Try It Out
If you want to check out the Yahoo Subjects plugin, do the following:
- How to setup the plugin:
- Start WBI
and setup your browser to use WBI as a proxy.
- Register the Yahoo Subjects plugin on the WBI console by
typing (on one line):
- Check to see whether the plugin is registered and enabled. Go to the
WBI Setup page. The YahooCategories plugin
should be listed in the table with a checkmark next to its name. If the plugin
is not listed, try registering it again. If the checkmark is not there, click
on the box to the left of the plugin name.
- Open another browser window. Use that window to try out the plugin, and use
this window to display the documentation. (To open another window using
Microsoft Internet Explorer, go to File -> New -> Window. To open a window
using Netscape Navigator, go to File -> New -> Navigator Window.)
- How to use the plugin:
What It Does
the web, you often want to go back to a specific page but cannot
remember the exact URL. Sometimes you know that it was two days
ago or that it was a Yahoo
category you want to get back to. Wouldn't it be nice to have a
tool that could list the relevant places you've visited (e.g.,
The Yahoo Subjects plugin is designed to keep track of the
Yahoo categories a user visits over time. The plugin monitors
the user while he or she is browsing the web. Whenever the user
visits a Yahoo subject (e.g., Computers &
Internet), the plugin keeps track of this category by
storing the URL of the Yahoo subject in a database. The entries
in this database can later be viewed on request.
How It Works
The Yahoo Subjects plugin is a combination of Megs that can monitor web content and produce HTML
pages using a Monitor and a Generator. The Monitor recognizes when the user visits a Yahoo category
and stores this event in a database. The generator is used to access the stored information and
produce a list of previously visited Yahoo categories. This list is a HTML resource that can be
displayed by the browser.
The figure illustrates the architecture of the Yahoo Subjects plugin. The Monitor will
log outgoing requests for Yahoo subjects in the database to maintain a list of subjects
that the user has visited previously. The Generator accesses the database and creates
the list of visted subjects that can then be displayed by the browser.
The Yahoo Category Monitor is used to recognize when a user visits a Yahoo category and if so, store
the category in the database. Using the Meg programming model, we can easily implement such a monitor
by subclassing the generic class HttpMonitor. The class YCategoryMonitor
monitors Yahoo categories. This monitor is setup such that it is invoked by WBI when the user visits the Yahoo
directory. The rule to configure the monitor is
When the user visits a Yahoo category the monitor gets invoked because the part of the URL that specifies
the host is always dir.yahoo.com. The Yahoo category monitor is invoked by calling its
void handleRequest(RequestEvent) method. This method extracts the name of the Yahoo
category and stores it in the database.
The Yahoo Category Generator is used to provide the user with the list of Yahoo categories he
previously visited. This generator is implemented by subclassing a generic Meg
(class HttpGenerator). The Yahoo Category generator produces the list of previously visited
categories on a user's request for the following URL:
WBI will invoke the yahoo category generator by calling the generator's
handleRequest(...) method. Therefore, the rule to configure the generator is:
In this handleRequest(...) method, the generator will access the database,
read the names of the previously visited Yahoo categories and
produce an HTML page. Each entry on this page provides references
to the category itself and and all its preceeding categories.
Storage and access to the names of the previously visited Yahoo categories is implemented
by using the classes Section class.
Some key WBI classes that were used:
- Contains the class definition for the Yahoo category tracker plugin.
- Contains the class definition for the Yahoo category monitor.
- Contains the class definition for the Yahoo category generator.
- Contains the necessary code to register the plugin with WBI. Registration is done through
WBI during runtime.
- This file.