User's Guide
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Version 1.1 User's Guide |
| PICS Introduction |
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The PICS language lets web page authors create "labels" which describe the content of the document. A document's label provides a rating of that document's content according to any one of a number of PICS "rating systems".
A rating system is nothing more than a way to classify web content. Anyone can invent a rating system. For instance, when you go to the movies, you know what age range a movie is intended for, by checking its rating (G, PG, PG-13, R, X). This rating system was developed by the Motion Picture Association of America to describe the content of a film. The same rating system could be used to describe the content of web pages.
Movie critics have their own rating system for movies - a four star film is a "must-see", while zero star films are headed straight to video. So rating systems can be invented and applied to movies by persons other than the people responsible for producing the film. In the same way, third parties may also create PICS labels for a web page independent of the author of the page. In PICS terms, these third parties are referred to as "rating services".
The labels for a web page may be stored and transmitted along with the document (such as when you request a web page). Labels may also be served separately by other Internet-accessible web servers. Such web servers are called "label bureaus".
This is all interesting, but it is just groundwork required for PICS to filter content requests. PICS filtering selectively allows or blocks content based on the rating of each page within a particular rating system and the criteria established by a user or administrator.
To actually perform filtering, PICS checks the labels for the requested page or URL against "filters" to determine whether to allow or block the request. Filters are groups of "tests" where the administrator specifies what specific ratings from a particular rating system are allowable and which should be blocked. The filters, along with selected rating service(s) are part of a profile.
For example, the MPAA rating system rates films based on the suitable audience for the film, and assigns a rating of G, PG, PG-13, R or X. Assume that this rating system can be used with PICS to allow or block access to pages about each film based on the rating, and that pages with a rating of R or X should be blocked. The PICS profile to do this would be defined to use the MPAA rating service, and would have one filter. The filter would reject the page if it meets the criteria for one test- that the MPAA rating was greater than PG-13.
PICS also allows more complicated filtering. Say, for example, there are two rating services that rate films based on whether they are worth watching. One is called "Siskel" and the other is called "Ebert", and each only gives a rating of "thumbs-up" or "thumbs-down". Assume that these rating systems can be used with PICS to allow or block access to pages based on the rating, and that pages with a rating of "thumbs-down" from either service should be blocked. A PICS profile to do this would be defined to use both the Siskel and Ebert services. It would have one filter that would accept the page only if the criteria for both of two tests is met. One test would be that the Siskel rating is equal to "thumbs-up", and the other would be that the Ebert rating is equal to "thumbs-up".
The filter in the "Siskel and Ebert" profile could be defined instead to allow the page if the criteria for either of the two tests was met. This would allow any page that got a "thumbs-up" rating from either of the services, instead of only allowing pages that have a "thumbs-up" from both.
The details of the process that the WebDoubler PICS plug-in follows are a little more complicated than the examples. The filtering process is illustrated in the figure above.
The PICS plug-in examines each URL requested through WebDoubler, and it scans every file returned from remote Web servers. If a label bureau is specified, it connects to the bureau server to retrieve the labels for the requested URL. The PICS plug-in then checks this information against the tests defined within the filters in the active profile. If the URL is rejected, the PICS plug-in will return a message to the client that the request has been blocked by a PICS filter.
A profile may contain two different kinds of filters- URL filters and label filters. Label filters block access to pages based on the ratings contained in the pages' labels. To set up a label filter, you must choose at least one rating system, then define which ratings will be blocked and which will be allowed.
URL filters block requests based on the URL of the request itself. Each filter is based on a "URL pattern". URL patterns may be set up to block all URLs that are on a particular server, or contain a particular phrase. A URL filter could be defined to block all requests for URLs that contain "playboy", for example.
In its default configuration after it is installed, the PICS plug-in allows all web pages to be passed on to the web browser. In other words, it blocks nothing. You must create a profile and filter(s) to tell the PICS plug-in which pages should be blocked. We will provide step-by-step instructions for creating profiles later in this User's Guide.
The most common use of PICS protocols is to prevent access to web pages which have been rated as objectionable, obscene, or adult material. Web browsers such as Internet Explorer (3.0 or later) and Netscape Navigator (4.5 or later) understand the PICS language and can block access to web pages based on their rating. Without WebDoubler, this type of content filtering must be set up and configured in the web browser on that computer. To filter content for an entire group of users on multiple computers, you would need to manually configure each machine and make sure that each configuration is identical.
Using the WebDoubler PICS plug-in, you can set up content filters for an entire workgroup or classroom at one time. Using WebDoubler for filtering also prevents individual users from changing or disabling the filter because they do not have access to the machine doing the filtering.
WebDoubler also allows multiple profiles, which may be created and assigned to individual users or groups of users. This way different users or client computers in different locations can be assigned different levels of filtering.
There are a number of good on-line resources with PICS information. Starting points for additional details about PICS in general and specific information about the organizations and products that support PICS can be found at:
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