PICS HOWTO - using PICS headers in HTML

PICS (Platform for Internet Content Selection), is a scheme allowing the rating of HTML and other documents for content, such as age-sensitive material. It is described in detail in the PICS homepage at W3.org.

Although not widely deployed (October 1996), the inclusion of PICS in Internet Explorer may promote its acceptance by a wider clientele. See this Feb 97 PC Week article.

This note addresses some of the issues of rating pages in practice, and using the PICS features built into Internet Explorer.

Introduction

PICS works by comparing PICS information from an HTML META tag or HTTP header with a rating file installed in the browser. Typically, the rating file is provided by a Rating Service, who also provide a script to generate PICS headers suitable for inclusion in a document.

PICS for Users

While PICS is vendor and platform-independant, the major browser currently with PICS support is Internet Explorer.

In Internet Explorer, the PICS settings are found under View --> Options --> Security: Content Advisor. Internet Explorer comes preloaded with the RSAC ratings file, which is usually located in C:\WINDOWS\System\Rsaci.rat. You should be able to view this file with Notepad or other text editor; the syntax is described here at W3.org.

More than one ratings file can be installed.

To install a new ratings file, download the file from the ratings service (for example, VWP1.0.rat here) into the C:\WINDOWS\System directory (actually, it doesn't matter where, but this is the default). It should have a .rat extension. Next, in Content Advisor --> Settings --> Advanced --> Ratings Systems, select Add, then the new ratings file, then OK. Returning to the Content Advisor --> Ratings menu, you will see entries for the new ratings scheme. Typically a list of topics is presented with a slider bar for each. Move the slider bar to the highest setting in each category you wish to be able to view. You should be able to contact the ratings service for more information by clicking the More Info button (for example, VWP1.0 here).

When the Content Advisor is enabled, you can select (in Settings --> General) whether to allow viewing of unrated sites. If you select Yes, then only pages with a PICS rating exceeding your preset limits will be blocked. Unrated sites will not be blocked, no matter what their content.
If you select No, then only pages with a PICS rating can be viewed. If a page is rated with a scheme you do not have installed, you will see a message telling you how to contact the rating service. You should then receive instructions on downloading the ratings files; if not, try here at W3.org. If a page is rated with two schemes, and you have only one installed, you will not see any message. If you have both schemes installed, then the limits of both schemes must be met before a page can be viewed. A message will be shown explaining which limit(s) are exceeded. If the header for one scheme is invalid or has expired, but the other is valid, you will see no message (unless the ratings are over limit). If all the headers are invalid or expired, you will see a warning message.

At this time (IE version 3.0), only Web pages appear to be checked by Internet Explorer, though the PICS protocol may be applied to other media such as Usenet messages, IRC channels, chat rooms, etc.. As a rating method, it is sufficiently flexible to be extended to other electronic media such as CD-ROMs, and conceivably audio CDs, television programs and the like.

PICS for Content Developers

For a content developer, installing PICS usually means running a PICS generator such as this one, and including the resulting META data in the document header.

PICS allows for generic and specific labels. Generic labels apply to any document whose URL begins with a specific string of characters. Specific labels apply only to a given file.

In version 3.0 of Internet Explorer, the browser first checks the document itself for PICS data as Metadata in the document head, and also as an HTTP header. If this does not exist, it gets the homepage for the site (formed by stripping all path and filenames from the URL) and checks that. It does not check for an index page in the current directory. Thus in Internet Explorer, specific labels override generic labels. The only generic label is that of the homepage. Note that where a for option is used, in declaring a generic label, that the specified URL must match the one that the user sees. This may not always be the case when a server has more than one name, or is addressed by a short from from within the users domain.

Using more than one rating service

PICS labels may be concatenated, for instance: 
<HTML><HEAD><TITLE>Joes Bookstore</TITLE>
<META http-equiv="PICS-Label" content='(PICS-1.1 
"http://www.service1.org/v1.0"
  labels on "1996.10.05T05:15-0500"
  for "http://www.my.org/etc/mypage.html"
  ratings (s 0 v 0 g 0)
"http://www.service2.org/v1.2"
  labels on "1996.10.05T08:15-0700"
  for "http://www.my.org/etc/mypage.html"
  ratings (com 2 edu 1)
)'>
</HEAD>
Although HTML allows more than one META tag of one type, Internet Explorer does not currently support this.

Note that if the user only has one scheme installed, that no message will be generated if that one is under limits (the second scheme will be ignored).

Applying PICS headers to a non-HTML document

It is possible to apply a PICS header to a file such as a movie, PDF or VRML file by generating an HTTP header. Some servers, such as Apache or CERN httpd allow the use of a metafile attached to a document which contains extra HTTP headers not normally generated by the server. A header such as 
PICS-Label: (PICS-1.1 "http://www.service2.org/v1.2" r (s 0 v 0 g 0))
may be specified. Internet Explorer does not appear to support this use inside a /cgi-bin/ directory, though. (A METAdata header may be generated instead).

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