Understanding WAP Wireless Applications, Devices, and Services phần 9 pptx

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Figure 10.12 Typical stovepipe solution to multichannel support.

Figure 10.13 A shared business object: multichannel delivery architecture.

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which may or may not be proprietary. Equally important, each of the subchannels has different operational characteristics

(e.g., the back channel of iTV may be permanently open or not), which needs to be taken into consideration when

designing applications.

A similar situation exists with the mobile channel. As we have already seen, we are faced with the prospect of dealing

with SMS and USSD messages, voice or DTMF-based IVRs, SIM toolkit, WAP, PDAs, and laptops. While there is a

good chance that WAP will become the dominant technology for mobile devices, it will be several years before it is

ubiquitous in the installed base of mobile phones. In the meantime, we are faced with a heterogeneous and fairly diverse

environment. It is therefore probable that the mobile commerce provider will have to be content with at least two of the

above technologies.

In this world, with many subchannels to support, it is desirable to eliminate as much as possible the business

functionality from the channel-specific parts of system. In the current model, the generation of the presentation layer

from the underlying business objects is done on a channel-by-channel basis. While this code is not extensive in a thin￾client environment, there is nevertheless duplication and replication of logic. For larger, new developments it will

probably be worthwhile to introduce another tier in the architecture. Figure 10.14 shows a new channel-neutral

presentation layer.

In this case, rather than trying to postprocess the Web interface into other formats, all the channels derive their

presentation layers from a new channel neutral format (CNF). In this model, a single logical process constructs the CNF

for all channels. This is then parsed and rendered for each (sub)channel. In this way the channel-specific code becomes

more stable and does not need to be changed when the application is enhanced or new application features are added. An

increasingly popular approach to this is to use XML for the CNF. This XML-based intermediary presentation definition

has several advantages.

l Web browsers are evolving to be able to render XML directly by using cascading style sheets (CSS) and

extensible stylesheet language (XSL).

l WML is available as an XML document type definition (DTD).

l Parsers and other XML-based tools are now readily available in sev-eral languages (Java, C++, and Visual Basic).

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