Content Selection (PICS)
The PICSTM specification enables
labels (metadata) to be associated with Internet content. It was originally
designed to help parents and teachers control what children access on the
Internet, but it also facilitates other uses for labels, including code
signing and privacy. The PICS platform is one on which other rating services
and filtering software have been built.
Table of Contents
For introductory materials, we suggest:
W3C maintains two electronic mailing lists for public use:
- [email protected] is where we distribute
public announcements related to the PICS project. Anyone may subscribe by
sending email to [email protected] with the word “Subscribe”
in the Subject: field.
- [email protected] is for the public to send questions about the
PICS also maintains special purpose mailing lists for
developers. There is also a PICS Interest Group for W3C
members and invited participants.
Information for the Media
For inquiries about PICS, please refer to
W3C’s press contact
Please direct technical inquiries to:
Inquiries about public policy issues surrounding content regulation may
also be directed to
Individuals and Organizations
Completed Specifications for PICS-1.1
These are official W3C recommendations. They are stable. The normative
specifications are in English. Translations of
some of these are available.
descriptions: Specifies the format for describing a
rating service’s vocabulary and scales; analogous to a database
- Label format
and distribution: Specifies the format of labels and
methods for distributing both self-labels and third-party labels.
Specifies an interchange format for filtering preferences, so that
preferences can be easily installed or sent to search engines.
- PICS Signed Labels
(DSig) 1.0 Specification: Specifies the syntax and
semantics of digital signatures in PICS labels.
Special Supplements to the Specifications
These are not official W3C recommendations, but they do represent a
consensus of the PICS working group.
- Default and Override Labels: Specifies what
a user agent (e.g., filtering software) should do when multiple labels are
available from the same service; Also suggests where filtering agents
should look for self-labels if they do not arrive in or along-with a
Resources for Developers of Software and Labeling Services
There is a low-volume mailing list, [email protected] for developers and
potential developers of PICS related products and services. To join this list,
send email to [email protected] and say why you’re interested in joining.
Resources for Software Developers
The technical specifications above are the most
important resource for developers. In addition:
Resources for Labeling Service Developers
To start a new labeling service, you will need to take the following
- Decide who will assign labels.
- Web site operators who self-label and/or
- A panel of raters that you recruit and/or
- A computer program that analyzes the contents of materials and
- Decide the labeling vocabulary and criteria
- Express the labeling vocabulary and criteria according to the format
specified in the technical specification.
You can create this file from scratch, or you can fill out web forms at
Application Incubator and the file will be created for you.
- Create the labels
- Arrange for distribution of your labels
- Give your labels to someone else who is running a PICS label bureau
- Run your own PICS label bureau and/or
- Convince web site operators to distribute the labels for their own
pages, either by putting them into HTML META tags or sending them
along with web pages.
- Give your labels to someone else who is running a PICS label bureau
Application Incubator project at the University of Michigan School of
Information will provide a limited amount of free technical consulting to
organizations that are considering establishing new labeling services.
Inventory [broken link as of July 2005].
Lorrie Cranor and Paul Resnick. This inventory was first
distributed at the December 1997 Internet On-line summit: Focus on Children.
The on-line version was updated until the summer of 1999. It also lists some
products and services that are not PICS-compatible.
The following resource lists are being maintained by members of the PICS
developers’ community. Contact the maintainer of each individual list with
additional links. The maintainers have all agreed to be fast and fair in
maintaining these lists (please send any unresolved complaints to
The most common uses of PICS labels have been in filtering products that
block access to certain materials based on labels associated with those
materials. The technology
inventory, however, identifies a range of other actions that can be taken
based on labels: suggest, search, inform, monitor/log, and warn.
Many authors and web site operators offer materials that they realize will
not be appropriate for all audiences. We encourage them to label their
materials to make it easier for filtering software to block access. As an
added inducement to labeling, we note that some future applications may use
labels for searching as well as filtering. Thus, labeling your site will make
it easier both for some audiences to avoid your site or documents and for
others to find you.
PICS is able to remain value-neutral by refusing to endorse any particular
labeling vocabulary. As a web site operator, you will not have that luxury.
You’ll want to adopt one or more of the rating vocabularies that other sites
are using. You may want to use one of the self-rating vocabularies.
Once you have created a label, you will need to distribute it along with
your document(s). PICS has defined several ways to do that. The recommended
method, if your HTTP server allows it, is to insert an extra header in the
HTTP header stream that precedes the contents of documents that are sent to
web browsers. The correct format, as documented in the specifications, is to
include the two headers, Protocol and PICS-Label:
The server can send these headers even if the browser has not specifically
The next best method is to run a label bureau at a specific location on
your server, as specified in a supplement to the
PICS specs, distributing labels only for documents on your server.
If neither of these methods is not available to you, a simpler but more
limited method is to embed labels in HTML documents using a META tag. With
this method, you will be able to send labels only with HTML documents, not
with images, video, or anything else. You may also find it cumbersome to
insert the labels into every HTML document. Some browsers, notably Microsoft’s
Internet Explorer versions 3 and 4, will download the root document for your
web server and look for a generic label there. For example, if no labels were
embedded in the HTML for this web page (they are), Internet Explorer would
look for a generic label embedded in the page at http://www.w3.org/ (generic
labels can be found there). Be sure to read the supplement for information on when specific labels
override generic labels and when they don’t.
The following is a an example of the right way to embed a PICS label in an
<head> <META http-equiv="PICS-Label" content=' (PICS-1.1 "http://www.gcf.org/v2.5" labels on "1994.11.05T08:15-0500" until "1995.12.31T23:59-0000" for "http://w3.org/PICS/Overview.html" ratings (suds 0.5 density 0 color/hue 1)) '> </head> ...contents of document here...
The following is incorrect, because the label is in the body of the
document rather than in the HTML header (delimited by <head> and
<head> </head> <META http-equiv="PICS-Label" content=' (PICS-1.1 "http://www.gcf.org/v2.5" labels on "1994.11.05T08:15-0500" until "1995.12.31T23:59-0000" for "http://w3.org/PICS/Overview.html" ratings (suds 0.5 density 0 color/hue 1))
'> ...contents of document here...
It is OK to include more than one META tag in a single HTML document, so
you can provide labels according to several services. There also is a way to
combine several labels into a single label list. See the technical specifications for details.
Separate W3C working groups are developing a new label format, called RDF;
the Resource Description Framework, based on XML. RDF labels will be able to express everything
that PICS labels can express, but will also permit string and structured
values, and some other nifty features. The latest information on this
available at http://www.w3.org/RDF.
A separate PICS FAQ
document is available, offering answers to a number of common questions about
PICS. In addition a separate FAQ addresses
intellectual freedom implications of PICS.
Comments to [email protected]
$Date: 2019/05/13 11:47:44 $ by $Author: swick $
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