UML Weekend Crash Course™ - To Parent Directory

294
Sunday Afternoon
MVC pattern in the case study
The case study requirements specify that users must be able to query their appointments
and contacts from both traditional wired Web clients and wireless Web clients such as cell
phones. For the wired Web clients, customers will access the system via Web browsers such
as Internet Explorer or Netscape Navigator and the system will generate HTML for those Web
browsers to display.
Wireless devices such as cell phones usually have extremely limited display capabilities,
very limited input devices such as keypads, limited network bandwidth, and unreliable network
availability. As a result of these limitations, they have their own browsers, protocol,
and markup languages for their special requirements. In North America, most wireless Web
clients have a micro Web browser that communicates via the WAP protocol and interprets
Wireless Markup Language (WML). WML looks very similar to HTML, but it is more compact
and more limited to meet the needs of the restricted wireless devices. Because most of the
case study wireless users have devices that use WML, the architects decide to use that for
the wireless interface.
The system requires two views for interfaces to the querying parts of the application: an
HTML view for traditional wired Web clients and a WML view for wireless Web clients. In
addition, the layout and flow of those views are different because wireless Web clients must
be carefully designed to be easily usable on limited devices. On the other hand, the fundamental
business logic and data business services are the same for both interfaces. The Model
View Controller design pattern principles make this a very simple problem to resolve.
Because your JSPs are the view of the system, there are two sets of JSPs: one with HTML
content, and one with WML content. Both sets of JSPs talk to the same JavaBeans for the
business logic and data manipulation. This is shown in the UML Component diagram in
Figure 28-5.
Traditional
Wired Web
Browser
Model
JavaBeans
Wireless Web
Browser
View
JSP pages
with WML
content
JSP pages
with HTML
content
Figure 28-5 UML Component diagram, two views with MVC design
The next thing to consider is whether the system requires any special software or hardware
configuration to communicate with the wireless Web clients. Wireless Web clients communicate
using the WAP protocol instead of the HTTP protocol. Because traditional Web
servers are designed to communicate using the HTTP protocol, you might reasonably think
that the system would need another Web server that uses a WAP protocol. In fact, it can
still use a regular HTTP Web server. The wireless network providers have systems called WAP