Now, it is interesting to study the principal agents within the two main categories.
The goal of these agents is to help improve your monitoring of one or more Web sites and, eventually, the archives of discussion forums and mailing lists that interest you. Two possibilities are identified.
- Alert agents - via e-mail (Tracerlock, Mind-it from NetMind...) send you an e-mail each time the Web page that you have selected is modified, or when a search produces new results from one or more engines. In certain cases (Mind-it), it is also possible to filter the changes that take place by choosing adapted keywords and you can also receive the modified HTML page in your mailbox! These monitoring activities are often free and are managed by a distant server (you do not have any software to install on your computer). These agents are therefore very flexible and easy to use, but you cannot undertake very thorough or reliable monitoring activities.
- Off-line alarm agents are software clients that are installed on your computer and that you can personalize with precision in order to perform more advanced monitoring activities. First generation agents (Teleport Pro, WebWhacker, MemoWeb, etc.) allow you to copy whole sites on to your computer. You just have to indicate the address, and to set the time that you want them to activate. They will automatically connect to the network in order to download the data that interests you. They are truly " Web site rippers ". You can therefore undertake your search and monitoring activities on saved data (immediately visible), without needing to be connected directly to the Internet. Naturally, you do not need to capture whole sites, but only the parts that interest you. The agent alerts you each time something changes within your selection. The major inconvenience of these alarms is their lack of relevance. It is enough, for example, for a comma or an image to move to make the agent, not very intelligently, set off an alarm... Because of this, the second generation agents (Webspector, Website Watcher, C4U...) make it possible to filter the alarms better. With them, by using keywords, you can instruct your monitoring agent to alert you only when a relevant change occurs within the resources that it is monitoring. These electronic assistants are very useful, but you must be careful not to get submerged by a mass of data that could quickly paralyze your computer. In addition, learning how to train them is not always easy...
As we explained, push technologies are very effective, especially for following current events and disseminating information to homogeneous targets.
There are once more two identifiable types.
- The on-line push agents (My Yahoo, My News Page, My Excite, My AltaVista, Net.Portal, etc.) allow you to get personalized news in thematic categories (sports, politics, finance, weather, etc.) and many additional services (reservations, purchases, leisure, electronic communities...). All of this takes place on line and you do not need to install a software client. Information is served on a personal synopsis page, which is activated once you have defined your user profile. It is the principle of portal sites. This kind of service is simple and effective, but is very limited for sophisticated monitoring activities. Also, aside from the constraints related to Internet connection, the options for personalizing your page are often very limited (except My NewsPage from Individual).
- The off-line push agents are based on the same principle, but need you to install a software client (Marimba, BackWeb...) Therefore, once you have defined your profile from an increasingly rich list of options, your software automatically downloads, from a distant server, the contents of the subscribed channels. In addition, the principal browsers on the market have recently adopted a system of channels at the center of their navigation software.