Java and XML

Push Versus Pull

So far, we have looked at building our applications assuming that the application clients would always pull data and content. In other words, a user had to type a URL into their browser (in the case of the mytechhbooks.com new book listings), or an application like the mytechbooks.com servlet had to make an HTTP request for XML data (in the case of the Foobar Public Library). While this is not a problem, it is not always the best way for a company like mytechbooks.com to sell books. Clients pulling data have to remember to visit sites they would buy items from, and often don’t revisit those sites for days, weeks, or even months. While those clients may often purchase goods and services when they do remember, on average, those purchases do not result in as much revenue as if small purchases were made more frequently.

Realizing this trend, mytechbooks.com wants to be able to push data to its clients. Pushing data involves letting the client know (without any client action) that new items are available, or that specials are being run. This in turn allows the client to make more frequent purchases without having to remember to visit a web page. However, pushing data to clients is difficult in a web medium, as the Internet does not behave as a thick client: it is harder to send pop-up messages or generate alerts for users. What mytechbooks.com has discovered, though, is the popularity of personalized “start pages” like Netscape’s My Netscape and Yahoo’s My Yahoo pages. ...