PICS

Platform for Internet 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. Parents who are interested in finding filtering software or ISPs that offer filtering will probably want to consult www.netparents.org rather than this site.

Table of Contents

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Introduction

For introductory materials, we suggest:

Participating

W3C maintains two electronic mailing lists for public use:

  • PICS-info@w3.org is where we distribute public announcements related to the PICS project. Anyone may subscribe by sending email to PICS-info-request@w3.org with the word "Subscribe" in the Subject: field.
  • PICS-ask@w3.org is for the public to send questions about the PICS project.

PICS also maintains special purpose mailing lists for developers. There is also a PICS Interest Group for W3C members and invited participants.

What's New

Information for the Media

Press inquiries about PICS should be directed to any of the following people:

Technical inquiries to:

Inquiries about public policy issues surrounding content regulation may also be directed to

What others are saying about PICS

Governments

Media

Individuals and Organizations

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PICS Technical Specifications

Completed Specifications for PICS-1.1

These are official W3C recommendations. They are stable.

  1. Service descriptions: Specifies the format for describing a rating service's vocabulary and scales; analogous to a database schema.
  2. Label format and distribution: Specifies the format of labels and methods for distributing both self-labels and third-party labels.
  3. PICSRules: Specifies an interchange format for filtering preferences, so that preferences can be easily installed or sent to search engines.

These are proposed W3C recommendations. They may still change.

  1. 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.

  1. 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 document.

Resources for Developers of Software and Labeling Services

There is a low-volume mailing list, pics-interest@w3.org for developers and potential developers of PICS related products and services. To join this list, send email to pics-ask@w3.org 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 steps:

  1. 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 assigns labels
  2. Decide the labeling vocabulary and criteria
  3. 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 the PICS Application Incubator and the file will be created for you.
  4. Create the labels
  5. Arrange for distribution of your labels
    • Give your labels to someone else who is running a PICS label bureau and/or
    • 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.

The PICS 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.

Lists of PICS-compatible products and services.

Technology Inventory. 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 pics-ask@w3.org).

Innovative Uses of PICS Labels

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.

Hints for Web Site Authors Who Want to Self-Label

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:

HTTP/1.0 200 OK
Date: Thu, 30 Jun 1995 17:51:47 GMT
Last-modified: Thursday, 29-Jun-95 17:51:47 GMT
Protocol: {PICS-1.1 {headers PICS-Label}}
PICS-Label:
 (PICS-1.1 "http://www.gcf.org/v2.5" labels
  on "1994.11.05T08:15-0500"
  exp "1995.12.31T23:59-0000"
  for "http://www.greatdocs.com/foo.html"
  by "George Sanderson, Jr."
  ratings (suds 0.5 density 0 color/hue 1))
Content-type: text/html

...contents of foo.html...

The server can send these headers even if the browser has not specifically request them.

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 HTML document:

RIGHT!

<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>).

WRONG!

<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.

RDF

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.

Frequently Asked Questions

In addition the questions and answers below, a separate FAQ addresses intellectual freedom implications of PICS.

Common Misconceptions

Q: Where do I get the PICS software? How much does PICS cost?

A: Actually, PICS doesn't provide any software. It's just a set of technical specifications that help software and rating services to work together. You would actually use filtering software provided by some organization other than PICS. There is a list of PICS-compatible client software, but W3C does not endorse or evaluate any of the products. Prices vary; some software is free.

Q: I have lost or forgotten the password to change my filtering preferences. Can W3C help me?

A: We are sorry, but the World Wide Web Consortium has no way to help with specific product support. You will need to contact the vendor of your software.

Q: What criteria does PICS use in deciding what's safe for my children to view? Isn't that inherently a subjective decision?

A: Again, PICS doesn't actually rate anything. PICS just sets technical specifications so that ratings from any source will work with all the filtering software. Rating and labeling services choose their own criteria for rating. Since rating will always involve some amount of subjective judgement, you'll want to choose a rating service whose judgements are close to the ones you would make. The filtering software you use may already be configured to use a particular rating service, so you may not have to make this choice separately.

Q: What is PICSRules?

A: PICSRules is a language for expressing filtering rules (profiles) that allow or block access to URLs based on PICS labels that describe those URLs. The purposes for a common profile-specification language are:

    Sharing and installation of profiles. Sophisticated profiles may be difficult for end-users to specify, even through
    well-crafted user interfaces. An organization can create a recommended profile for children of a certain age. Users who
    trust that organization can install the profile rather than specifying one from scratch.  It will be easy to change the active
    profile on a single computer, or to carry a profile to a new computer.
    Communication to agents, search engines, proxies, or other servers. Servers of various kinds may wish to tailor
    their output to better meet users' preferences, as expressed in a profile. For example, a search service can return only
    links that match a user's profile, which may specify criteria based on quality, privacy, age suitability, or the safety of
    downloadable code.
    Portability betwen filtering products. The same profile will work with any PICSRules-compatible product.

How to label

Q: How difficult is it for a content provider to include a PICS compliant label with the content? Please describe the process.

A: A content provider first needs to choose which rating vocabulary to use. We recommend that you use a vocabulary used by others, to make it easy for end-users to understand your labels. A list of self-rating vocabularies is available, but W3C does not endorse any particular vocabulary. Typically, you choose a self-labeling service, connect to its web server and describe your document or web site by filling out an on-line questionnaire. After completing the questionnaire, the service gives you a text label in a special format, which you then paste into the header portion of your HTML document (or the home page for your site).

Q: I have read that an independent rating agency can label sites or documents created by others. Do the documents' creators have to cooperate? Please describe the process.

A: An independent rating agency need not get cooperation from every publisher whose material it labels. As with self-labeling describeed above, the independent labeler first needs to invent or adopt an existing vocabulary. The rater then uses a software tool to create labels that describe particular URLs. Instead of pasting those labels into documents, the independent rater distributes the labels through a separate server, what we call a label bureau. Filtering software will know to check at that label bureau to find the labels, much as consumers know to read particular magazines for reviews of appliances or automobiles.

Q: Can I create my own labels so that I can be sure that my child is only viewing material which I have reviewed?

A: An individual who sets access controls can also act as an independent rating agency. Some filtering software facilitates this process by storing such labels on the local computer, bypassing the need for a label bureau. Filtering software typically describe this feature as an "override" capability.

How filtering works

Q: I understand that a browser or stand-alone software filter can be set to check labels supplied by an independent rating agency before connecting to a chosen site. Can you explain how this works?

A: When an end-user asks to see a particular URL, the software filter fetches the document but also makes an inquiry to the label bureau to ask for labels that describe that URL. Depending on what the labels say, the filter may block access to that URL.

Q: Does using a PICS compliant software filter slow communication with the Internet?

A: If the filter asks a label bureau for labels, as described above, the extra request will take extra time. There are various techniques, including keeping local copies of labels and making parallel requests, that can reduce this performance penalty. This is likely to be a point of significant competition between vendors.

Q: Can an Internet access service provider limit access for all subscribers to things labeled a particular way or can PICS compliant labels only be used to limit access at the user level? Can a country limit access to all its Internet access service providers to particular categories of labels?

A: That depends on how the network is configured. If an access provider, or a country, has choke points through which all requests travel, it could install the filtering software at the choke points. It is a more natural and effective use of the technology to put control in the hands of end-users, because different users will want to limit access to different things.

Q: Does PICS recommend any particular software filter?

A: No. The World Wide Web Consortium, which developed PICS, is strictly vendor neutral.

Q: I am worried that some classification systems may occasionally mislabel adult material as suitable for a child. I would feel confident if two separate classification systems both labeled the material as suitable for a child. Can I use a PICS compliant software filter to only permit access to material that has appropriate labels from two classification systems?

A: In principle, a filter can pay attention to labels from more than one source. The actual implementation may vary from vendor to vendor.

Q: I run a small business and several of my employees require regular access to a few Internet sites. Can I label those sites and run a software filter to ensure that my employees do not access any other sites? Is that difficult to do? How much time will it take me?

A: Many vendors offer a "block unrated sites" option. The difficulty of creating your own zone of acceptable materials for employees will vary from vendor to vendor. We also expect teachers and textbook publishers to create lesson-specific zones of the Internet. At least one vendor has adopted this "inclusive" method as its general filtering technique.

Advanced questions

Q: How can I find out if a site (say mine) has been rated by a label bureau, and what the rating is?

A: If you know the URL that the label bureau responds (and it doesn't require you to pay a subscription charge), you can just send it the appropriately formated URL and check the response. Or, you can just fill out a web form at the Test-a-URL site created by the PICS Application Incubator project at the University of Michigan School of Information.

Q: If the content contains the label, can the label be altered or removed from the content?

A: Yes, a label in an HTML document can be removed. Embedding a label in a document requires the cooperation of the publisher and all those who handle the document.

Q: If the label and content are physically separated, how are they reliably linked to each other? What happens if the content is moved or cached to another site?

A: A label bureau that stores only labels and not documents associates the labels with URLs. Even if the contents retrieved from that URL are cached, the label bureau can still provide a label describing the URL. If the contents are moved to a new URL, the label bureau may try to keep track of synonyms (alternate URLs that point to the same document) but it may not always keep up. A document that has been labeled at one URL may effectively be unlabeled if it moves to another URL.

Q: Does PICS work with communication protocols other than http? In other words, can a PICS compliant software filter be defeated by a user whose access is restricted to documents of a certain label classification, through the user obtaining other documents by FTP or E-mail?

A: PICS labels can describe anything that can be named with a URL. That includes FTP and Gopher. E-mail messages do not normally have URLs, but messages from discussion lists that are archived on the Web do have URLs and can thus be labeled. A label bureau will need to distribute labels for non-HTTP URLs, because there is no protocol defined for passing labels along with these other protocols or for embedding labels in non-HTML documents.

Q: Can PICS compliant labels be attached to particular IRC channels and Usenet discussions?

A: Usenet newsgroups, and even individual messages, have URLs, and hence can be labeled. There is not yet an official URL scheme for IRC, but the PICS specifications defined a preliminary scheme, and a more robust URL scheme for IRC is being worked on.

Q: How can I be sure that a PICS label is not false or misleading? Can a digital signature be attached to the label so that I can be sure that the label is genuine?

A: A label can include a cryptographic signature. This mechanism lets you check that the label was authorized by the service you subscribed to. You have to decide for yourself whether the service is trustworthy; if it frequently puts out misleading labels, you probably will want to switch to another rating service.

Q: How can I be sure that the content of a site has not changed since it was labeled?

A: A label can include a cryptographic checksum on the contents of the document. If the checksum matches a checksum of the current contents, then the label is valid. If not, then the document has changed since the label was created.

Q: How can you distinguish bewteen changes to a site that invalidate the label and changes that do not?

A: Unfortunately, you can't tell in general. A client may choose to trust a label even if the contents of a document have changed since the label was created. A labeling service that is confident its label will still be valid even if changes are made to the contents, perhaps because it trusts the author, can omit the cryptographic checksum from the label. In that case, the labeler is strongly encouraged to include an expiration date in the label.

Q: Can I ask a search service to omit responses that will be blocked by my filter?

A: See the section on innovative uses of labels, in this document.

Q: Setting the filtering rules is too much of a bother for me. Can't I just find someone I trust and install their rules.

A: Not yet, but we hope that vendors will implement this feature soon. This was one of the primary motivations for defining the PICSRules interchange format for filtering rules, so that you'd be able to easily import and install filtering rules created by someone else that you trust.

Do you have a question not answered in this FAQ? If so, please send email to pics-ask@w3.org.


Comments to PICS-ask@w3.org.

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