by the Wireless Application Group (WAG). Essentially, the equivalent to DNA in the Microsoft n-tier world.
Wireless Access Protocol (WAP)
A wireless communication protocol based on XML and IP, reportedly supported by manufacturers representing 90% of the existing hand-held devices. WAG (creators of WAP) is working with the W3C to achieve industry-level standardization.
Protocols related to and governed by WAP include:
• Wireless Session Protocol (WSP)
• Wireless Transport Layer Security (WTLS)
• Wireless Transaction Protocol (WTP)
• Wireless Datagram Protocol (WDP)
Wireless Markup Language (WML)
An XML-based presentation language for creating micro user-interfaces, essentially the equivalent to HTML for the PC.
XML Document Navigation Language (XDNL)
A proposed language that allows for the partitioning of XML documents into multiple subsets suitable for display on non-PC user-interfaces, such as hand-held devices. The most common anticipated use of XDNL is to define the presentation structure of Web pages for micro-browsers.
- Inside XML Schemas
- SOAP in a Nutshell
- Transforming Data with XSLT
- Understanding DTDs
- Why SAX is Good for DOM
- What You Should Know about XPath
- An XHTML Primer
- XLink - Inside and Out
- Data Access with XQuery
- XSL versus CSS
- Another Introduction to XML
- Unifying Corporate Data & Documents
- Replacing HTML Documents with XML
- Meta-Enable Your Enterprise
- The XML Data Custodian
- Integrating XML into the Enterprise
- The Wireless Enterprise
Foreword by Grady Booch
With contributions from David Chappell, Jason Hogg, Anish Karmarkar, Mark Little, David Orchard, Satadru Roy, Thomas Rischbeck, Arnaud Simon, Clemens Utschig, Dennis Wisnosky, and others.
Governing Shared Services On-Premise & in the Cloud by Stephen Bennett, Thomas Erl, Clive Gee, Anne Thomas Manes, Robert Schneider, Leo Shuster, Andre Tost, Chris Venable
For more information about these books, visit: www.servicetechbooks.com