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PICS PICS Frequently Asked Questions (FAQ)

This document provides answers to a number of Frequently Asked Questions about W3C's Platform for Internet Content Selection (PICS).

The PICS 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. More information about PICS is available from the PICS home page. The W3C's Resource Description Framework (RDF) may also be of interest as more general purpose successor technology to PICS.

A separate FAQ addresses intellectual freedom implications of PICS. The RDF FAQ may also be of interest.

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. Please note that 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.

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 of the PICS home page describing innovative uses of PICS labels

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.
$Date: 2003/01/02 13:57:27 $ by $Author: swick $
PICS FAQ as a separate document by: $Date: 2003/01/02 13:57:27 $