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<H3 align=right>
  REC-PICS-services-20091124
</H3>
<H1 align=center>
  Rating Services and Rating Systems (and Their Machine Readable Descriptions)
</H1>
<P>
<H3 align=center>
  Version 1.1
</H3>
<H3 align=center>
  W3C Recommendation 31-October-96 (revised 24-Nov-2009)
</H3>
<DL>
  <DT>
  <DT>
  <DT>
    Editor:
  <DD>
    Jim Miller <A HREF="mailto:jmiller@w3.org">&lt;jmiller@w3.org&gt;</A>
  <DT>
    Authors:
  <DD>
    Jim Miller
    <A HREF="mailto:jmiller@w3.org">&lt;jmiller@w3.org&gt;</A><BR>
    Paul Resnick
    <A HREF="mailto:presnick@research.att.com">&lt;presnick@research.att.com&gt;</A><BR>
    David Singer
    <A HREF="mailto:singer@almaden.ibm.com">&lt;singer@almaden.ibm.com&gt;</A>
  <DD>
</DL>


<p style="border: solid thick red; padding: 1em"><strong>Note:<em>This paragraph is informative.</em> This document is
currently not maintained. PICS has been superseded by the Protocol for Web Description Resources (<a href="/2007/powder/">POWDER</a>). W3C encourages authors and
implementors to refer to POWDER (or its successor) rather than PICS when developing systems to describe Web content or agents to
act on those descriptions. A brief document outlining the advantages offered by POWDER compared with PICS is <a href="/2009/08/pics_superseded.html">available
separately</a>.</strong> The <a href="/TR/REC-PICS-services-961031">31 October 1996 PICS Recommendation</a> remains available on the W3C Web site.</p>


<P>
  <HR>
<H3>
  Status of this document
</H3>
<P>
This document has been reviewed by W3C members and other interested parties
and has been endorsed by the Director as a W3C Recommendation. It is a stable
document and may be used as reference material or cited as a normative reference
from another document. W3C's role in making the Recommendation is to draw
attention to the specification and to promote its widespread deployment.
This enhances the functionality and interoperability of the Web.
<P>
A list of current W3C Recommendations and other technical documents can be
found at
<A href="http://www.w3.org/pub/WWW/TR/">http://www.w3.org/pub/WWW/TR/</A>.
<P>
<H2>
  Abstract
</H2>
<P>
This document, which has been prepared for the technical subcommittee of
<A href="http://w3.org/PICS">PICS (Platform for Internet Content
Selection)</A>, defines a language for describing rating services. Software
programs will read service descriptions written in this language, in order
to interpret content labels and assist end-users in configuring selection
software.
<H2>
    <HR>
  <P>
  Table of Contents
</H2>
<P>
<A HREF="#Introduction">Introduction</A>
<P>
<A HREF="#Rating Service">What is a "rating service"?</A>
<P>
<A HREF="#Rating System">What is a "rating system"?</A>
<P>
<A HREF="#Content Label">What is a "content label"?</A>
<P>
<A HREF="#Document type">The <SAMP>application/pics-service</SAMP> document
type</A>
<P>
<A HREF="#Explanation">Explanation of Sample Rating Service</A>
<P>
<A HREF="#Syntax">Detailed syntax of
<SAMP>application/pics-service</SAMP></A>
<P>
<A HREF="#Glossary">Glossary </A>
<P>
<A HREF="#References">References</A>
<P>
<A HREF="#Acknowledgements">Acknowledgments</A>
<P>
<A HREF="#Appendix A">Appendix A: The Ages Rating Service</A>
<P>
<A HREF="#Appendix B">Appendix B: RSAC Rating Service</A>
<P>
<A HREF="#Appendix C">Appendix C: The SafeSurf~~ Rating Service</A>
<P>
<P>
  <HR>
<H2>
  <A NAME="Introduction">Introduction</A>
</H2>
<P>
This document, which has been prepared for the technical subcommittee of
<A href="http://w3.org/PICS">PICS (Platform for Internet Content
Selection)</A>, defines a language for describing rating services. Software
programs will read service descriptions written in this language, in order
to interpret content labels and assist end-users in configuring selection
software.
<P>
A related document (<A HREF="REC-PICS-labels-961031.html">PICS Label
Distribution</A>) specifies the syntax and semantics of content labels and
protocol(s) for distributing labels.
<P>
The goal of the <A href="http://w3.org/PICS">PICS effort</A> is to enable
a marketplace in which many different products and services will be developed,
tested, and compared. Hence, the following considerations have had significant
impact on this document:
<UL>
  <LI>
    Some organizations may rate items on well-known dimensions, using their own
    techniques and viewpoints to determine actual ratings. Other organizations
    may choose to develop their own dimensions for rating. This motivates the
    distinction between a <I>rating system</I> and a <I>rating service</I> (see
    the <A href="#Glossary">glossary</A>).
  <LI>
    Some services may provide access to their ratings on-line, from an HTTP server,
    while others may either ship them in batches or transmit them on floppy disks
    or CD-ROMs.
</UL>
<H2>
  <A NAME="Rating Service">What is a "rating service"?</A>
</H2>
<P>
A <I>rating service</I> is an individual, group, organization, or company
that provides content labels for information on the Internet. The labels
it provides are based on a rating <I>system</I> (see below). Each rating
service must describe itself using a newly created MIME type,
<TT>application/pics-service</TT>. Selection software that relies on ratings
from a PICS rating service can first load the
<TT>application/pics-service</TT> description. This description allows the
software to tailor its user interface to reflect the details of a particular
rating service, rather than providing a "one design fits all rating services"
interface.
<P>
This specification does not state how the <TT>application/pics-service</TT>
description of a rating service is initially located. For users of the World
Wide Web, we expect that well-known sites will provide lists of rating services
along with their <TT>application/pics-service</TT> descriptions. It is expected
that client programs will cache copies of <TT>application/pics-service</TT>
descriptions, so any incompatible change in a service description should
be accomplished by creating an entirely new service URL.
<P>
Each rating service picks a URL as its unique identifier. It is included
in all content labels the service produces, to identify their source. We
recommend, but do not require, that this identifier include a version number,
as shown in all of the examples in this specification, to simplify transitions
due to incompatible changes over time. For example, our sample service
"http://www.gcf.org/v1.0/" includes "v1.0" as its own version number. To
ensure that no other service uses the same identifier, it must be a valid
URL. In addition, the URL (when used within a query) serves as a default
location for a label bureau that dispenses this service's labels (see
<A HREF="REC-PICS-labels-961031.html">PICS Label Distribution</A>).
<P>
Since the service identifier is a URL, it can be used to retrieve a document.
That document may be in any format, but we recommend that it:
<UL>
  <LI>
    be in HTML format;
  <LI>
    be organized for ease of use by novice computer users (the
    <TT>application/pics-service</TT> description would be a poor choice);
  <LI>
    describe not only the rating service, but the rating system as well (or provide
    a link to another document describing the rating system);
  <LI>
    be available in multiple languages, either through an existing negotiation
    mechanism or through links to alternate language versions;
</UL>
<H2>
  <A NAME="Rating System">What is a "rating system"?</A>
</H2>
<P>
A rating <I>system</I> specifies the dimensions used for labeling, the scale
of allowable values on each dimension, and a description of the criteria
used in assigning values. For example, the MPAA rates movies in the USA based
on a single dimension with allowable values G, PG, PG-13, R, and NC-17.
<P>
Each rating system is identified by a valid URL. This enables several services
to use the same rating system and refer to it by its identifier. The URL
naming a rating system can be accessed to obtain a human-readable description
of the rating system. The format of that description is not specified.
<H2>
  <A NAME="Content Label">What is a "content label"?</A>
</H2>
<P>
A<I> content label</I> (or <I>rating</I>) contains information about a document.
As described in <A HREF="REC-PICS-labels-961031.html">PICS Label
Distribution</A>, a content label (or rating) has three parts:
<OL>
  <LI>
    the URL naming the rating service that produced the label;
  <LI>
    a set of PICS-defined (and extensible) attribute-value pairs, which provide
    information about the rating such as the date that the rating was assigned;
  <LI>
    a set of rating-system-defined attribute-value pairs, which actually rate
    the item along various <I>dimensions</I> (also called <I>categories</I>)
</OL>
<H2>
  <A NAME="Document type">The <SAMP>application/pics-service</SAMP> document
  type</A>
</H2>
<P>
A rating service is defined by a document of type
<TT>application/pics-service</TT>. The detailed syntax and semantics are
presented in the next two sections. Here is an example of such a document,
intended only to illustrate the full set of features of a machine description:
<PRE>
<TT>((PICS-version 1.1)</TT>
<TT> (rating-system "http://www.gcf.org/ratings")</TT>
<TT> (rating-service "http://www.gcf.org/v1.0/")</TT>
<TT> (icon "icons/gcf.gif")</TT>
<TT> (name "The Good Clean Fun Rating System")</TT>
<TT> (description "Everything you ever wanted to know about soap,</TT>
<TT>cleaners, and related products.  For demonstration purposes only.")</TT>
<TT></TT>
<TT> (category  </TT>
<TT>  (transmit-as "suds")</TT>
<TT>  (name "Soapsuds Index")</TT>
<TT>  (min   0.0)</TT>
<TT>  (max   1.0))</TT>
<TT></TT>
<TT> (category  </TT>
<TT>  (transmit-as "density")</TT>
<TT>  (name "suds density")</TT>
<TT>  (label (name "none") (value 0) (icon "icons/none.gif"))</TT>
<TT>  (label (name "lots") (value 1) (icon "icons/lots.gif")))</TT>
<TT></TT>
<TT> (category  </TT>
<TT>  (transmit-as "subject")</TT>
<TT>  (name "document subject")</TT>
<TT>  (multivalue true)</TT>
<TT>  (unordered true)</TT>
<TT>  (label (name "soap") (value 0))</TT>
<TT>  (label (name "water") (value 1))</TT>
<TT>  (label (name "soapdish") (value 2))</TT>
<TT>  (label-only))</TT>
<TT></TT>
<TT> (category  </TT>
<TT>  (transmit-as "color")</TT>
<TT>  (name "picture color")</TT>
<TT>  (integer)</TT>
<TT></TT>
<TT>  (category  </TT>
<TT>    (transmit-as "hue")</TT>
<TT>    (label (name "blue")  (value 0))</TT>
<TT>    (label (name "red")   (value 1))</TT>
<TT>    (label (name "green") (value 2)))</TT>
<TT></TT>
<TT>  (category  </TT>
<TT>   (transmit-as "intensity")</TT>
<TT>   (min 0)</TT>
<TT>   (max 255))))</TT>
<TT></TT>
<TT></TT>

</PRE>
<H2>
  <A NAME="Explanation">Explanation of Sample Rating Service</A>
</H2>
<P>
<OL>
  <LI>
    The identifier of the rating system used is http://www.gcf.org/ratings. The
    document available at that URL should be a human-readable description of
    the categories, scales, and intended criteria for assigning ratings.
  <LI>
    The identifier of the rating service is http://www.gcf.org/v1.0/. The labels
    themselves will have this URL in them to identify the service that created
    them. The document available at this URL should be a human-readable description
    of the rating service.
  <LI>
    There is an icon associated with the rating service, and it can be retrieved
    from "http://www.gcf.org/v1.0/icons/gcf.gif" (formed by interpreting the
    <B>icon</B> attribute's value relative to the <B>rating-service</B> identifier).
  <LI>
    There are four top-level categories in this rating system. Each category
    has a short transmission name to be used in labels; some also have longer
    names that are more easily understood. For example, the first has transmission
    name "suds" and the longer name "Soapsuds Index." The second has a transmission
    name of "density" and longer name "suds density,".
  <LI>
    The "Soapsuds Index" category is rated on a scale from 0.0 to 1.0, inclusive.
  <LI>
    The "suds density" category can have ratings from negative to positive infinity,
    but there are two values that have names and icons associated with them.
    The name "none" is the same as 0, and the name "lots" is the same as 1. Icons
    associated with those names are found at
    http://www.gcf.org/ratings/icons/none.gif and
    http://www.gcf.org/ratings/icons/lots.gif (i.e. they are dereferenced relative
    to the <B>rating-system</B> identifier).
  <LI>
    The "document subject" category only allows the values 0, 1, and 2 to be
    used, but a single document can have any combination of these values. Each
    value has a name (0 is "soap," etc.). So one document might not have any
    rating on this category, while another is both a "soap" and a "soapdish."
    The values are unordered, which is a hint to user interface designers to
    employ check boxes or some other widgets that do not convey ordering of values,
    rather than a slider or other widget that does convey ordering.
  <LI>
    The "picture color" category has two sub-categories. Values on the "picture
    color" dimension itself are restricted to integers, and will be transmitted
    as a category named "color." The first sub-category is transmitted as "color/hue"
    and the second as "color/intensity." Notice that color/hue can take on only
    integer values (because it inherits the <B>integer</B> attribute of its parent,
    "color," category), but there are three values with names ("blue," "red,"
    and "green."). The category color/intensity can take on any integer value
    between 0 and 255 (inclusive).
</OL>
<H2>
  <A NAME="Syntax">Detailed syntax of
  <SAMP>application/pics-service</SAMP></A>
</H2>
<P>
<B>Notes:</B>
<OL>
  <LI>
    Whitespace is ignored except in quoted strings. Multiple contiguous whitespace
    characters can be treated as though they were a single space character.
  <LI>
    <B>Transmit-name</B>s and quoted strings are case sensitive. Option names
    and other tokens in the BNF grammar are case insensitive.
  <LI>
    Additional attributes may be added over time, using the <EM>extension</EM>
    attribute. To avoid duplication of extension names, each extension is identified
    by a <I>quoted-URL</I>. The URL can be dereferenced to get a human-readable
    description of the extension. If the extension is <B>optional</B> then software
    which does not understand the extension can simply ignore it; if the extension
    is <B>mandatory</B> then software which does not understand the extension
    should reject the entire service description. See
    <A href="http://w3.org/PICS/extensions/"> http://w3.org/PICS/extensions/</A>
    to find out what extensions are currently in use.
  <LI>
    The only <EM>service-option</EM> that may occur more than once in a single
    service description is the <EM>extension</EM> option. Likewise, the only
    option that may occur more than once as a <EM>default</EM> or as a
    <EM>category-option</EM> is <EM>extension</EM>. In each case, if the
    <EM>extension</EM> option is supplied more than once, the
    <EM>quoted-URL</EM>s defining the extensions must be distinct.
  <LI>
    This specification requires the use of
    <A href="ftp://ds.internic.net/rfc/rfc1642.txt">UTF-7 encoding</A> to allow
    for the inclusion of non-English description strings. For those rating systems
    and services that use only the US-ASCII character set in their descriptive
    strings, UTF-7 allows direct encoding of the following (printable) characters:
    a-z, A-Z, 0-9, '(),-./:?!#$%&amp;*;&lt;=&gt;@[]^_`{|} Notice that "+" is
    <I>not</I> included in this set, since it is used by the UTF-7 encoding system.
  <LI>
    It is guaranteed that this and all future versions of the
    <TT>application/pics-service</TT> MIME type will begin with the
    <I>version</I> information, changing from 1.1 as specified here to other
    numbers as the specification is revised. Rating services are encouraged to
    adopt a similar mechanism and place their own version number in their
    <I>rating-service</I> URL. (Notice that the service description uses the
    notation "(PICS-version 1.1)" while the label itself (see
    <A href="http://w3.org/PICS/labels.html">PICS Label Distribution</A>) uses
    "PICS-1.1". While inelegant, this is intentional.)
</OL>
<PRE>
<B>rating-service-description ::</B>
  '(' <I>version</I> <I>rating-system</I> <I>rating-service</I>
      <I>service-option</I>* <I>category-list</I>+ ')'

<B>version ::</B> '(' 'PICS-version' '1.1' ')'
<B>rating-system ::</B> '(' 'rating-system' <I>quoted-URL</I> ')'
<B>rating-service ::</B> '(' 'rating-service' <I>quoted-URL</I> ')'
<B>service-option ::</B> <I>default</I> | <I>description</I> | <I>extension</I>
  <I>icondef</I> | <I>name</I>
<B>category-list ::</B>
  '(' 'category'
      '(' 'transmit-as' <I>transmit-name</I> ')'
      (<I>category-option</I> | <I>scale-option</I>)*
      <I>category-list</I>*
  ')'

<B>defaultable-option ::</B> <I>extension</I> | <I>integer</I> | <I>labeled</I>
   | <I>max</I> | <I>min</I> | <I>multi</I> | <I>unordered</I>
<B>category-option ::</B>  <I>description</I> | <I>icondef</I> | <I>name</I>
<B>scale-option ::</B> <I>defaultable-option</I> | <I>enum-list</I>
<I></I>
<B>enum-list ::</B> <I>enum</I>+
<B>enum ::</B>
   '(' 'label' <I>name</I> [<I>description</I>]
       '(' 'value' <I>number</I> ')'
       [<I>icondef</I>]
   ')'

<B>default ::</B> '(' 'default' <I>defaultable-option</I>+ ')'
<B>description ::</B> '(' 'description' <I>quoted-string</I> ')'
<B>extension ::</B> '(' 'extension'
                 '(' <I>mand/opt</I> <I>quoted-URL</I> <I>data</I>* ')' ')'
<B>icondef ::</B> '(' 'icon' <I>quoted-URL</I> ')'
<B>integer ::</B> '(' 'integer' [<I>boolean</I>] ')'
<B>labeled ::</B> '(' 'label-only' [<I>boolean</I> ] ')'
<B>max ::</B> '(' 'max' <I>maxnum</I> ')'
<B>min ::</B> '(' 'min' <I>minnum</I> ')'
<B>multi ::</B> '(' 'multivalue' [<I>boolean</I>] ')'
<B>name ::</B> '(' 'name' <I>quoted-string</I> ')'
<B>unordered ::</B> '(' 'unordered' [<I>boolean</I>] ')'

<B>boolean ::</B> 't' | 'f' | 'true' | 'false'
<B>mand/opt ::</B> 'optional' | 'mandatory'
<B>transmit-name ::</B> '"' <I>transmit-name-char</I>+ '"'

<B>minnum :: </B><I>number</I> | '-INF'
<B>maxnum :: </B><I>number</I> | '+INF'
<B>number ::</B> [<I>sign</I>]<I>unsignedint</I>['.' [<I>unsignedint</I>]]
<B>sign ::</B> '+' | '-'
<B>unsignedint :: </B>[0-9]+

<B>data ::</B> <I>quoted-string</I> | '(' <I>data</I>* ')'
    <B>Note:</B> In many cases it is useful to be able to use a
    URL as data.  This syntax requires that, in such a case,
    the URL must be UTF-7 encoded.  This will rarely require
    any additional work, but designers and implementers of
    extensions should take care.
<B>quoted-string ::</B> '"' <I>UTF-7</I> '"'
<B>UTF-7 ::</B> Characters encoded using UTF-7, with direct
   coding of US-ASCII set O <I>except</I> for the double-quote
   (decimal 34) which must be encoded to allow for its use
   as the string delimiter character.  See note above.

<B>quoted-URL :: </B> '"' URL '"'
<B>URL</B> is as defined in RFC-1738 for URLs. In addition,
   PICS defines the following new form for referencing
   Internet Relay Chat (IRC) rooms:
   <B>URL :: </B>... | 'irc://' <I>host</I> '/' <I>alphanumpm</I>
       (where <I>host</I> is the usual Internet hostname)
<B>transmit-name-char ::</B> <I>alphanumpm</I> | '.' | '$' | ',' | ';' | ':'
                | '&amp;' | '=' | '?' | '!' | '*' | '~' | '@'
                | '#' | '_' | '%' <I>hex hex</I>
    <I>Note</I>: Use the "%" escape technique (% followed by the two
          hex digits that represent the character in the ASCII character
          set) to insert single or double quotation marks or parentheses.
<B>alphanumpm ::</B> 'A' | ... | 'Z' | 'a' | ... | 'z' | '0' | ... | '9' | <I>sign</I>
<B>sign ::</B> '+' | '-'
</PRE>
<P>
For reference, the following attributes are currently defined by the above
BNF:
<OL>
  <LI>
    Within a rating service, there are the attributes <B>category</B>,
    <B>default</B>, <B>description</B>, <B>extension</B>, <B>icon</B>,
    <B>name</B>, <B>PICS-version</B>, <B>rating-service</B>, and
    <B>rating-system</B>.
  <LI>
    Within a category, there are the attributes <B>description</B>,
    <B>extension</B>, <B>icon</B>,<B> integer</B>,<B> label</B>,<B>
    label-only</B>,<B> max</B>,<B> min</B>,<B> multivalue</B>, <B>name</B>,
    <B>transmit-as</B>, and <B>unordered</B>.
  <LI>
    Within a named value (an <B>enum</B> in the BNF syntax), there are the attributes
    <B>description</B>, <B>icon</B>, <B>name</B> and<B> value</B>.
  <LI>
    The defaultable attributes are those which can be overridden by a lexically
    enclosed description: <B>extension</B>, <B>integer</B>, <B>label-only</B>,
    <B>max</B>, <B>min</B>, <B>multivalue</B>, <B>unordered</B>. While it isn't
    actually possible to override an <B>extension</B>, careful design of extensions
    allows an equivalent facility.
</OL>
<H2>
  <A NAME="Semantics">Semantics of the <TT>application/pics-service</TT>
  Description</A>
</H2>
<P>
Recall that the MIME type <TT>application/pics-service</TT> is intended to
describe a particular rating service in sufficient detail to automatically
generate a user interface for configuring content selection software that
relies on the rating service.
<P>
The <I>quoted-URL</I> in the <I>rating-service</I> identifies the service.
This identifier is included in all the labels provided by the rating service.
Dereferencing the URL yields a human-readable description of the service.
If the optional URL for an icon for the rating service is supplied, it is
dereferenced relative to the rating service URL. The <I>name</I> of the rating
system is intended to be short and human-readable, with the
<I>description</I> being a longer description (suitable, perhaps, for a pop-up
box). A complete human-readable description is available from the rating
service's URL.
<P>
The <I>quoted-URL</I> in the <I>rating-system</I> identifies the rating system
used by this service. Dereferencing the URL yields a human-readable description
of the rating system. All remaining relative URLs in the
<TT>application/pics-service</TT> description are dereferenced relative to
the <I>rating-system</I> URL, since they describe features of the rating
system. The only exception is the rating service's icon, as described above,
which is dereferenced relative to the <I>rating-service</I> URL, so that
the service can maintain its own (possibly copyrighted) identity even if
it chooses to share a rating system with other services.
<P>
The machine-readable description also describes the categories used in the
rating system. There may be one or more categories for a given rating system.
A single document may have a rating on any or all of these categories. Categories
can be nested within one another.
<P>
A category has a "transmission name" which is used in the actual label for
a document. Transmission names should be as short as reasonable, but they
may be complete URLs if desired. They must be unique within a given rating
system (i.e. two categories in the same rating system must <I>not</I> have
the same transmission name; but see below for creating transmissions names
from nested categories.) Unlike the name and description strings, transmission
names are language-independent. That is, if a rating system is offered in
several languages, the transmission names must be the same in all of them.
Transmission names <EM>are</EM> case sensitive (to allow URLs to be used
as transmission names). In addition to the transmission name, which is required,
a category may optionally have an icon and a human-readable description.
<P>
Categories may be nested within one another (as in the case of <TT>color
</TT>in the example rating system). In this case, the transmission name is
created in the usual way by starting with the outermost category's
<B>transmit-as</B> string, adding a "/" and proceeding inward in the nesting.
Thus, the example rating system has three categories, and their transmission
names are <TT>color</TT>, <TT>color/hue</TT>, and <TT>color/intensity</TT>.
In order to simplify the user interface of configuration software, it is
wise to have few categories at any level of nesting; we recommend 10 or fewer.
<P>
Icons, if provided, may be of any size. We recommend, however, that icons
be as small as possible, since selection software is likely to embed them
in displays that include other text and images as well. We also recommend
that a rating service's category icons all be the same size.
<P>
Values in PICS labels may be integers or fractions with no greater range
or precision than that provided by IEEE single-precision floating point numbers.
Values may be given names by using the <B>label</B> attribute. When a value
is given a name, it may optionally have attached an icon and a human-readable
description. The description for each category can specify restrictions on
the range of permissible values for certain named attributes. Values may
be restricted in a variety of ways:
<OL>
  <LI>
    minimum (<B>min</B> attribute, defaults to <B>-INF</B>) value;
  <LI>
    maximum (<B>max</B> attribute, defaults to <B>+INF</B>) value;
  <LI>
    integer values only (<B>integer</B> attribute, defaults to <B>false</B> if
    the attribute is omitted, but <B>true</B> if it is present with no value
    specified);
  <LI>
    named values only (<B>label-only</B> attribute, defaults to <B>false</B>
    if the attribute is omitted, but <B>true</B> if it is present with no value
    specified).
  <LI>
    more than a single rating allowed for a given document (consider the dimension
    "sizes available"). This is indicated by setting the attribute
    <B>multivalue</B> to <B>true </B>(default is <B>false</B> if the attribute
    is omitted, but <B>true</B> if it is present with no value specified).
  <LI>
    unordered values (<B>unordered</B> attribute, defaults to <B>false</B> if
    the attribute is omitted, but <B>true</B> if its is present with no value
    specified.)
</OL>
<P>
For rating systems that contain large numbers of categories or deeply nested
categories, it is convenient to allow for inheritance of some attribute values.
In particular, the <B>defaultable-option</B>s of a category
(<B>extension</B>, <B>integer</B>, <B>label-only</B>, <B>max</B>, <B>min</B>,
<B>multivalue</B>, and <B>unordered</B>) are inherited by each category from
its enclosing (parent) category. These attributes can be given default values
for the entire rating service by using the <B>default</B> attributes. This
corresponds to value inheritance in object-oriented systems or lexical scoping
in programming languages. (Notice that not all attributes can be inherited.
<B>Rationale:</B> the set was chosen to include only those attributes that
can be overridden. Thus, the <B>enum-list</B> is not inheritable because
there is no way to say "don't give this value a name," which would be required
to override an inherited name.)
<P>
<B>Note:</B> While it would be nice to restrict the numeric values of ratings
to integers, the following examples motivate our decision to permit fractional
values.
<OL>
  <LI>
    The MPAA rating system was changed to interpolate a new category (PG-13)
    between "PG" and "R". Had their system been encoded with a tightly packed
    integer scale (e.g., G=1, PG=2, R=3) it would have required rescinding many
    existing labels when the change occurred. With fractional numbers there is
    no need to renumber (e.g., PG-13 could be associated with the fraction 2.5).
  <LI>
    It may be desirable to include the cost of an item in a content label. This
    cost may not be an integral number of currency units (think, for example,
    of a micropayment system in which charges of small fractions of a cent are
    permitted).
  <LI>
    Ratings may be generated by statistical means from the responses of many
    people. Such ratings could be rounded off to an integer before presentation,
    but this loses much important information.
</OL>
<H2>
  <A NAME="Glossary">Glossary </A>
</H2>
<DL COMPACT>
  <DT>
    application/pics-service
  <DD>
    A new MIME data type, defined in this document.
  <DT>
    application/pics-labels
  <DD>
    A new MIME data type used to transmit one or more <I>labels</I>, defined
    in <A href="http://w3.org/PICS/labels.html">PICS Labels</A>.
  <DT>
    BNF
  <DD>
    Backus-Naur Form (or Backus Normal Form). A notation for describing a formal
    syntax, used extensively in describing programming languages and
    computer-readable data formats.
  <DT>
    category
  <DD>
    The part of a rating system which describes a particular criterion used for
    rating. For example, a rating system might have three categories named "sexual
    material," "violence," and "vocabulary." Also called a <I>dimension</I>.
  <DT>
    content label
  <DD>
    A data structure containing information about a given document's contents.
    Also called a <I>rating</I> or <I>content rating</I>. The content label may
    accompany the document it is about or be available separately.
  <DT>
    content rating
  <DD>
    See <I>content label</I>.
  <DT>
    dimension
  <DD>
    See <I>category</I>.
  <DT>
    HTML
  <DD>
    HyperText Markup Language. A means of representing <I>hypertext</I> documents.
    Based on <I>SGML</I>. See the
    <A HREF="http://ds.internic.net/rfc/rfc1866.txt">HTML 2.0 Proposed
    Standard</A>.
  <DT>
    HTTP
  <DD>
    HyperText Transfer Protocol. Used for retrieving document contents and/or
    descriptive header information. See the
    <A href="http://w3.org/pub/WWW/Protocols/HTTP1.0/draft-ietf-http-spec.html">draft
    HTTP specification</A>.
  <DT>
    hypertext
  <DD>
    Text, graphics, and other media connected through links.
  <DT>
    MIME
  <DD>
    Multimedia Internet Message Extension. A technique for sending arbitrary
    data through electronic mail on the Internet. See
    <A href="ftp://ds.internic.net/rfc/rfc1521.txt">RFC-1521</A>
  <DT>
    PICS
  <DD>
    <A href="http://w3.org/PICS">Platform for Internet Content Selection</A>,
    the name for both the suite of specification documents of which this is a
    part, and for the organization writing the documents.
  <DT>
    rating
  <DD>
    See <I>content label</I>.
  <DT>
    label bureau
  <DD>
    A computer system which supplies, via a computer network, ratings of documents.
    It may or may not provide the documents themselves.
  <DT>
    rating server
  <DD>
    See <I>label bureau</I>.
  <DT>
    rating service
  <DD>
    An individual or organization that assigns labels according to some rating
    system, and then distributes them, perhaps via a label bureau or via CD-ROM.
  <DT>
    rating system
  <DD>
    A method for rating information. A rating system consists of one or more
    <I>categories</I>.
  <DT>
    scale
  <DD>
    The range of permissible values for a category.
  <DT>
    SGML
  <DD>
    Standard Generalized Markup Language. See
    <A href="http://www.iso.ch/cate/d16387.html">ISO 8879</A>.
  <DT>
    transmission name
  <DD>
    (of a <I>category</I>) The short name intended for use over a network to
    refer to the category. This is distinct from the category name in as much
    as the transmission name must be language-independent, encoded in ASCII,
    and as short as reasonably possible. Within a single <I>rating system</I>
    the transmission names of all categories must be distinct.
  <DT>
    URL
  <DD>
    Uniform Resource Locator. Described in
    <A HREF="ftp://ds.internic.net/rfc/rfc1738.txt">RFC-1738</A>. A URL describes
    the location and means of retrieval for a single document. It consists of
    three components: the "scheme" (protocol used to retrieve a document, like
    "http" or "ftp"), a host name, and a hierarchical document name within that
    host. For example "http://w3.org/PICS" is the URL of the PICS home page.
    The scheme for retrieving it is "http," the host is "w3.org" and the name
    within that host is "PICS". Notice that PICS defines an additional scheme
    beyond those listed in RFC-1738, described in
    <A href="http://w3.org/PICS/services.html">Rating Services and Rating
    Systems</A>, which allows Chat (IRC) rooms to be named.
  <DT>
    UTF-7
  <DD>
    An <A href="ftp://ds.internic.net/rfc/rfc1642.txt">encoding technique</A>
    that can be used to transmit Unicode over 7-bit ASCII transport systems such
    as Internet electronic mail.
</DL>
<H2>
  <A NAME="References">References</A>
</H2>
<OL>
  <LI>
    PICS, <A href="http://w3.org/PICS/labels.html">"Label Syntax and Communication
    Protocols"</A>, Internet Draft, "draft-pics-labels-00.txt", 11/21/95.
  <LI>
    T. Berners-Lee, D. Connolly, "Hypertext Markup Language - 2.0",
    <A href="ftp://ds.internic.net/rfc/rfc1866.txt">RFC 1866</A>, 11/03/1995.
  <LI>
    N. Borenstein, N. Freed, "MIME (Multipurpose Internet Mail Extensions) Part
    One: Mechanisms for Specifying and Describing the Format of Internet Message
    Bodies", <A href="ftp://ds.internic.net/rfc/rfc1521.txt">RFC 1521</A>,
    09/23/1993.
  <LI>
    T. Berners-Lee, L. Masinter, M. McCahill, "Uniform Resource Locators (URLs)",
    <A href="ftp://ds.internic.net/rfc/rfc1738.txt">RFC 1738</A>, 12/20/94.
  <LI>
    D. Goldsmith, M. Davis, "UTF-7 - A Mail-Safe Transformation Format of Unicode",
    <A href="ftp://ds.internic.net/rfc/rfc1642.txt">RFC 1642</A>, 7/13/94.
</OL>
<H2>
  <A NAME="Acknowledgments">Acknowledgments</A>
</H2>
<P>
Comments and suggestions from the following people are gratefully acknowledged:
<PRE>
Brenda Baker, Lucent
Scott Berkun, Microsoft
Tim Berners-Lee, W3C
Roxana Bradescu, AT&amp;T
Daniel W. Connolly, W3C
Roy Fielding, W3C
Jay Friedland, SurfWatch
Henrik Frystyk Nielsen, W3C
Wayne Gramlich, Sun
Woodson Hobbs, NewView
Rohit Khare, W3C
Charlie Kim, Apple
John C. Klensin, MCI
Tim Krauskopf, Spyglass
Breen Liblong, IFSI
Ann McCurdy, Microsoft
Rich Petke, CompuServe
Eric Prud'hommeaux, W3C
Dave Raggett, W3C
Bob Schloss, IBM
Ray Soular, SafeSurf
Jason Thomas, MIT
G. Winfield Treese, OpenMarket
Richard Wolpert, Providence Systems
</PRE>
<H2>
  <A NAME="Appendix A">Appendix A: The Ages Rating Service</A>
</H2>
<P>
One of the simplest possible rating systems uses a single category, "Minimum
recommended age." We present the machine description for a fictional service
that uses this rating system.
<PRE>
((PICS-version 1.1)
 (rating-system "http://www.ages.org/our-system/")
 (rating-service "http://www.ages.org/our-service/v1.0/")
 (name "The Ages Rating Service")
 (description "We estimate the maturity required to view materials on
the Internet.")
 (category (transmit-as "age") (name "Minimum Recommended Age") (integer true)))
</PRE>
<H2>
  <A NAME="Appendix B">Appendix B: RSAC Rating Service</A>
</H2>
<P>
As a specific example of a deployed rating service encoded using the PICS
machine-readable description format, we present the service supplied by the
Recreational Software Advisory Council (RSAC). They use their own (copyrighted)
rating system, which we include with their permission. The rating system
contains four categories: Violence, Nudity, Sex, and Language. Each category
is rated on a scale from 0 to 4, with a specific description for each value.
Only values with names are permitted.
<PRE>
((PICS-version 1.1)
 (rating-system "http://www.rsac.org/ratingsv01.html")
 (rating-service "http://www.rsac.org/")
 (name "The RSAC Ratings Service")
 (description "The Recreational Software Advisory Council rating
service.  Based on the work of Dr. Donald F. Roberts of Stanford
University, who has studied the effects of media on children for
nearly 20 years.")
 (default (label-only true))

 (category
  (transmit-as "v")
  (name "Violence")
  (label
   (name "Conflict")
   (description "Harmless conflict; some damage to objects")
   (value 0))
  (label
   (name "Fighting")
   (description "Creatures injured or killed; damage to objects;
fighting")
   (value 1))
  (label
   (name "Killing")
   (description "Humans injured or killed with small amount of blood")
   (value 2))
  (label
   (name "Blood and Gore")
   (description "Humans injured or killed; blood and gore")
   (value 3))
  (label
   (name "Wanton Violence")
   (description "Wanton and gratuitous violence; torture; rape")
   (value 4)))

 (category
  (transmit-as "s")
  (name "Sex")
  (label
   (name "None")
   (description "Romance; no sex")
   (value 0))
  (label
   (name "Passionate kissing")
   (description "Passionate kissing")
   (value 1))
  (label
   (name "Clothed sexual touching")
   (description "Clothed sexual touching")
   (value 2))
  (label
   (name "Non-explicit sexual activity")
   (description "Non-explicit sexual activity")
   (value 3))
  (label
   (name "Explicit sexual activity; sex crimes")
   (description
    "Explicit sexual activity; sex crimes")
   (value 4)))

 (category
  (transmit-as "n")
  (name "Nudity")
  (label
   (name "None")
   (description "No nudity or revealing attire")
   (value 0))
  (label
   (name "Revealing Attire")
   (description "Revealing attire")
   (value 1))
  (label
   (name "Partial Nudity")
   (description "Partial nudit")
   (value 2))
  (label
   (name "Frontal Nudity")
   (description "Non-sexual frontal nudity")
   (value 3))
  (label
   (name "Explicit")
   (description
    "Provocative frontal nudity")
   (value 4)))

 (category
  (transmit-as "l")
  (description "Language")
  (label (name "Slang")
         (description "Inoffensive slang; no profanity")
         (value 0))
  (label (name "Mild Expletives")
         (description "Mild expletives")
         (value 1))
  (label (name "Expletives")
         (description "Expletives; non-sexual anatomical references")
         (value 2))
  (label (name "Obscene Gestures")
         (description "Strong, vulgar language; obscene gestures")
         (value 3))
  (label (name "Explicit")
         (description "Crude or explicit sexual references")
         (value 4))))
</PRE>
<H2>
  <A NAME="Appendix C">Appendix C: The SafeSurf~~ Rating Service</A>
</H2>
<P>
SafeSurf, a parents' organization, has established a rating system that is
used for self-rating by a large and growing number of sites on the Internet.
They have provided a machine-readable version of their service to PICS as
a demonstration of a more complex rating system that includes sub-categories
as well as a document classification system. The following specification
includes a full description of the rating part of the SafeSurf system, with
only a small stub to represent the classifications.
<PRE>
((PICS-version 1.1)
 (rating-system "http://www.classify.org/safesurf/")
 (rating-service "http://www.classify.org/safesurf/service/")
 (name "SafeSurf Rating Service")
 (description "The SafeSurf SS~~ Rating and Classification Standard.  Designed with input from thousands of parents and Net citizens worldwide to specifically to handle the vast potential of the Internet, it empowers each family to make informed decisions concerning accessibility of online content. Copyright 1995.  All Rights Reserved.")

 (category (transmit-as "SS~~000") (name "Age Range")
   (label
     (name "All Ages")
     (value 1))
   (label
     (name "Older Children")
     (value 2))
   (label
     (name "Younger Teens")
     (value 3))
   (label
     (name "Older Teens")
     (value 4))
   (label
     (name "Adult Supervision Recommended")
     (value 5))
   (label
     (name "Adults")
     (value 6))
   (label
     (name "Limited to Adults")
     (value 7))
   (label
     (name "Adults Only")
     (value 8))
   (label
     (name "Explicitly for Adults")
     (value 9)))

 (category (transmit-as "SS~~001") (name "Profanity")
   (label
     (name "Subtle Innuendo")
     (description "Subtly Implied through the use of Slang")
     (value 1))
   (label
     (name "Strong Innuendo")
     (description "Expressly implied through the use of Slang")
     (value 2))
   (label
     (name "Technical Reference")
     (description "Dictionary, encyclopedic, news, technical references") (value 3))
   (label
     (name "Non-Graphic-Artistic")
     (description "Limited non-sexual expletives used in a artistic fashion") (value 4))
   (label
     (name "Graphic-Artistic")
     (description "Non-sexual expletives used in a artistic fashion") (value 5))
   (label
     (name "Graphic")
     (description "Limited use of expletives and obscene gestures") (value 6))
   (label
     (name "Detailed Graphic")
     (description "Casual use of expletives and obscene gestures") (value 7))
   (label
     (name "Explicit Vulgarity")
     (description "Heavy use of vulgar language and obscene gestures. Unsupervised Chat Rooms.")
     (value 8))
   (label
     (name "Explicit and Crude")
     (description "Saturated with crude sexual references and gestures. Unsupervised Chat Rooms.")
     (value 9)))

 (category (transmit-as "SS~~002") (name "Heterosexual Themes")
    (label
      (name "Subtle Innuendo")
      (description "Subtly Implied through the use of metaphor")
      (value 1))
    (label
      (name "Strong Innuendo")
      (description "Explicitly implied (not described) through the use of metaphor")
      (value 2))
    (label
      (name "Technical Reference")
      (description "Dictionary, encyclopedic, news, medical references")
      (value 3))
    (label
      (name "Non-Graphic-Artistic")
      (description "Limited metaphoric descriptions used in a artistic fashion")
      (value 4))
    (label (name "Graphic-Artistic")
      (description "Metaphoric descriptions used in a artistic fashion")
      (value 5))
    (label
      (name "Graphic")
      (description "Descriptions of intimate sexual acts")
      (value 6))
    (label
      (name "Detailed Graphic")
      (description "Descriptions of intimate details of sexual acts")
      (value 7))
    (label
      (name "Explicit Vulgarity")
      (description "Explicit Descriptions of intimate details of sexual acts designed to arouse. Inviting interactive sexual participation. Unsupervised Sexual Chat Rooms or Newsgroups")
      (value 8))
    (label
      (name "Explicit and Crude")
      (description "Profane Graphic Descriptions of intimate details of sexual acts designed to arouse. Inviting interactive sexual participation.  Unsupervised Sexual Chat Rooms or Newsgroups")
      (value 9)))

 (category (transmit-as "SS~~003") (name "Homosexual Themes")
    (label
      (name "Subtle Innuendo")
      (description "Subtly Implied through the use of metaphor")
      (value 1))
    (label
      (name "Strong Innuendo")
      (description "Explicitly implied (not described) through the use of metaphor")
      (value 2))
    (label
      (name "Technical Reference")
      (description "Dictionary, encyclopedic, news, medical references")
      (value 3))
    (label
      (name "Non-Graphic-Artistic")
      (description "Limited metaphoric descriptions used in a artistic fashion")
      (value 4))
    (label
      (name "Graphic-Artistic")
      (description "Metaphoric descriptions used in a artistic fashion")
      (value 5))
    (label
      (name "Graphic")
      (description "Descriptions of intimate sexual acts")
      (value 6))
    (label
      (name "Detailed Graphic")
      (description "Descriptions of intimate details of sexual acts")
      (value 7))
    (label
      (name "Explicit Vulgarity")
      (description "Explicit Descriptions of intimate details of sexual acts designed to arouse. Inviting interactive sexual participation. Unsupervised Sexual Chat Rooms or Newsgroups")
      (value 8))
    (label
      (name "Explicit and Crude")
      (description "Profane Graphic Descriptions of intimate details of sexual acts designed to arouse. Inviting interactive sexual participation.  Unsupervised Sexual Chat Rooms or Newsgroups")
      (value 9)))


 (category (transmit-as "SS~~004") (name "Nudity")
    (label
      (name "Subtle Innuendo")
      (description "Subtly Implied through the use of composition, lighting, shaping, revealing clothing, etc.")
      (value 1))
    (label
      (name "Strong Innuendo")
      (description "Explicitly implied (not shown) through the use of composition, lighting, shaping or revealing clothing")
      (value 2))
    (label
      (name "Technical Reference")
      (description "Dictionary, encyclopedic, news, medical references")
      (value 3))
    (label
      (name "Non-Graphic-Artistic")
      (description "Classic works of art presented in public museums for family viewing")
      (value 4))
    (label
      (name "Graphic-Artistic")
      (description "Artistically presented without full frontal nudity")
      (value 5))
    (label
      (name "Graphic")
      (description "Artistically presented with frontal nudity")
      (value 6))
    (label
     (name "Detailed Graphic")
     (description "Erotic frontal nudity")
      (value 7))
    (label
      (name "Explicit Vulgarity")
      (description "Detailed provocative presentation")
      (value 8))
    (label
      (name "Explicit and Crude")
      (description "Explicit pornographic presentation")
      (value 9)))

 (category (transmit-as "SS~~005")
    (name "Violence")
    (label
      (name "Subtle Innuendo")
      (value 1))
    (label
      (name "Strong Innuendo")
      (value 2))
    (label
      (name "Technical Reference")
      (value 3))
    (label
      (name "Non-Graphic-Artistic")
      (value 4))
    (label
      (name "Graphic-Artistic")
      (value 5))
    (label
      (name "Graphic")
      (value 6))
    (label
      (name "Detailed Graphic")
      (value 7))
    (label
      (name "Inviting Participation in Graphic Interactive Format")
      (value 8))
    (label
      (name "Encouraging Personal Participation, Weapon Making")
      (value 9)))

 (category (transmit-as "SS~~006")
   (name "Sex Violence and Profanity")
    (label
      (name "Subtle Innuendo")
      (value 1))
    (label
      (name "Strong Innuendo")
      (value 2))
    (label
      (name "Technical Reference")
      (value 3))
    (label
      (name "Non-Graphic-Artistic")
      (value 4))
    (label
      (name "Graphic-Artistic")
      (value 5))
    (label
      (name "Graphic")
      (value 6))
    (label
      (name "Detailed Graphic")
      (value 7))
    (label
      (name "Explicit Vulgarity")
      (value 8))
    (label
      (name "Explicit and Crude")
      (value 9)))

 (category (transmit-as "SS~~007")
   (name "Intolerance of another person's racial, religious, or gender backround")
    (label
      (name "Subtle Innuendo")
      (value 1))
    (label
      (name "Strong Innuendo")
      (value 2))
    (label
      (name "Technical Reference")
      (value 3))
    (label
      (name "Non-Graphic-Literary")
      (value 4))
    (label
      (name "Graphic-Literary")
      (value 5))
    (label
      (name "Graphic Discussions")
      (value 6))
    (label
      (name "Endorsing Hatred")
      (value 7))
    (label
      (name "Endorsing Violent or Hateful Action")
      (value 8))
    (label
      (name "Advocating Violent or Hateful Action")
      (value 9)))

 (category (transmit-as "SS~~008") (name "Glorifying Drug Use")
    (label
      (name "Subtle Innuendo")
      (value 1))
    (label
      (name "Strong Innuendo")
      (value 2))
    (label
      (name "Technical Reference")
      (value 3))
    (label
      (name "Non-Graphic-Artistic")
      (value 4))
    (label
      (name "Graphic-Artistic")
      (value 5))
    (label
      (name "Graphic")
      (value 6))
    (label
      (name "Detailed Graphic")
      (value 7))
    (label
      (name "Simulated Interactive Participation")
      (value 8))
    (label
      (name "Soliciting Personal Participation")
      (value 9)))

 (category (transmit-as "SS~~009") (name "Other Adult Themes")
    (label
      (name "Subtle Innuendo")
      (value 1))
    (label
      (name "Strong Innuendo")
      (value 2))
    (label
      (name "Technical Reference")
      (value 3))
    (label
      (name "Non-Graphic-Artistic")
      (value 4))
    (label
      (name "Graphic-Artistic")
      (value 5))
    (label
      (name "Graphic")
      (value 6))
    (label
      (name "Detailed Graphic")
      (value 7))
    (label
      (name "Explicit Vulgarity")
      (value 8))
    (label
      (name "Explicit and Crude")
      (value 9)))

 (category (transmit-as "SS~~00A") (name "Gambling")
    (label
      (name "Subtle Innuendo")
      (value 1))
    (label
      (name "Strong Innuendo")
      (value 2))
    (label
      (name "Technical Discussion")
      (value 3))
    (label
      (name "Non-Graphic-Artistic, Advertising")
      (value 4))
    (label
      (name "Graphic-Artistic, Advertising")
      (value 5))
    (label
      (name "Simulated Gambling")
      (value 6))
    (label
      (name "Real Life Gambling without Stakes")
      (value 7))
    (label
      (name "Encouraging Interactive Real Life Participation with Stakes")
      (value 8))
    (label
      (name "Providing Means with Stakes")
      (value 9)))

 (category (transmit-as "SS~~100")  (name "General Information")
      (min 1) (max 100) (integer true)))

<P>
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<ADDRESS><A HREF="mailto:web-human@w3.org">Webmaster</A><BR>$Date: 2009/11/24 18:23:30 $
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