Page Monitors - Information Trapping: Real-Time Research on the Web - page 44

In the last chapter, we looked at RSS feeds, which are easy-to-read and easy-
to-follow sources of site changes and content updates. I wish I could tell you
that RSS feeds are the only source you'll ever need to use when setting up
information traps, but that wouldn't be true.
Why not? Because many sites still don't provide RSS feeds. Although RSS
has been around for quite some time, it hasn't gained the prominence you
might think it would. Some site operators don't have the time or interest
to integrate another technology into their site. Others provide alternative
ways for site visitors to keep up with their site's content (such as e-mail
alerts) and don't feel the need to ofer RSS feeds. Still others want you to
actually visit their site and see their ads, rather than receive content via RSS
feeds. he list goes on. So in your search for information, you more than
likely will come across pages you want to continually monitor that don't
have RSS feeds. What's an information trapper to do?
Use a page monitor! his chapter discusses the various kinds of page moni-
tors that are available, walks you through how to set one up, and shows you
how to limit the number of insigniicant page updates you receive.
Nuts and Bolts
A page monitor simply watches HTML pages for changes and then reports
them to you. Generally, the monitoring program grabs the page, then returns
to the same page later, grabs a new copy of the page, and then compares the
two. Any new information that's added to the page is reported to you.
At irst, this sounds great. But unfortunately there's a downside: too many
“false positives.” For example, if a page changes its date every day, this date
change may trigger a false positive to the change monitor, and the change
monitor may incorrectly alert you to the new content. If a page has a visi-
tor counter that gets updated, those updates could also trigger an alert or
false positive. Even tiny things that are updated, such as a corrected spelling
error, can trip the page monitor. Not good!
However, if you're careful about the pages you pick and use the page moni-
tors to best advantage, you can minimize the number of times information
traps trigger without providing any useful information.