The Protocol for Web Description Resources (POWDER) became a W3C Recommendation on the 1st September 2009. This means that it has the same status as well-known standards such as XML and HTML. Quatro Plus provided a major input for its development. This page describes the features of POWDER as they relate to the aims of the Quatro Plus project. It is as non-technical as it can be – however, a level of technical detail is required. For a more general discussion of POWDER, please see the POWDER Primer.

POWDER provides a machine-readable format that specifies:

• the resource or set of resources to which the label applies (as URIs or components of URIs);
• the person or organisation providing the description and possibly other data such as the creation date and period of validity. This enables the automated allegory of the established ‘click to verify’ model used by online trustmarks;
• the description of the resource set;
• references to text and images that give a human readable summary of the description.

The purpose of POWDER is to provide a simple but flexible method for describing groups of web resources, typically "everything on a website." This is in contrast to other metadata formats that describe a single entity at a time.

Why is this important? Let's take an example. At the time of writing, what the end user sees as the MDR Partners home page is actually built up from the HTML page itself plus 19 images, 11 stylesheets, and 3 script libraries. From a computer's point of view therefore 'the MDR Partners Home Page' actually comprises 34 different resources – and that's a single page on a simple website. There are about 50 pages all told on the site plus around 10 other images so even if we just want to describe the text and images, that's around 60 different resources. To apply, say, copyright data to all those resources would normally require "copyright MDR Partners" to be associated with each resource in turn, i.e. 60 copies of essentially the same data. POWDER allows the data to be published once and applied to all the resources in one go.

It is this kind of single description for multiple resources that trustmarks need if they are to be able to say, for example, that "the medical information on website X is accurate and can be trusted" in a way that can be processed by computers.

In order to be able to add trust to the data Quatro Plus identified a core set of criteria common to quality labels that have been incorporated into POWDER itself. These were the basis for a set of terms built into POWDER itself that can be used to assess the trustworthiness of a given description resource (the POWDER term for Quality Label). See Table 1 below.

Table 1: The trust-related terms defined in the POWDER namespace, most of which have their origin in Quatro Plus.

This allows labelling authorities to make statement such as "On 12th July 2009 the ACME Testing Corporation reviewed the Exemplary Company's website and procedures and found them to be in full compliance with our standards. We will stand by this seal of approval until the end of June 2010." That's obviously not the way you'd want to present the information to end users – what they want to see is simply the ACME Testing logo and the words "ACME Testing Approved!" POWDER supports this as shown in Figure 1.

Figure 1: An example of a Quality Label encoded using POWDER.

Lines 4 – 8 are the attribution block. This is where the issue and validity dates are declared along with a link to the description of ACME Testing. Follow the link to "http://acme.example.org/foaf.rdf#acme" and you'd find something like this fragment of RDF:

<foaf:Organization rdf:ID="acme">
  <foaf:homepage rdf:resource="http://acme.example.org/" />
  <foaf:name>The ACME Testing Corporation</foaf:name>
  <authenticate rdf:resource="http://acme.example.org/how_to_authenticate.html" />
  …
</foaf:Organization>

This uses the well-established Friend of A Friend (FOAF) vocabulary to describe the ACME Testing Corporation – other information such as address and phone number would normally be included too. Separating the description of the labelling authority and the labels themselves may seem like an unnecessary complication, however, bear in mind that the labelling authority will issue many labels. By centralising the data we avoid repeating the same data every time a label is issued and substantially ease the task of maintaining it. There is a technical reason for this separation too: POWDER can be processed purely as XML. The labelling authority's description needs to be processed as RDF.

Notice the authenticate element. This is from the POWDER vocabulary and points to a page describing the authentication method(s) that the labelling authority supports. In the case of Quatro Plus, this would describe the access module that the Quatro Proxy would query to authenticate a label. The description of the authentication service might be human-readable or machine readable using a technology such as WSDL.

Lines 10 – 12 of Figure 1 define the scope of the quality label – in this case it is simply 'everything on example.com'. Much more complex definitions are possible so that labels can be applied to specific sections of websites, subdomains or even dynamically generated content (by specifying URL query string components).

Lines 14 – 18 provide the detailed description of the example.com website. For demonstration purposes we've shown a few example from the Quatro vocabulary but it is emphasised that any descriptive vocabulary or combination of vocabularies can be used. For example, Creative Commons licenses, Dublin Core Metadata etc. can all be included just as easily, or indeed instead of, trustmark data.

In our example, the descriptions encode that:

• the content publisher is identified;
• the publisher's privacy policy is declared;
• the content publisher agrees to be bound by the labelling authority's enforcement mechanism;
• the content and/or service meets legal practice in at least Spain;
• the website meets WAI accessibility level AA.

User agents may convey this information to users by displaying the image at http://acme.example.org/logo.png (line 19) and/or displaying the English language text " ACME testing Approved!" (line 20). Alternative language representations may be included for both the image and text.

Youth Panel Example

In the previous section, the descriptors used by the three Youth Panels involved in the project pilots were given as an example of a quality label content. The following is a POWDER version of a quality label created using this vocabuary:

More examples are provided in section 7 of the POWDER Primer.

Where to Store Quality Labels

Once the POWDER DR quality label has been created, it can be stored in the same location as the content being described or on another server or in a database. There is no single 'right' method so labelling authorities are free to choose the most appropriate method for themselves. Ideally, the location of the quality label should be indicated in HTML link elements or the server configured to include an HTTP Link Response Headers pointing to the quality label. A number of the tools supplied by Quatro Plus have their own quality label databases which are set up when the tool is installed (e.g. the Quality Social Network and Label Management Environment tools).