Wireless Apps: The Reality Today

Introduction
Today's Wireless environments
Multi-Device Wireless environments
Purpose of a Wireless application

Multi-Device Wireless environments

Introduction

Web applications based on application servers offering multi-device support are tending to replace scripting languages. Although they require greater modeling work during the early phases of application development, these solutions have the advantage of being based on a single data layer. The separation of data and presentation is now the objective of these application layers. The tendency is therefore to use the new document description standards (such as XML) to achieve this. These application servers are Java-based, on the whole.

Architecture

Setting up Wireless applications is now more complex than setting up conventional Web applications.

The main difficulty can be put down to the fact that content needs to be provided for an ever-increasing number of devices. Hence, the language, protocol and interface must all be taken into account when setting up the service. The ideal development environment should therefore clearly separate content from presentation. Indeed, such an environment would mean we would not have to worry about the specific features of each device, while remembering nonetheless that these exist!

A multi-device environment must therefore be independent from:

• The access platform: The client side of the application must be easy to implement.
• The network and protocol: The system must be able to communicate with as many Wireless networks as possible.

The extensibility of the system is also important, as it must allow support for devices which do not yet exist.

Technical Multi-Device Architecture

An example of a multi-device application

Our next step will be to create a multi-device application using XML/XSL. Derived from XML meta-language, XSL is a language in its own right. Its elements and attributes are described using XML syntax. Both XSL and XSLT are W3C specifications; version 1.0 has been an official recommendation since November 16, 1999. XSLT describes the manner in which an XML document can be transformed into another XML document. An XSLT Processor is needed to carry out an XSL transformation. The processor takes an XML document and an XSL stylesheet and generates output (XML, HTML, WML…). We used the Xalan processor for the XSLT example presented in this article.

XSLT Architecture

Our XML Document:

Our HTML XSL stylesheet:

Our WML XSL stylesheet:

From this example, we generate HTML content on the fly using a Java Servlet. Alternatively, we could have used another stylesheet to generate WML or HDML content — all you need is to have as many stylesheets as desired presentations. True, application servers offer more and more components for reading/writing XML flow, but what are really lacking are more highly developed components capable of exploiting XSLT fully and easily.

Recap

From this short example we can see that it is possible to use a single data layer (the XML document in our example) to build a multi-device Wireless application. But as we saw earlier on, to implement such applications more extensive study is required in initial phases. Not only must you have an application which can be used in Wireless, but you also need to take the particular features of each device into account.

Printer Friendly Version

TechMetrix Research is a technically focused analyst firm focused on e-business application development needs. Based in Boston, Mass., the firm publishes comparison reports and product reviews designed to aid enterprises with decision making and to keep pace with the fast-moving e-business market.

TechMetrix is a U.S.-based subsidiary of SQLI, a European company that offers on-site development services to international organizations. SQLI specializes in e-business project development.