Chapter 15 598 The High-Level System View Travel Agent Office Headquarters VacationApplet HTTP GET XML Document VacationServlet com.wrox.pjxml Package DealsFinder DealsParser Lightweight Aelfred Parser DOMBuild DOMWriter Apache Xerces Parser queryBean sqlBean JDBC Database Access Travel Deal(s) In more detail, the figure above shows all the components of the system – including their class names. The following sections include the description of the client and server classes and what they do in the system. Note that we use an HTTP GET transaction for information exchange between the client and server. This is necessary in order for the application to work through the firewalls installed at the headquarters and at many of the travel agencies. The Sell-offs XML Document for Data Exchange The XML document being transferred from the server to the applet on the client is a list of sell-offs. Here is what an instance of the document may look like: <?xml version="1.0" encoding="UTF-8"?> <selloff>   <trip number="31" region="2">     <startdate>April 15</startdate>     <duration>1 week</duration>     <location>Moon Palace in Cancun</location>     <price commission="400">1899</price>   </trip>   <trip number="32" region="1">     <startdate>June 19</startdate>     <duration>2 weeks</duration>     <location>Princeville Hotel in Kauai</location>     <price commission="700">2699</price>   </trip>