Without an n-tiered architecture, one-off wireless projects can fall into three major traps. The first is the inability to scale. Thomson Financial was just implementing an n-tiered architecture to facilitate Internet data delivery when Scott came on board five years ago. And while he will not reveal all the details of the project, Scott says it cost millions of dollars and took several years to complete.

In the fourth quarter of 2000, Thomson continued its leading-edge information delivery with First Call, a financial information application that lets investors use their wireless devices to tap more than 800 brokerage houses for real-time corporate earnings data from more than 18,000 companies. As a subscription service, it needs to be accessed by as many people as want it - Scott cannot control the number.

A grassroots wireless application built outside the corporate IT infrastructure wouldn't have scaled because it would not support the queuing needed to handle an unlimited number of data requests. Thomson's users must establish a new connection for each transaction; a database that could accept only one transaction at a time would be both time-consuming and frustrating.

The middleware layer in the n-tiered architecture can queue requests for data so that a user can stay connected during the second it takes to process his request. Since the middleware was already in place as part of the n-tiered architecture, the entire First Call application cost only a few hundred thousand dollars, Scott says.

The second trap is supporting a wireless application that works only with a soon-to-be-obsolete device. Gartner estimates that by 2004 wireless devices will outnumber PCs, and Ken Dulaney, Gartner's vice president of mobile computing, says the devices that will be on the market then haven't been invented yet. Accordingly, if a CIO wants his application to last, he must plan for access by multiple devices.

That reality forced Jeff Sutherland, CTO of Massachusetts-based PatientKeeper, a wireless provider for health-care companies, to design a hospital-focused system that would support multiple wireless devices. When doctors visit hospitalised patients, they traditionally record the services rendered on note cards, eventually submitting them to hospital administrators who in turn bill insurance companies. Between lost cards and illegible handwriting, about 10 per cent of billable charges - around $US1 million for a 100-doctor hospital - go uncollected, according to Sutherland.

With PatientKeeper's system, doctors can use wireless devices to record the services rendered and update the billing system in real time. But Sutherland says most doctors already have devices they use for personal information and would rather not be forced to change. He found that an n-tiered architecture was the only way to design a system that would take into account their preferences. PatientKeeper supports front-end application program interfaces (APIs) for PalmOS and WinCE devices. There are more than 3000 standard interfaces on the back end for integration with legacy health-care systems.

The centralised architecture means that the system will last, and Sutherland has harsh words for the alternative. "I view all of these point and departmental applications as throwaways," he says. "I am going to want to deploy really useful applications across the enterprise. And to do that I am going to have to boot out all these point applications with a specific device or a specific data source."

The third potential problem with one-off projects is their inability to process transactions that require data from multiple sources. An n-tiered architecture allows for this kind of interaction. For example, Missouri-based marketing services company Maritz hosts travel services for its corporate customers, and the complex interactions it requires, such as travel booking, won't work without an n-tiered architecture since travel booking also requires several interactions with different databases. Most of today's wireless applications, such as e-mail, are single-transaction based. That model won't translate to Maritz's travel application, which CIO Gil Hoffman says must request an itinerary, give choices, make a reservation and return a confirmation number as well as handle credit card information. This kind of complex transaction, which requires message queuing available only with middleware, is unattainable with one-off wireless projects that limit interactions to one data source. During the past five years, the company has developed an n-tiered architecture to support high-volume, multidatabase transactions, Hoffman says.