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<h1>Protocol for Web Description Resources (POWDER): Primer</h1>

<h2>W3C Working Group Note 1 September 2009</h2>
<dl>
  <dt>This version:</dt>
  <dd><a href="http://www.w3.org/TR/2009/NOTE-powder-primer-20090901/">http://www.w3.org/TR/2009/NOTE-powder-primer-20090901/</a></dd>
  <dt>Latest version:</dt>
    <dd><a
      href="http://www.w3.org/TR/powder-primer/">http://www.w3.org/TR/powder-primer/</a></dd>
  <dt>Previous version</dt>
  <dd><a href="http://www.w3.org/TR/2009/NOTE-powder-primer-20090604/">http://www.w3.org/TR/2009/NOTE-powder-primer-20090604/</a></dd>
  <dt>Editor:</dt>
    <dd>Kai Scheppe, Deutsche Telekom AG</dd>
</dl>

<p class="copyright"><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a>
&copy; 2009 <a href="http://www.w3.org/"><acronym
title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><acronym
title="Massachusetts Institute of Technology">MIT</acronym></a>, <a
href="http://www.ercim.org/"><acronym
title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>,
<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply. </p>
<hr />
</div>

<h2 class="notoc">Abstract</h2>

<p>POWDER &mdash; the Protocol for Web Description Resources &mdash; provides
a mechanism to describe and discover Web resources and helps the users to
make a decision whether a given resource is of interest. There are a variety
of use cases: from providing a better means to describing Web resources and
creating trustmarks to aiding content discovery, child protection and
Semantic Web searches.</p>

<p>There are two varieties of POWDER: a complex, semantically rich variety,
called POWDER-S, and a much simpler version, just called POWDER, which is
intended as the primary transport mechanism for Description Resources.
POWDER-S can be generated automatically from POWDER.</p>
<!-- ABSTRACT -->
<hr />
<!-- SOTD -->

<h2>Status of this Document</h2>

<p><em>This section describes the status of this document at the time of its
publication. Other documents may supersede this document. A list of current
W3C publications and the latest revision of this technical report can be
found in the <a href="http://www.w3.org/TR/">W3C technical reports index</a>
at http://www.w3.org/TR/.</em></p>


<p>This is the fourth publication of the document as a Working Group Note by the
<a href="http://www.w3.org/2007/powder/">POWDER Working Group</a> which does not expect to publish further versions.
There have been no changes since the <a href="http://www.w3.org/TR/2009/NOTE-powder-test-20090403/">previous version</a>.</p>

<p>Publication of this Note is synchronized with several other documents:</p>
<ul>
  <li><a href="http://www.w3.org/TR/2009/REC-powder-dr-20090901/">POWDER: Description Resources</a> (Recommendation)</li>
  <li><a href="http://www.w3.org/TR/2009/REC-powder-grouping-20090901/">POWDER: Grouping of Resources</a> (Recommendation)</li>
  <li><a href="http://www.w3.org/TR/2009/REC-powder-formal-20090901/">POWDER: Formal Semantics</a> (Recommendation)</li>
  <li><a href="http://www.w3.org/TR/2009/NOTE-powder-test-20090604/">POWDER: Test Suite</a> (Working Group Note)</li>
</ul>

  <p>To send comments, please use the
  public mailing list (<a href="mailto:public-powderwg@w3.org">public-powderwg@w3.org</a>), an <a href="http://lists.w3.org/Archives/Public/public-powderwg/">archived
  mailing list</a>. See <a href="http://www.w3.org/Mail/">W3C mailing list and archive usage guidelines</a>.</p>

<p>Publication as a Working Group Note does not imply endorsement by the W3C Membership. This is
a draft document and may be updated, replaced or obsoleted by other documents at any time. It is
inappropriate to cite this document as other than work in progress.</p>

  <p>This document has been produced as part of the <a href=
  "http://www.w3.org/2001/sw/">Semantic Web Activity</a>, following the procedures set out for the <a href="http://www.w3.org/Consortium/Process/">W3C Process</a>.</p>
<p> This document was produced by a group operating under the <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent Policy</a>. W3C maintains a <a rel="disclosure" href="http://www.w3.org/2004/01/pp-impl/40243/status">public list of any patent disclosures</a> made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the W3C Patent Policy</a>. </p>

<hr />
<!-- CONTENTS -->

<h2 id="ToC">Table of Contents</h2>
<ol>
  <li><a href="#What">What is POWDER?</a></li>
  <li><a href="#would">Why would I want to use POWDER?</a>
    <ul>
      <li><a href="#Grouping">Grouping</a></li>
      <li><a href="#Data">Data retrieval efficiency</a></li>
      <li><a href="#Profile">Profile matching</a></li>
      <li><a href="#Trustmarks">Trustmarks</a></li>
      <li><a href="#Semantic">Semantic Annotation</a></li>
      <!-- <li><a href="#richmeta">Rich Meta Data</a> </li> -->
    </ul>
  </li>
  <li><a href="#does">How does POWDER work in the real world?</a>
    <ul>
      <li><a href="#Trustmarks2">Trustmarks</a>
        <ul>
          <li><a href="#VISUAL">Visual notification</a></li>
          <li><a href="#MONITORING">Monitoring</a></li>
          <li><a href="#Descriptio">Description authentication</a> </li>
        </ul>
      </li>
      <li><a href="#Accessibil">Accessibility</a></li>
      <li><a href="#MobileOK">MobileOK</a></li>
      <li><a href="#Child">Child Protection</a></li>
      <li><a href="#Functional">Functional User Experience</a></li>
      <li><a href="#Privileged">Privileged Content</a></li>
      <li><a href="#Semantics">Semantics</a>
        <ul>
          <li><a href="#Search">Search</a></li>
          <li><a href="#Distinguis">Distinguishing opinion</a></li>
        </ul>
      </li>
    </ul>
  </li>
  <li><a href="#POWDER">How do I use POWDER?</a>
    <ul>
      <li><a href="#create">How do I create a Description Resource?</a></li>
      <li><a href="#publish">How do I publish a DR?</a></li>
      <li><a href="#ensuretrust">How do I make my DR more
      trustworthy?</a></li>
      <li><a href="#find">How do I find DRs for a document?</a></li>
      <li><a href="#process-docs">How do I process POWDER documents?</a></li>
      <li><a href="#process1">How do I process POWDER-S?</a></li>
    </ul>
  </li>
  <li><a href="#What1">What do I need to use POWDER?</a> </li>
  <li><a href="#powder-s">POWDER-S</a></li>
  <li><a href="#examples">Examples</a>
    <ul>
      <li><a href="#ICRA1">ICRA Labelling</a></li>
      <li><a href="#example_mobileOK">mobileOK</a></li>
    </ul>
  </li>
  <li><a href="#Acknowledg">Acknowledgements</a> </li>
  <li><a href="#References">References</a> </li>
</ol>
<hr />
<!-- What is it? -->

<h2><a name="What" id="What">1. What is POWDER?</a></h2>

<p>POWDER is an abbreviation for "Protocol for Web Description Resources."
The goal of the working group has been to develop a mechanism that allows not
only the provision of descriptions but also a way to apply them to groups of
online resources and for the authentication of those descriptions.</p>

<p>The primary 'unit of information' within POWDER is the <strong>Description
Resource</strong> (DR), which comprises:</p>
<ul>
  <li>attribution (assertions about both the circumstances of its own
    creation and the entity that created it);</li>
  <li>scope (to which resources does the description apply);</li>
  <li>the description itself.</li>
</ul>

<p>There are two varieties of POWDER:</p>
<ul>
  <li>a simple version, called POWDER;</li>
  <li>a semantically rich variety, called POWDER-S.</li>
</ul>

<p>The simple version has relatively loose, human-readable 'operational
semantics,' and is written in XML.</p>

<p>The semantically-rich version, known as POWDER-S, allows POWDER to harness
the Semantic Web at large and encodes formal semantics that underpin the
operational semantics. </p>

<p>There is a third, transitory version of POWDER, called POWDER-BASE, which
is intended for processors and is not of concern for this document. A
"Gleaning Resource Descriptions from Dialects of Languages" (<a
href="http://www.w3.org/TR/grddl/">GRDDL)</a> transform, may automatically
generate POWDER-S as RDF/OWL from a POWDER document. The details of this
transformation are defined in the [<a href="#formal">FORMAL</a>] document.
XSLTs are available to support this. Alternatively, POWDER-S may be written
directly.</p>

<p>There is no restriction on which form to use, but it should be noted that
the simple version is intended as the primary exchange mechanism between
systems. All POWDER tools should process POWDER. Using the POWDER-S form is
optional, so that a processor may not necessarily understand this form.</p>

<p>POWDER-S is designed to facilitate incorporation of POWDER information in
larger RDF-based systems and it should be noted that such systems will need
to implement a Semantic Extension to do this (see <a href="#process1">How do
I process POWDER-S</a>).</p>

<p>Importantly, POWDER allows a variety of questions to be answered about a
given Web resource or group of resources, without having to actually retrieve
and inspect the resource(s).</p>

<p>At first a Description Resource is simply a claim: somebody is making some
statement about a given resource, or group of resources. However, most users
would have to trust the person that made the claim before deciding whether to
trust the data. If a DR is made available directly by a well-known content
provider that is trusted to uphold a certain level of quality, then the data
might readily be trusted. However, this will not always be sufficient. Since
a DR may be published by anyone, anywhere, to describe anything, an end user
may reasonably want to query the cited author of the DR to ask questions such
as: Did you really make that claim? And, if so, when? Would you make the same
claim today?</p>

<p>For some situations this might still not be sufficient for the end user.
To facilitate the further extension of trust a means has been provided to
allow certification of DRs. A Description Resource that has been certified
immediately gains in trust, through the verification by a third and trusted
party of the original claims made by the DR author.</p>

<p>Through the combination of these tools various questions can be answered
using a Description Resource, without having to retrieve the resource
itself.</p>

<p>The following are examples of questions that could be asked using
POWDER:</p>
<ul>
  <li>Which resources does the DR describe?</li>
  <li>What is the description?</li>
  <li>Who has created the description?</li>
  <li>When was the description created?</li>
  <li>Until when is the description considered valid?</li>
  <li>From when is the description considered valid?</li>
  <li>Does anybody agree with this description?</li>
  <li>Do other descriptions exist about this group of resources?</li>
</ul>

<p>The POWDER Suite consists of the following documents, in order of
recommended reading </p>
<ol>
  <li><a href="http://www.w3.org/TR/powder-primer">POWDER: Primer</a> - this
    document.</li>
  <li><a href="http://www.w3.org/TR/powder-use-cases/">POWDER: Use Cases and
    Requirements</a> - the premises upon which POWDER was created.</li>
  <li><a href="http://www.w3.org/TR/powder-dr/">POWDER: Description
    Resources</a> - the definition and structure of Description Resources
    (DR).</li>
  <li><a href="http://www.w3.org/TR/powder-grouping/">POWDER: Grouping of
    Resources</a> - the method by which sets of resources may be defined to
    which DRs apply.</li>
  <li><a href="http://www.w3.org/TR/powder-formal/">POWDER: Formal
    Semantics</a> - a detailed description of the formal semantics of
    POWDER-S and of the GRDDL transformation process.</li>
  <li><a href="http://www.w3.org/TR/powder-test/">POWDER: Test Suite</a> -
    provides data against which conformant POWDER applications may be
  tested.</li>
  <li><a href="http://www.w3.org/TR/powder-voc/">POWDER: Web Description
    Resources (WDRS) POWDER-S Vocabulary</a> - the definition of the RDF
    vocabulary that is used to express POWDER-S.</li>
  <li><a href="http://www.w3.org/2007/05/powder">XML Schema for POWDER and
    POWDER-BASE</a> - the namespace document/schema for POWDER</li>
</ol>

<p>There are a variety of tools available to aid in the implementation of
POWDER.</p>
<ol>
  <li>POWDER Validator</li>
  <li>POWDER Processor - PERL based</li>
  <li>POWDER-S Processing kit</li>
  <li>POWDER Processor - PHP based</li>
  <li>TransOnto - a semantic POWDER Processor</li>
  <li>POWDER to POWDER-BASE transformation tool</li>
  <li>POWDER to POWDER-BASE XSLT (using XSLT2)</li>
  <li>POWDER-BASE to POWDER-S XSLT</li>
  <li>POWDER Grouping Tester</li>
</ol>
<p>Details and newest versions can be found at the <a
href="http://www.w3.org/2007/powder/">POWDER home page</a>. </p>

<h2><a name="would" id="would">2. Why would I want to use POWDER?</a></h2>

<p>The amount of information on the web grows continually. Conversely, the
amount of time people have to devote to this information seems to be
decreasing. To cope with these constraints (too much information and too
little time), users need a system where more customized content is delivered
to them in the most personalized way. Basically the average user wants to get
online, find what they want and move on.</p>

<p>From an End User's Perspective, POWDER:</p>
<ul>
  <li>delivers more of what you asked for and less of what you don't
  want;</li>
  <li>allows you to judge the trustworthiness of information found on the
  Web;</li>
  <li>brings the best of the Web to your browser.</li>
</ul>

<p>From a Publisher's Perspective, POWDER:</p>
<ul>
  <li>is an easy and inexpensive way to describe lots of things at once (such
    as everything on a Web site);</li>
  <li>is open to authentication so that others know they can trust your
  data;</li>
  <li>opens up your data to the Semantic Web, without having to know anything
    about RDF</li>
</ul>

<p>From a Service Provider's Perspective, POWDER:</p>
<ul>
  <li>supports real-time content personalization;</li>
  <li>makes discovering relevant &amp; trustworthy content easier;</li>
  <li>identifies online resources that meet criteria that are not solely
    based on popularity.</li>
</ul>

<p>Use Cases That Have Driven the Development of POWDER Include:</p>
<ul>
  <li>context-aware content discovery and delivery</li>
  <li>content personalization (e.g. for accessibility, delivery context,
    child protection)</li>
  <li>interoperable, machine-readable trustmarks</li>
</ul>

<p>POWDER offers a much more dependable means by which to deliver the most
relevant information without putting the onus on the user to verify and
validate every aspect. Both information providers and information consumers
are interested in getting the highest return for their individual investment
of time and effort.</p>


<h3><a name="Grouping" id="Grouping">Grouping</a></h3>

<p>This is one of the most powerful overarching features of POWDER and one
that has been an unresolved challenge until now. It allows one to offer
semantically rich information about entire groups of online resources with
both flexibility and precision in the way the group is defined. A processor
may use a single POWDER document to extract information about many - perhaps
huge numbers of - other resources. In addition, the maintenance of such
Description Resources is simplified by support for defining many descriptions
in a single document.</p>

<p>The methods for grouping resources range from the individual listing of
IRIs, through the specification of things like domain names and paths, to the
matching of IRIs against regular expressions. Requests made to a POWDER
Processor, however, are always handled at the level of an individual
resource. The RDF returned will be triples about that resource, allowing an
application to analyze the data and decide how to act case by case.</p>

<p>N.B. POWDER uses the term IRI (Internationalized Resource Identifier [<a
href="#iri">IRI</a>]). The more common term URI is a subset of IRIs, so that
all URIs are also IRIs.</p>

<h3><a name="Data" id="Data">Data retrieval efficiency</a></h3>

<p>Traditionally, meta information is always linked to a single resource and
is usually embedded within it, as is the case, for example, with the HTML
META element where the attributes are chosen and the values are given by the
author. When metadata is embedded in content in this way, the complete
resource has to be retrieved in full to then determine if it is of interest
or not.</p>

<p>POWDER describes online resources that may be of interest to a user or a
system. The keyword is "may", because the requester can decide prior to
resource retrieval whether the resource should be retrieved at all, based on
information provided by a Description Resource. This makes information
retrieval more efficient and precise by reducing network traffic and server
load. From a user perspective it means greater personalization and less
irrelevant content.</p>

<h3><a name="Profile" id="Profile">Profile matching</a></h3>

<p>POWDER allows profile matching - that is, the retrieval of resources
according to user preferences, device capabilities and current state at the
time of content delivery. The use cases [<a href="#usecases">USECASES</a>]
deal with adaptive search results based on context, suitability for mobile
devices, functional user experiences based on capabilities, web
accessibility, child protection and privileged content.</p>

<h3><a name="Trustmarks" id="Trustmarks">Trustmarks</a></h3>

<p>Resources and the DRs that describe them may be connected to each other in
a web of trust. Partners in this web may be certification authorities that
verify the truthfulness of claims made in Description Resources. Other
partners may be repositories of thematically linked URIs, such as white lists
for web sites that are recommended for children.</p>

<p>There are several possible models in which assertions and claims can be
made, authenticated and reported to the end user. The Use Cases and
Requirements document lists several use cases which have a number of elements
in common but differ in details such as whether it is the content provider or
the trustmark operator that makes the original claim, whether the data is
stored on the trustmark operator's servers or alongside the content itself,
and whether the trustmark operator provides the description or the
authentication for a description.</p>

<h3><a name="Semantic" id="Semantic">Semantic Annotation</a></h3>

<p>POWDER makes it easy for annotations to be created and published
independently of the relevant content. Such annotations may cover large
amounts of content as it is created with only occasional changes needed to
the annotations. This matches typical content production workflows where
different individuals are often responsible for the two tasks. In situations
where annotation can only be done by the content author, all too often
content is published without any meaningful metadata.</p>

<p>Cost-effective, trusted annotations have a significant potential benefit
to content aggregators, search engines and related services.</p>

<p>Semantic Searches could return results filtered for location-based
cultural parameters. Information provided on the Web can affect users in
different ways depending on the context in which it is retrieved. For
example, nudity on a medical website dealing with breast cancer may be fully
appropriate if it is known prior to retrieval what the context of the content
is. Content promoting discrimination may be appropriate for analysis purposes
but may be served with additional contextual information in other
circumstances. Semantic annotation also allows the disambiguation of terms
such as 'football.'</p>

<p>Furthermore a POWDER document can be used as a set of instructions that
allow a crawler to follow up on all links, pointing to DR in POWDER
documents, to automatically create a triple store about those resources. This
could be used in conjunction with XML-based site maps to create triples by
processing those site maps.</p>

<p>In summary, POWDER empowers users to find more of what they ask for and
less of what they don't.</p>

<h2><a name="does" id="does">3. How does POWDER work in the real
world?</a></h2>

<p>The previous section describes the benefits of POWDER and the reasons why
it is a compelling method for defining relatively small amounts of data that
can be applied to large amounts of content.</p>

<p>The following are brief examples of how POWDER applications work.</p>

<h3><a name="Trustmarks2" id="Trustmarks2">Trustmarks</a></h3>

<p>POWDER offers various possible methods by which trust claims and
assertions can be made and used.</p>

<h4><a name="VISUAL" id="VISUAL">Visual notification</a></h4>

<p>A user could install a browser plug-in designed to provide an indication
(such as a visual logo or audible alarm) that a Web site is trustworthy or
not. The plug-in would rely on various sources such as reputation and
accreditation services to determine trustworthiness.</p>

<h4><a name="MONITORING" id="MONITORING">Monitoring</a></h4>

<p>This can be particularly valuable in cases where certain sites are
required by law or other regulations to provide a certain level of content or
access. Once those sites have been approved and tagged as having met specific
standards, an automated process can aid the discovery and regular review of
the site's content and its DR for continued authenticity and validity. This
could go as far as generating a report for the evaluating party.</p>

<h4><a name="Descriptio" id="Descriptio">Description authentication</a></h4>

<p>A Web site operator submits their work to a trusted organization that can
authenticate the work and provide a Description Resource that identifies the
site as accurate or trustworthy.</p>

<h3><a name="Accessibil" id="Accessibil">Accessibility</a></h3>

<p>POWDER enables search engines and portals, if they so choose, to provide
customized links for users who prioritize compliance with particular
accessibility checks. For example, an organization might review Web sites to
determine their level of compliance with accessibility guidelines [<a
href="#wcag">WCAG</a>]. The reviewed Web sites can be duly tagged as
compliant using a DR supported by a test result expressed in [<a
href="#earl">EARL</a>]. The search engine/portal can then present or perhaps
highlight the best sites based on a user's preference settings and the tags
on the reviewed Web sites. The system can be highly granular so that the
links presented to a user with limited manual dexterity (to resources that
support keyboard navigation) would differ from those presented to a user with
a visual impairment.</p>

<h3><a name="MobileOK" id="MobileOK">MobileOK</a></h3>

<p>In a similar fashion to the accessibility case, POWDER may be used to
identify resources that conform to W3C mobileOK [<a href="#mok">MOK</a>]. A
user wanting to browse the Web using his mobile phone may request that the
search provider favor links suitable for display on his device. When the
search engine retrieves a set of links from its index, it determines which
have an associated mobileOK descriptor, and presents those before the
remainder. </p>

<p>[Example: <a href="#example_mobileOK">mobileOK</a>]</p>

<h3><a name="Child" id="Child">Child Protection</a></h3>

<p>Online child protection, as well as the continuation of offline child
protection, is a priority for any responsible site or service provider,
whether directed at children or not.</p>

<p>A service provider may include a feature that offers parents the ability
to determine the type or level of content they would allow their child to
view. In today's market, most, if not all, service providers do offer some
degree of parental controls. A hypothetical Web site that sells an array of
merchandise can use POWDER to accurately describe their content as either
being child appropriate or intended just for adults. While most of their
content and products are appropriate for all ages, there are also numerous
pages showing "adult" toys. When a child whose setting allows him only to
view content that is age appropriate accesses this online retailer through
the family network he will only be able to view the content that is deemed
age appropriate and not that in the adult category.</p>

<p>[Example: <a href="#ICRA1">ICRA Labelling</a>]</p>

<h3><a name="Functional" id="Functional">Functional User Experience</a></h3>

<p>Web pages and whole Web sites containing any type of rich assets such as
video/streaming video or audio can be tagged with that information using
POWDER. A search engine, content aggregation or adaptation service can then
determine whether a user is accessing content via a low or high bandwidth
connection and return only those pages that contain assets and images that
will be supported by that user's connection speed.</p>

<h3><a name="Privileged" id="Privileged">Privileged Content</a></h3>

<p>A user pays an extra fee to his ISP in order to have privileged access to
third-party premium content. When he accesses a premium page on one of these
third-party Web sites via his ISP, the server is able to recognize him as a
paying customer and deliver the content that has been described as premium by
an associated Description Resource.</p>

<p>Additionally in that fashion a user may be informed that he will not be
able to access said content because he is not a paying customer.</p>

<h3><a name="Semantics" id="Semantics">Semantics</a></h3>

<p>Sites can use Description Resources to communicate the subject matter of
their content more accurately and with greater relevance to user requests.</p>

<h4><a name="Search" id="Search">Search</a></h4>

<p>Because the same term can suggest two distinctly different meanings, the
judicious use of Description Resources can go a long way in making a site
more valuable to a greater number of people. An owner of a global sports site
can provide descriptors that are accurate enough so that users searching on
the term "football" can receive the portions of the available content
relating to the specific game that the user's location suggests is what they
are searching for information about.</p>

<h4><a name="Distinguis" id="Distinguis">Distinguishing opinion</a></h4>

<p>By developing an appropriate and detailed vocabulary, Description
Resources can be used to identify the value of a site as being either of
value in its own right or as an excellent example of something that is
intrinsically bad (in the opinion of the DR author).</p>

<h2><a name="POWDER" id="POWDER">4. How do I use POWDER?</a></h2>

<p>Usage of POWDER is dependent on the intended results.</p>
<ul>
  <li>If the goal is to simply provide meta data in a new and efficient
    fashion, it is enough to create Description Resources in XML which can be
    read and used by the appropriate tools</li>
  <li>If the goal is to use such meta data semantically, it is necessary to
    convert the XML document into RDF data.</li>
</ul>

<p>The process is a sequence and can be stepped through all the way or
terminated at the appropriate place to obtain the desired result. </p>

<p>For someone who wishes to describe content:</p>
<ol>
  <li>Create one or more Description Resources within a POWDER document and
    make it available on the Web. <br />
    This requires no more than the generation of an XML document that
    contains the necessary components of a Description Resource.<br />
    No further steps are necessary, other than publishing, to create a
    Description Resource and thus offer this meta data publicly. <br />
    <br />
  </li>
  <li>Make the POWDER document discoverable<br />
    This is no more than making sure that DRs can be accessed by the intended
    audience, most likely the Web.<br />
    You should link from the described resources to the POWDER document. <br
    />
    It is also possible to describe someone else's content.<br />
    <br />
  </li>
  <li>Add trust to your descriptions<br />
    Trust is an integral component of POWDER documents. Choose a method,
    ranging from simply publishing your document, thereby making a claim, to
    providing fully certified POWDER documents with supporting resources to
    add trust to your DRs. </li>
</ol>

<p>For someone who wants to access RDF triples obtained from POWDER
documents:</p>
<ol>
  <li>A POWDER processor must be used to read and process POWDER documents to
    obtain RDF triples that describe specific Web resources. Refer to the [<a
    href="#dr">DR</a>] document for POWDER processor details. </li>
  <li>Now an RDF querying tool could be used to retrieve:
    <ul>
      <li>descriptions of a resource </li>
      <li>the set of resources that have a given property, e.g. all web pages
        that are mobileOK</li>
    </ul>
  </li>
</ol>

<p>As an alternative, someone may want to draw inferences based on the data
contained in POWDER documents.<br />
Drawing an inference means deriving implicit information from known facts.
<br />
For example:</p>
<ul>
  <li>I know that everything on example.com conforms to accessibility level
  AA</li>
  <li>A resource of interest is located on example.com</li>
</ul>

<p>Therefore that particular resource conforms to accessibility level AA.</p>

<p>In order to do so, the following steps should be followed.</p>
<ol>
  <li>Convert the POWDER document into a POWDER-S document (intended for
    semantic web usage, via the GRDDL transform defined in the Formal
    Semantics document [<a href="#formal">FORMAL</a>]<br />
  </li>
  <li>Now an inference engine must be used to retrieve the property of a
    given resource. <br />
    For this step it is important to realize that an extension to RDF/OWL has
    to be implemented in the reasoning engine in order to support and utilize
    POWDER-S</li>
</ol>

<p>Following the example above we could now determine which resources on
example.com are AA conformant, as well as the conformance level of a given
resource.</p>

<h3><a name="create" id="create">How do I create a Description
Resource?</a></h3>

<p>The first step is to create a skeleton POWDER document in XML and declare
the namespaces:</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;powder
  xmlns="http://www.w3.org/2007/05/powder#"
  xmlns:ex="http://example.org/vocab#"&gt;
&lt;/powder&gt;</pre>

<p>Any descriptive vocabularies may be used which are identified by a
namespace. The POWDER namespace is required.</p>

<p>The "ex" namespace used above is a fictitious example to denote that any
namespace may be used.</p>

<p>Next we need to say who has created the document. All POWDER documents
have exactly one <code>attribution</code> element, and within that an
<code>issuedby</code> element. This points to details of the person or
organization that has published the POWDER document. Exactly which details is
for the publisher to decide, but a name and a homepage address should usually
be included, perhaps along with contact details. POWDER authors may use
either the Friend of a Friend [<a href="#foaf">FOAF</a>] vocabulary or the
Dublin Core [<a href="#dc">DC</a>] to do this.</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;powder
  xmlns="http://www.w3.org/2007/05/powder#"
  xmlns:ex="http://example.org/vocab#"
    <b>&lt;attribution&gt;
     &lt;issuedby src="http://authority.example.org/company.rdf#me" /&gt;
    &lt;/attribution&gt;</b>
&lt;/powder&gt;</pre>

<p>An individual or organization may publish many Description Resources.
Therefore it is more convenient to define the profile information, describing
that individual or organization, in a single file and refer to it from each
POWDER document as it is created. The above example points to a profile as
listed below. Notice the rdf:ID="me", which is referred to by the #me in the
above example.</p>

<p>The publisher's profile would look similar to this:</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;rdf:RDF
   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   xmlns:foaf="http://xmlns.com/foaf/0.1/"&gt;
  &lt;foaf:Organization rdf:ID="me"&gt;
    &lt;foaf:name&gt;The POWDER Company&lt;/foaf:name&gt;
    &lt;foaf:homepage rdf:resource="http://authority.example.org" /&gt;
  &lt;/foaf:Organization&gt;
&lt;/rdf:RDF&gt;</pre>

<p>A POWDER document will typically also include information about when it
was created (our example was created on 14 December 2007).</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;powder
   xmlns="http://www.w3.org/2007/05/powder#"&gt;
  &lt;attribution&gt;
    &lt;issuedby src="http://authority.example.org/company.rdf#me" /&gt;
    <strong>&lt;issued&gt;2007-12-14T00:00:00&lt;/issued&gt;</strong>
  &lt;/attribution&gt;
&lt;/powder&gt;</pre>

<p>Next an actual Description Resource (DR) is added. This example POWDER
document will contain a single Description Resource, as the <code>dr</code>
element.</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;powder
   xmlns="http://www.w3.org/2007/05/powder#"&gt;
  &lt;attribution&gt;
    &lt;issuedby src="http://authority.example.org/company.rdf#me" /&gt;
    &lt;issued&gt;2007-12-14T00:00:00&lt;/issued&gt;
  &lt;/attribution&gt;
  <strong>&lt;dr&gt;
  &lt;/dr&gt;</strong>
&lt;/powder&gt;</pre>

<p>The Description Resource itself must contain at least one set of IRIs.
This is the scope of the Description Resource - i.e. what it describes. IRIs
are a superset of the well known Uniform Resource Identifier (URI) with the
expansion of also allowing international characters. If multiple IRI sets are
included within a DR, then the scope is all the IRIs in all the IRI sets.</p>

<p>In this case, the scope is 'everything on example.com'. This is done using
the <code>includehosts</code> element. There are other elements available
which are described in detail in the Grouping of Resources document [<a
href="#group">GROUP</a>]. All Description Resources must contain at least one
iriset element, and this cannot be empty and cannot contain any elements from
any other namespace.</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;powder
   xmlns="http://www.w3.org/2007/05/powder#"&gt;
  &lt;attribution&gt;
    &lt;issuedby src="http://authority.example.org/company.rdf#me" /&gt;
    &lt;issued&gt;2007-12-14T00:00:00&lt;/issued&gt;
  &lt;/attribution&gt;
  &lt;dr&gt;
    <strong>&lt;iriset&gt;
      &lt;includehosts&gt;example.com&lt;/includehosts&gt;
    &lt;/iriset&gt;</strong>
  &lt;/dr&gt;
&lt;/powder&gt;</pre>

<p>The final key element of a Description Resource is the actual description.
There are two ways of providing this.</p>
<ul>
  <li>As RDF (in a "descriptor set")</li>
  <li>As one or more tags (in a "tag set")</li>
</ul>

<p>A DR must contain at least one of either a descriptor set or tag set, none
of which may be empty. Subject to that condition, any number of tag sets and
descriptor sets may be included. The example DR states that in the opinion of
the entity referenced by the <code>issuedby</code> element, all resources
within its scope are described by all descriptive elements. </p>

<p>We'll add one of these to our example: a descriptor set. It may contain
RDF/XML properties with literal values (including XML literals) or resources
identified by an IRI. In addition, a textual and/or graphic summary that can
be displayed to end users may be included in a descriptor set using the
<code>displaytext</code> and <code>displayicon</code> elements as shown in
the completed example below. Notice that the namespace used in the descriptor
set is also highlighted.</p>

<div class="example">
<p class="caption">Generic Example of a POWDER Document Containing a Single
Description Resource. </p>

<p>This is a repeat of Example 2-1 in the Description Resources document [<a
href="#dr">DR</a>]</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;powder xmlns="http://www.w3.org/2007/05/powder#"
        <b>xmlns:ex="http://example.org/vocab#</b>"&gt;

  &lt;attribution&gt;
    &lt;issuedby src="http://authority.example.org/company.rdf#me" /&gt;
    &lt;issued&gt;2007-12-14T00:00:00&lt;/issued&gt;
  &lt;/attribution&gt;

  &lt;dr&gt;

    &lt;iriset&gt;
      &lt;includehosts&gt;example.com&lt;/includehosts&gt;
    &lt;/iriset&gt;

    <b>&lt;descriptorset&gt;
      &lt;ex:color&gt;red&lt;/ex:color&gt;
      &lt;ex:shape&gt;square&lt;/ex:shape&gt;
      &lt;displaytext&gt;Everything on example.com is red and square&lt;/displaytext&gt;
      &lt;displayicon src="http://authority.example.org/icon.png" /&gt;
    &lt;/descriptorset&gt;</b>

   &lt;/dr&gt;

&lt;/powder&gt;</pre>
</div>


<p>Of course, much more complicated structures are possible than this simple
example.</p>

<p>The following example uses an ordered list of DRs. In such a list 0 or 1,
DRs will apply to a given resource. A processor will work through the list
until the first match is found. This feature is designed to make it easy to
add POWDER descriptions to existing content within established workflows.
Effectively it enables a list of exception to be created, ending with the
general case.</p>

<p>NOTE: The example below contains an <code>abouthosts</code> element which
may be used by a processor to decide if a list, perhaps a long list, need be
processed at all. Here we know that only resources on example.com are
described in the ordered list, however it is important to recognize that this
does not guarantee that all resources on example.com are described.</p>

<div class="example">
<p class="caption">Example of a POWDER document which contains an ordered
list</p>

<p>This is a repeat of from Example 2-6 in the Description Resources document
[<a href="#dr">DR</a>]</p>
<pre>&lt;?xml version="1.0"?&gt;
&lt;powder xmlns="http://www.w3.org/2007/05/powder#"
      xmlns:ex="http://example.org/vocab#"&gt;

  &lt;attribution&gt;
    &lt;issuedby src="http://authority.example.org/company.rdf#me" /&gt;
    &lt;issued&gt;2007-12-14T00:00:00&lt;/issued&gt;
    &lt;abouthosts&gt;example.com&lt;/abouthosts&gt;
  &lt;/attribution&gt;

  &lt;ol&gt;

    &lt;dr&gt;
      &lt;iriset&gt;
         &lt;includehosts&gt;example.com&lt;/includehosts&gt;
         &lt;includepathstartswith&gt;/foo&lt;/includepathstartswith&gt;
      &lt;/iriset&gt;
      &lt;descriptorset&gt;
        &lt;ex:color&gt;blue&lt;/ex:color&gt;
      &lt;/descriptorset&gt;
    &lt;/dr&gt;

    &lt;dr&gt;
      &lt;iriset&gt;
        &lt;includehosts&gt;example.com&lt;/includehosts&gt;
      &lt;/iriset&gt;
      &lt;descriptorset&gt;
        &lt;ex:color&gt;red&lt;/ex:color&gt;
      &lt;/descriptorset&gt;
    &lt;/dr&gt;

  &lt;/ol&gt;

&lt;/powder&gt;</pre>
</div>

<p>The example above encodes the following assertion made by the entity
described at http://authority.example.org/company.rdf#me: all web resources
with paths on example.com that start with /foo are blue, all other resources
on example.com are red. </p>

<p>POWDER offers other methods of defining the scope of DRs that are designed
to increase flexibility. For example, it is possible for the scope of a DR to
be the union of two or more IRI sets, meaning that an IRI that is a member of
any IRI set is described. The following example describes resources that are
available from example.com where the path starts with /foo AND those at
example.org where the path starts with /bar.</p>

<div class="example">
<p class="caption">Example of a POWDER document with two IRI sets</p>

<p>This is a repeat of Example 2-8 in the Description Resources document [<a
href="#dr">DR</a>]</p>
<pre>&lt;?xml version="1.0"?&gt;
  &lt;powder xmlns="http://www.w3.org/2007/05/powder#"
          xmlns:ex="http://example.org/vocab#"&gt;
    &lt;attribution&gt;
      &lt;issuedby src="http://authority.example.org/company.rdf#me" /&gt;
      &lt;issued&gt;2007-12-14T00:00:00&lt;/issued&gt;
    &lt;/attribution&gt;

    &lt;dr&gt;
      &lt;iriset&gt;
        &lt;includehosts&gt;example.com&lt;/includehosts&gt;
        &lt;includepathstartswith&gt;/foo&lt;/includepathstartswith&gt;
      &lt;/iriset&gt;

      &lt;iriset&gt;
        &lt;includehosts&gt;example.org&lt;/includehosts&gt;
        &lt;includepathstartswith&gt;/bar&lt;/includepathstartswith&gt;
      &lt;/iriset&gt;

      &lt;descriptorset&gt;
        &lt;ex:color&gt;red&lt;/ex:color&gt;
        &lt;ex:shape&gt;square&lt;/ex:shape&gt;
        &lt;displaytext&gt;Everything on example.com/foo, and everything on example.org/bar, is red and square&lt;/displaytext&gt;
        &lt;displayicon src="http://example.org/icon.png" /&gt;
      &lt;/descriptorset&gt;
    &lt;/dr&gt;
  &lt;/powder&gt;</pre>
</div>

<h3><a name="publish" id="publish">How do I publish a DR?</a></h3>

<p>Like any other resource on the Web, POWDER documents can only be found if
you know where to look or you can follow a link from where you already are.
Individuals or organizations whose activities include reviewing and
describing online content will be able to set up and advertise the existence
of a repository of Description Resources.</p>

<p>There are several methods of linking from a resource to a POWDER document
that describes it. <br />
First of all, HTML documents can include a link element in much the same way
as is common for linking to CSS style sheets, RSS/ATOM feeds, etc.</p>
<pre>&lt;link rel="describedby" href="powder.xml" type="application/powder+xml"/&gt;</pre>

<p>The relationship type (rel) of "describedby" tells user agents that the
file contains a description of the resource and the mime type tells it that
it is a POWDER document. The value of the href is the IRI of the POWDER
document. </p>

<p>Just as with stylesheets, it's important to include this link on all
described pages, so it is best included in the document template.</p>

<p>When using HTML link elements in this way, authors should also refer to
POWDER's <a href="http://www.w3.org/2007/11/powder-profile">profile
document</a> as shown below, if using an HTML version that supports it.</p>
<pre>&lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
   &lt;head profile="http://www.w3.org/2007/11/powder-profile"&gt;
      &lt;meta name="wdr.issuedby" content="http://authority.example.org/company.rdf#me"/&gt;
      &lt;link rel="describedby" href="powder.xml" type="application/powder+xml"/&gt;
      &lt;title&gt;Welcome to example.com &lt;/title&gt;
   &lt;/head&gt;
   &lt;body&gt;
      &lt;p&gt;Today's content is ....&lt;/p&gt;
   &lt;/body&gt;
&lt;/html&gt;</pre>


<p>Adding this makes the relationship type "describedby" clear and allows
content authors to include data about the POWDER document within the
described resource. As shown in the example above, this can include
information about who has issued the DRs (issuedby), so that a user agent
that recognizes and trusts that Description Resource author will be more
confident that the data available is trustworthy and therefore that the link
is worth following.<ins></ins></p>

<p>Whilst HTML link elements do make POWDER documents discoverable, the
preferred method is to configure the server to include an HTTP Response
Header that does the same job.</p>
<pre>Link: &lt;powder.xml&gt;; rel="describedby"; type="application/powder+xml";</pre>

<p>This has several distinct advantages:</p>
<ol>
  <li>It allows all resources, not just HTML documents, to point to a POWDER
    document.</li>
  <li>It allows the POWDER document to be discovered and parsed
    <em>before</em> the described content is parsed.</li>
  <li>In some content production environments the process of configuring
    servers can be easier to achieve and lead to longer-term stability than
    changing templates.</li>
</ol>

<p>Where POWDER documents are discoverable via HTTP Link: headers, a user
agent or Web crawler can discover them by doing an HTTP HEAD request which
may affect how, or indeed whether, a subsequent GET request is made. </p>

<p>The describedby relationship type is made available as an RDF property,
where a more formal relationship between a POWDER document and a resource
that it describes is required. This may be used, for example, in XHTML
documents annotated with RDFa as described in section 4.1.3 of the
Description Resources document [<a href="#dr">DR</a>]. One important benefit
of using RDFa to link to POWDER documents is that it allows you to point to a
description of the destination of a hyperlink.</p>

<p>As an example of this, imagine an XHTML document about a rock band that
includes hyperlinks to ring tones, images and videos.</p>

<div class="example" id="rdfa-eg">
<p class="caption">An XHTML/RDFa Fragment with Hyperlinks described using
POWDER</p>
<pre>&lt;ul&gt;
  &lt;li&gt;&lt;a href="/clips/low_res_clip.mpg"
         rev="wdrs:describedby"
         about="/powder.xml"&gt;30" clip&lt;/a&gt;&lt;/li&gt;

  &lt;li&gt;&lt;a href="/videos/full_video.mpg"
         rev="wdrs:describedby"
         about="/powder.xml"&gt;Full 10 minute video&lt;/a&gt;&lt;/li&gt;

  &lt;li&gt;&lt;a href="/tones/ring_tone1.mp3"
         rev="wdrs:describedby"
         about="/powder.xml"&gt;Ring Tone&lt;/a&gt;&lt;/li&gt;

  &hellip;

&lt;/ul&gt;</pre>

<p class="caption">powder.xml</p>
<pre>&lt;ol&gt;
  &lt;dr&gt;
    &lt;iriset&gt;
       &lt;includehosts&gt;example.com&lt;/includehosts&gt;
       &lt;includepathcontains&gt;/videos/&lt;/includepathcontains&gt;
    &lt;/iriset&gt;
    &lt;tagset&gt;
      &lt;tag&gt;Large download&lt;/tag&gt;
      &lt;label&gt;Only suitable for download via high-bandwidth connections&lt;/label&gt;
    &lt;/tagset&gt;
  &lt;/dr&gt;

  &lt;dr&gt;
    &lt;iriset&gt;
       &lt;includehosts&gt;example.com&lt;/includehosts&gt;
    &lt;/iriset&gt;
    &lt;descriptorset&gt;
      &lt;typeof src="http://www.w3.org/2008/06/mobileOK#conformant" /&gt;
    &lt;/descriptorset&gt;
  &lt;/dr&gt;
&lt;/ol&gt;</pre>
</div>

<p>This ordered list of DRs states that resources on the example.com host
where the IRI path includes /videos/ are large downloads. All other resources
on example.com are conformant with mobileOK [<a href="#mok">MOK</a>]. By
taking note of the available descriptions, the user agent may display the
links differently on different devices (or chose not to display them at
all).</p>

<p>Notice a couple of points here:</p>
<ol>
  <li>Use of the "rev" attribute which reverses the relationship so that
    "powder.xml" is "about" the hyperlink.</li>
  <li>The same POWDER document contains both the DRs and can therefore be
    used from cache.</li>
</ol>

<h3><a name="ensuretrust" id="ensuretrust">How do I make my DR more
trustworthy?</a></h3>

<p>Trust is a critical aspect of Description Resources; however, trust is
very much a matter of opinion. The level of trust demanded of a given DR will
depend on what the description says and to what use it will be put. For
example, an individual user finding a DR that declares a Web site to offer
children's birthday party ideas can make his/her own assessment of its
quality and usefulness. In contrast, a multi-million dollar business will
need very strong assurance that a DR declaring a Web site to be medically
accurate and freely available is trustworthy before including it in a portal
of high quality, license-free health care materials. For this reason, we do
not define a single trust mechanism that must be used. Rather, there are a
variety of different methods of adding trust to DRs, some of which may be
used in combination.</p>
<ul>
  <li>Publish the DR in a trusted location, for example under the main domain
    for a well-known content provider.</li>
  <li>Provide links to the author of a DR. Use the <code>authenticate</code>
    property to point from the author's profile to information about how a
    user (or user agent) can verify a DR. This is not limited to persons, but
    can be used for organizations and other entities.</li>
  <li>Provide validity and issue date information. This will let users know
    how up to date the claim is.</li>
  <li>Have claims certified by independent and trusted third parties.</li>
  <li>Point to such certifications by using the <code>certifiedby</code>
    property.</li>
  <li>Link to supporting information using the <code>supportedby</code>
    property. This points to further DRs or other Web resources that contain
    information supporting the claim made.</li>
</ul>

<p>Where applicable, we define vocabulary terms designed to aid the building
of trust.</p>

<p>The methods cited here do not comprise an exhaustive list. Other
techniques, such as XML Signature [<a href="#xmlsig">XMLSIG</a>] and Web of
Trust [<a href="#wot">WOT</a>], may be equally applicable. Trust is a human
judgment that can only be made by weighing the likelihood that the data is
true against the consequences of it being false. This judgment is highly
dependent on the circumstances under which the need to extend trust arises.
It is clear, however, that Description Resources are unlikely to be trusted
in isolation and that both their publishers and consumers will only benefit
from their existence if one or more techniques for enhancing trust are
employed.</p>

<p>These methods would also serve to increase trust placed in the meta
information provided for Web documents in general. Today's meta data, such as
the keywords provided in META elements, can have little value as this
mechanism has been abused to such a degree that renders it practically
useless from an informational point of view. Search engines do not place much
stock on keywords to give any indication about the relevance of a given Web
page to a given topic and use different means, such as incoming links, as a
basis for page ranking. False claims made in meta information, intended to
lure the user into clicking on a link to a resource, also serve to lower the
value of meta information.</p>

<p>Also, a less deliberate yet still disturbing, fact about meta information
is aging. As meta information is not kept up to date, it loses its relevance
to the content it describes. POWDER elevates meta information once again into
the spotlight by allowing a third-party to certify the veracity of the meta
information given, declare the date of the verification, and define a date
after which the certificate will no longer be valid.</p>

<h3><a name="find" id="find">How do I find DRs for a document?</a></h3>

<p>DRs should describe reflect Web resources in their current state. This
requires that DRs are kept up-to-date and will thus change frequently.
Therefore it is important to provide a link to the "latest" version of DR
document, which has the added benefit of providing a DR history. If a request
is then made for this document, an HTTP 302 redirect can be used to point the
requesting client to the actual, current POWDER document.</p>

<p>A further option would be querying a known repository of DRs. Since the
creation of DRs is not limited to the author or provider of a Web resource,
repositories of DRs may be created by companies or special interest groups,
for example those specializing in standards compliance certification or child
protection. These may then be queried to obtain descriptions and scope
information. For example, a large content provider, upon planning to switch
from regular meta data to POWDER, could, in a first step, create one or
several DR documents. The scope would be set such as to cover all areas of
the content provider's content. Meta elements and various other information
may be copied into the DR documents. Insertion of the appropriate link in the
web resource, pointing to the correct DR, would be the last step prior to
publication of the DR documents.</p>

<p>Personal collections of DRs may be traded or passed between users of
social networks or other groupings of similar interests. Search engines'
indexes may also contain references to publically available DRs.</p>

<p>In short, DRs are normal documents that may be discovered in all the usual
ways that other documents are discovered on the Web.</p>

<h3><a name="process-docs" id="process-docs">How do I process POWDER
documents?</a></h3>

<p>A POWDER Processor accepts queries for descriptions of specific resources
which it generates by reading POWDER documents and returning RDF triples.
There is a minimal set of requirements for a conformant POWDER processor
given in the Description Resources document [<a href="#dr">DR</a>] where
implementers are encouraged to go further than the minimum. A POWDER
Processor may act as a gateway to a repository of DRs and use that as its
only source of data, or it may be more generalized, accepting both the IRI to
be described and one or more POWDER documents as the source from which to
generate the description. The application environment will determine which
factors are important but it is of course useful to think about usability,
error trapping and potential extensions of its functionality.</p>

<h3><a name="process1" id="process1">How do I process POWDER-S?</a></h3>

<p>The operational semantics, meaning the XML file, are underpinned by formal
semantics. A GRDDL transform is associated with the POWDER namespace that
allows the XML data to be rendered and processed as RDF/OWL.</p>

<p>However, RDF/OWL cannot currently interpret string values of RDF
properties as International Resource Identifiers (IRI). In other words the
string "http://example.org" is not necessarily recognized as the web address
(IRI) http://example.org.</p>

<p>To allow this to happen a semantic extension has to be created that makes
this definition and relates to the <code>matchesregex</code> property. The
extension is defined in <a href="#formal">POWDER: Formal Semantics</a></p>

<h2><a name="What1" id="What1">5. What do I need to use POWDER?</a></h2>

<h3 id="basic_reqs">Basic requirements</h3>

<p>No special knowledge is needed to understand plain POWDER. </p>

<p>The examples provided in the documents should be sufficient to begin using
POWDER with only rudimentary knowledge of markup languages.</p>

<p>You will need to be able to publish (upload) the POWDER web descriptions
to some location (server) where people can reach (download) them.</p>

<p>This may be the same location as the web resources themselves.</p>

<h3 id="create_dr">Creation of a DR</h3>

<p>The creation of a DR could be accomplished via online tools provided by
companies who offer repositories of DRs or created by hand with a desktop
editor in the simple form outlined in this document. In that case all that is
needed, if so desired, is to link from the web resource to the DR via a link
element or other mechanism as outlined here.</p>

<h2><a name="powder-s" id="powder-s">6. POWDER-S</a></h2>

<p>POWDER-S is not be dealt with in great detail in this document since it is
essentially an extension of RDF and OWL which are fully documented elsewhere.
The interested reader is encouraged to consult the [<a
href="#formal">FORMAL</a>] specification, which outlines POWDER-S
exhaustively.</p>

<p>The FORMAL specification provides the necessary underpinning for POWDER
and POWDER-S such that processing done on these types of documents can be
conformant and consistent with existing Semantic Web technologies.
Furthermore, the Grouping specification [<a href="#group">GROUP</a>] also
outlines the support for non-url environments, e.g. ISBN codes or similar
resources.</p>

<p>It should be noted, however, that the creation of POWDER-S documents
requires the implementation of an RDF extension in the reasoning engine.</p>

<p>See Section 4.3 POWDER-S IRI Set Semantics in the Formal document [<a
href="#formal">FORMAL</a>] for details.</p>

<div class="example">
<p class="caption">Generic example of a POWDER-S Document Containing a Single
Description Resource</p>

<p>This is a repeat of Example 2-3 from the Description resources document
[<a href="#dr">DR</a>]</p>
<pre>1  &lt;?xml version="1.0"?&gt;
2  &lt;rdf:RDF
3     xmlns:wdrs="http://www.w3.org/2007/05/powder-s#"
4     xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
5     xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
6     xmlns:owl="http://www.w3.org/2002/07/owl#"
7     xmlns:ex="http://example.org/vocab#"&gt;
8
9    &lt;owl:Ontology rdf:about=""&gt;
10     &lt;wdrs:issuedby rdf:resource="http://authority.example.org/company.rdf#me" /&gt;
11     &lt;wdrs:issued&gt;2007-12-14T00:00:00&lt;/wdrs:issued&gt;
12   &lt;/owl:Ontology&gt;
13
14   &lt;owl:Class rdf:nodeID="iriset_1"&gt;
15     &lt;owl:equivalentClass&gt;
16       &lt;owl:Class&gt;
17         &lt;owl:intersectionOf rdf:parseType="Collection"&gt;
18           &lt;owl:Restriction&gt;
19             &lt;owl:onProperty rdf:resource="http://www.w3.org/2007/05/powder-s#matchesregex" /&gt;
20             &lt;owl:hasValue rdf:datatype="http://www.w3.org/2001/XMLSchema#string"&gt;\:\/\/(([^\/\?\#]*)\@)?([^\:\/\?\#\@]+\.)?(example\.com)(:([0-9]+))?\/&lt;/owl:hasValue&gt;
21           &lt;/owl:Restriction&gt;
22         &lt;/owl:intersectionOf&gt;
23       &lt;/owl:Class&gt;
24     &lt;/owl:equivalentClass&gt;
25   &lt;/owl:Class&gt;
26
27   &lt;owl:Class rdf:nodeID="descriptorset_1"&gt;
28     &lt;rdfs:subClassOf rdf:resource="http://www.w3.org/2002/07/owl#Thing"/&gt;
29     &lt;rdfs:subClassOf&gt;
30       &lt;owl:Class&gt;
31         &lt;owl:intersectionOf rdf:parseType="Collection"&gt;
32           &lt;owl:Restriction&gt;
33             &lt;owl:onProperty rdf:resource="http://example.org/vocab#color" /&gt;
34             &lt;owl:hasValue&gt;red&lt;/owl:hasValue&gt;
35           &lt;/owl:Restriction&gt;
36           &lt;owl:Restriction&gt;
37             &lt;owl:onProperty rdf:resource="http://example.org/vocab#shape" /&gt;
38             &lt;owl:hasValue&gt;square&lt;/owl:hasValue&gt;
39           &lt;/owl:Restriction&gt;
40         &lt;/owl:intersectionOf&gt;
41       &lt;/owl:Class&gt;
42     &lt;/rdfs:subClassOf&gt;
43     &lt;wdrs:text&gt;Everything on example.com is red and square&lt;/wdrs:text&gt;
44     &lt;wdrs:logo rdf:resource="http://example.org/icon.png" /&gt;
45   &lt;/owl:Class&gt;
46
47   &lt;rdf:Description rdf:nodeID="iriset_1"&gt;
48     &lt;rdfs:subClassOf rdf:nodeID="#descriptorset_1"/&gt;
49   &lt;/rdf:Description&gt;
50
51 &lt;/rdf:RDF&gt;</pre>
</div>

<p>Line-by-line explanation:</p>
<dl>
  <dt>Lines 1-7</dt>
    <dd>Document header: with namespace declarations</dd>
  <dt>Lines 9-12</dt>
    <dd>Attribution: Each POWDER-S document is an OWL ontology and the
      attribution section is an ontology header.</dd>
  <dt>Lines 14-25</dt>
    <dd>Scope: An OWL class acts as the IRI set. It is this class that makes
      use of the <code>matchesregex</code> property which is only understood
      by software that implements the semantic extension which confers
      membership of the class on resources whose IRIs match the given regular
      expression(s). <span id="xq">The regular expression syntax used is defined by XML
	schema as modified by XQuery 1.0 and XPath 2.0 Functions and
	Operators [<a href="#xqxp">XQXP</a>].</span></dd>
  <dt>Lines 27-45</dt>
    <dd>Description: These are the actual descriptors.</dd>
  <dt>Lines 47-49</dt>
    <dd>Assertion: The encoding of the DR is completed by asserting that the
      IRI set is a subclass of the descriptor set. This is the crucial step
      that allows the inference to be drawn about members of the IRI set.</dd>
</dl>

<h2><a name="examples" id="examples">7. Examples</a></h2>

<h3><a name="ICRA1" id="ICRA1">ICRA Labelling</a></h3>

<p>The <a href="http://www.icra.org/vocabulary/" name="ICRA" id="ICRA">ICRA
vocabulary</a> facilitates what is intended to be a culturally neutral
description of online content in terms that may reflect parental concerns
around the world. Such descriptions, especially where backed up by
third-party checks, can be useful in delivering appropriate content to
different target groups, particularly children.</p>

<p>In the following scenario, we imagine that example.com publishes content
across its portal that does not include any sex, nudity, violence or other
potentially offensive or harmful material, <strong>except</strong> in its
night life section, where references to alcohol, tobacco and potentially
offensive language are to be found, especially as it invites users to post
reviews of bars, pubs and clubs they have visited. Since all pages relevant
to the night life section have a URL of the form
http://www.example.com/nightlife... it is able to describe its own content in
the following POWDER document.</p>

<div class="example">
<p class="caption">Example: ICRA labelling <a
href="icra_example.xml">[XML]</a></p>
<pre>1  &lt;?xml version="1.0"?&gt;
2  &lt;powder xmlns="http://www.w3.org/2007/05/powder#"
3          xmlns:foaf="http://xmlns.com/foaf/0.1/"
4          xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
5          xmlns:icra="http://www.icra.org/rdfs/vocabulary2008#"&gt;
6
7    &lt;attribution&gt;
8      &lt;issuedby src="http://www.example.com/company.rdf#me" /&gt;
       &lt;issued&gt;2008-06-02T00:00:00&lt;/issued&gt;
15     &lt;certifiedby src="http://independent.example.org?verify=http%3A%2F%2Fwww.example.com%2Fpowder.xml" /&gt;
16   &lt;/attribution&gt;
17
18   &lt;ol&gt;
19     &lt;dr&gt;
20       &lt;iriset&gt;
21         &lt;includehosts&gt;example.com&lt;/includehosts&gt;
22         &lt;includepathstartswith&gt;/nightlife&lt;/includepathstartswith&gt;
23       &lt;/iriset&gt;
24
25       &lt;descriptorset&gt;
26         &lt;icra:nz&gt;1&lt;/icra:nz&gt;
27         &lt;icra:sz&gt;1&lt;/icra:sz&gt;
28         &lt;icra:vz&gt;1&lt;/icra:vz&gt;
29         &lt;icra:lb&gt;1&lt;/icra:lb&gt;
30         &lt;icra:lc&gt;1&lt;/icra:lc&gt;
31         &lt;icra:ha&gt;1&lt;/icra:ha&gt;
32         &lt;icra:hb&gt;1&lt;/icra:hb&gt;
33         &lt;icra:dz&gt;1&lt;/icra:dz&gt;
34         &lt;icra:ua&gt;1&lt;/icra:ua&gt;
35         &lt;icra:pa&gt;1&lt;/icra:pa&gt;
36         &lt;displaytext&gt;
               No nudity; No sexual material; No violence;
               Profanity or swearing; Mild expletives;
               Depiction of tobacco or its use; Depiction of alcohol or its use;
               No potentially disturbing material;
               User-generated content such as chat rooms and message boards (moderated);
               Contains advertising
           &lt;/displaytext&gt;
37       &lt;/descriptorset&gt;
38     &lt;/dr&gt;
39
40     &lt;dr&gt;
41       &lt;iriset&gt;
42         &lt;includehosts&gt;example.com&lt;/includehosts&gt;
43         <span id="typo">&lt;excludepathstartswith&gt;/nightlife&lt;/excludepathstartswith&gt;</span>
44       &lt;/iriset&gt;
45
46       &lt;descriptorset&gt;
47         &lt;icra:nz&gt;1&lt;/icra:nz&gt;
48         &lt;icra:sz&gt;1&lt;/icra:sz&gt;
49         &lt;icra:vz&gt;1&lt;/icra:vz&gt;
50         &lt;icra:lz&gt;1&lt;/icra:lz&gt;
51         &lt;icra:hz&gt;1&lt;/icra:hz&gt;
52         &lt;icra:dz&gt;1&lt;/icra:dz&gt;
53         &lt;icra:uz&gt;1&lt;/icra:uz&gt;
54         &lt;icra:pa&gt;1&lt;/icra:pa&gt;
55         &lt;displaytext&gt;
               No nudity; No sexual material; No violence;
               No potentially offensive language;
               No potentially harmful activities;
               No potentially disturbing material;
               No user-generated content; Contains advertising
           &lt;/displaytext&gt;
56       &lt;/descriptorset&gt;
57     &lt;/dr&gt;
58   &lt;/ol&gt;
59
60 &lt;/powder&gt;</pre>
</div>


<p>The document contains two Description Resources that reflect the two
different types of content on (the fictional) example.com. This document
makes use of POWDER's ordered list feature such that <strong>every</strong>
page on example.com, irrespective of its content, can be linked to the same
file. This can be done by including a link element in each page's HTML
thus:</p>

<p><code>&lt;link rel="describedby" href="/powder.xml" type="application/powder+xml"
title="ICRA labels" /&gt;</code></p>

<p>but is more efficiently done by configuring the example.com server(s) to
include the equivalent HTTP Link header thus:</p>

<p><code>Link: &lt;/powder.xml&gt;; rel="describedby";
type="application/powder+xml";</code></p>

<p>A user agent, such as a content aggregation service, can now support
different policies with respect to the resources available from example.com.
It may, for example, choose not to include the night life section for all its
customers, or conversely to promote that section as it is a better fit for
its own target market.</p>

<p>Notice also that example.com has referred to an independent certification
body in Line 15. A user agent might be satisfied that example.com's
description of its own content is sufficiently trustworthy to be of use or it
may choose to query the service operated by http://independent.example.org
before conferring trust on the data. In the specific case of ICRA
descriptions, it is often the case that a description of content as being
potentially harmful or offensive is trusted more readily than descriptions of
content as being suitable for children. Thus external verification mechanisms
can have varying degrees of importance even within a single domain of
interest.</p>

<h3><a name="example_mobileOK" id="example_mobileOK">mobileOK</a></h3>

<p>mobileOK is a standard that deals with content that is rendered within a
mobile context and adheres to a set of guidelines called the mobileOK Basic
Tests. Claiming mobileOK has been one of the major use cases of POWDER and
the example below outlines how this claim can be made using a POWDER
document.</p>

<div class="example">
<p class="caption">Example: mobileOK (from Example 5-3: A DR Claiming
Conformance to mobileOK Basic, Supported By the mobileOK Basic Checker [<a
href="mobileOK_example.xml">XML</a>]</p>
<pre>1  &lt;?xml version="1.0"?&gt;
2  &lt;powder xmlns="http://www.w3.org/2007/05/powder#"&gt;

3    &lt;attribution&gt;
4      &lt;issuedby src="http://www.example.com/company.rdf#me" /&gt;
5      &lt;issued&gt;2008-06-25T00:00:00&lt;/issued&gt;
6      &lt;supportedby src="http://validator.w3.org/mobile/" /&gt;
7    &lt;/attribution&gt;

8    &lt;dr&gt;
9      &lt;iriset&gt;
10       &lt;includehosts&gt;example.com&lt;/includehosts&gt;
11     &lt;/iriset&gt;

12     &lt;descriptorset&gt;
13       &lt;typeof src="http://www.w3.org/2008/06/mobileOK#conformant" /&gt;
14       &lt;displaytext&gt;The example.com website conforms to mobileOK&lt;/displaytext&gt;
15       &lt;displayicon src="http://www.w3.org/2005/11/MWI-Icons/mobileOK.png" /&gt;
16     &lt;/descriptorset&gt;
17   &lt;/dr&gt;

18 &lt;/powder&gt;</pre>
</div>

<p>The above example shows a POWDER document which contains information about
who has made the claim, when the claim was made and, in this particular case,
also lists a supporting link to the <a
href="http://validator.w3.org/mobile/">W3C mobileOK Checker</a>. The Checker
is used to test conformance.</p>

<p>Next the DR contains the resources to which this claim applies and the
descriptors. In Semantic Web terms, the <code>typeof</code> element is a
shorthand for <code>rdf:type</code> and asserts that all resources on
example.com are instances of the mobileOK Class. Descriptive text and an icon
are also provided.</p>
<hr />

<h2><a name="Acknowledg" id="Acknowledg">8. Acknowledgements</a></h2>

<p>The editor gratefully acknowledges the substantial contributions made
by:</p>
<dl>
  <dt>Phil Archer - Institute of Informatics &amp; Telecommunications (IIT), NCSR &quot;Demokritos&quot; (formerly with FOSI)</dt>
  <dt>Alan Chuter - Technosite</dt>
  <dt>Diana Pentecost, AOL LLC</dt>
</dl>
<hr />
<!-- REFERENCES -->

<h2><a name="References" id="References">9. References</a></h2>
<dl>
  <dt><a id="dc" name="dc">[DC</a>]</dt>
    <dd><cite><a href="http://dublincore.org/">Dublin Core Metadata
      Initiative</a></cite> This information is at http://dublincore.org/</dd>
  <dt><a id="dr" name="dr">[DR]</a></dt>
    <dd><cite><a href="http://www.ietf.org/rfc/rfc3987.txt">Protocol for Web
      Description Resources (POWDER): Description Resources </a></cite>, P.
      Archer, K. Smith, A. Perego. This document is at
      http://www.w3.org/TR/powder-dr </dd>
  <dt><a id="earl" name="earl">[EARL</a>]</dt>
    <dd><cite><a href="http://www.w3.org/TR/EARL10/">Evaluation and Report
      Language (EARL) 1.0 Schema</a></cite> Schema Document 23 March 2007,
      Shadi Abou-Zahra. This document is at http://www.w3.org/TR/EARL10/</dd>
  <dt><a id="foaf" name="foaf">[FOAF</a>]</dt>
    <dd><cite><a href="http://xmlns.com/foaf/spec/">FOAF Vocabulary
      Specification</a></cite> Namespace Document 24 May 2007, D. Brickley,
      L. Miller. This document is at http://xmlns.com/foaf/spec/ </dd>
  <dt><a id="formal" name="formal">[FORMAL]</a></dt>
    <dd><cite><a href="http://www.w3.org/TR/powder-formal/">Protocol for Web
      Description Resources (POWDER): Formal Semantics</a></cite> 2008, S.
      Konstantopoulos, P. Archer. This document is at
      http://www.w3.org/TR/powder-formal/</dd>
  <dt><a id="grddl" name="grddl">[GRDDL]</a></dt>
    <dd><cite><a href="http://www.w3.org/TR/grddl/">Gleaning Resource
      Descriptions from Dialects of Languages (GRDDL)</a></cite> W3C
      Recommendation 11 September 2007. D. Connolly. This document is at
      http://www.w3.org/TR/grddl/</dd>
  <dt><a id="group" name="group">[GROUP]</a></dt>
    <dd><cite><a href="http://www.w3.org/TR/powder-grouping/">Protocol for
      Web Description Resources (POWDER): Grouping of Resources</a></cite>,
      A. Perego, P. Archer. This document is at
      http://www.w3.org/TR/powder-grouping/</dd>
  <dt><a id="iri" name="iri">[IRI]</a></dt>
    <dd><cite><a href="http://www.ietf.org/rfc/rfc3987.txt">Internationalized
      Resource Identifiers (IRIs)</a></cite>, M. Drst, M. Suignard. IETF,
      January 2005. This document is at
    http://www.ietf.org/rfc/rfc3987.txt</dd>
  <dt><a name="mok" id="mok">[MOK]</a></dt>
    <dd><a href="http://www.w3.org/TR/mobileOK/">W3C mobileOK Scheme 1.0</a>,
      J. Rabin. This document is at http://www.w3.org/TR/mobileOK/</dd>
  <dt><a id="testsuite" name="testsuite">[TESTS]</a></dt>
    <dd><cite><a
      href="http://www.w3.org/TR/powder-test/">Protocol for
      Web Description Resources (POWDER): Test Suite</a></cite> 2008, A.
      Kukurikos. This document is at
      http://www.w3.org/2007/powder/Group/powder-test/</dd>
  <dt><a id="usecases" name="usecases">[USECASES]</a></dt>
    <dd><cite><a href="http://www.w3.org/TR/powder-use-cases/">POWDER: Use
      Cases and Requirements</a></cite> W3C Working Group Note 31 October
      2007, P. Archer. This document is at
      http://www.w3.org/TR/powder-use-cases/</dd>
  <dt><a name="wcag" id="wcag">[WCAG]</a></dt>
    <dd><a href="http://www.w3.org/TR/WCAG20/">Web Content Accessibility
      Guidelines 2.0</a>, B. Caldwell, M. Cooper, L. Guarino Reid, G.
      Vanderheiden. This document is at http://www.w3.org/TR/WCAG20/</dd>
  <dt><a name="xmlsig" id="xmlsig">[XMLSIG]</a></dt>
    <dd><cite><a href="http://www.w3.org/TR/xmldsig-core/">XML-Signature
      Syntax and Processing</a></cite>, Donald. Eastlake, J. Reagle, D. Solo
      (Eds). W3C Recommendation 12 February 2002. this document is at
      http://www.w3.org/TR/xmldsig-core/</dd>
  <dt><a name="wot" id="wot">[WOT]</a></dt>
    <dd><cite><a href="http://xmlns.com/wot/0.1/">Web Of Trust RDF
      Ontology</a></cite>, D. Brickley. This document is at
      http://xmlns.com/wot/0.1/</dd>
  <dt id="xqxp">[XQXP]</dt>
  <dd><cite><a href="http://www.w3.org/TR/xpath-functions/">XQuery 1.0 and XPath 2.0 Functions and Operators</a></cite>, A. Malhotra, J. Melton, N. Walsh. W3C Recommendation, 23 January 2007. This document is at http://www.w3.org/TR/xpath-functions/</dd>

</dl>

<h2 id="change">10. Changes since <a href="http://www.w3.org/TR/2009/NOTE-powder-primer-20090604/">previous version</a> (published 4 June 2009).</h2>
<ul>
  <li><a href="#typo">Typso corrected</a> following e-mail from <a href="http://lists.w3.org/Archives/Public/public-powderwg/2009Jun/0004.html">Paul Denning</a>.</li>
  <li>Media type corrected throughout to say <code>application/powder+xml</code> cf. <code>text/powder.xml</code></li>
</ul>


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