POWDER: Use Cases and Requirements

W3C Working Group Note 25 May 2007

This version:
Latest version:
Phil Archer, Family Online Safety Institute


This document sets out the use cases and requirements that have motivated the development of the Protocol for Web Description Resources (POWDER). The use cases address social and commercial needs to provide information about groups of Web resources, such as those available from a Web site, to aid the annotation and/or personalization of content for end users in varying delivery contexts.

Status of this document

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 W3C technical reports index at http://www.w3.org/TR/.

This is a W3C Working Group Note of the POWDER Use Cases and Requirements, developed by the POWDER Working Group as part of the Semantic Web Activity, to aid public discussion and solicit feedback on the group's aims. The group is particularly keen to learn of other potential use cases or additional features that should be considered for POWDER.

Please send comments about this document to public-powderwg@w3.org (with public archive) by 8 July 2007, after which a revised version will be published to reflect the feedback received.

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.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures 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 Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

1 Introduction

The development of the Protocol for Web Description Resources has been motivated by both commercial and social concerns. On the social side, there is a demand for a system to identify content that meets certain criteria as they apply to specified audiences. Commercially, there is a demand to be able to personalize content for a particular user or delivery context.

POWDER will address these demands by defining a method through which relatively small amounts of metadata, that can be produced quickly and easily, can be applied to large amounts of content.

The use cases and requirements for POWDER were originally developed under the Web Content Label Incubator Activity. They have been revised and updated for this Working Group Note.

2 Use cases

2.1 Profile matching

The generic use case for profile matching is that a user receives content suited to their delivery context; that is, the combination of user preferences, device capabilities and current state at the time of content delivery. Description Resources facilitate this decision by making available rules about groups of Web resources to a Web server. At request time the Web Server can determine if there are any rules in the DR which apply to the requested URI, and respond to the User accordingly.

This extended use case refers to the following terms.


User: A human who perceives and interacts with the Web.

Device: Apparatus through which a user can perceive and interact with the Web

Server: The role adopted by an application when it is supplying resources or resource manifestations.

Network Operator: A mobile telephony and data infrastructure provider.

Adaptation: a process of selection, generation or modification of Web content to suit the given delivery context.

Content Types:

Web content: any resource retrievable via a URI over the World Wide Web intended for direct user consumption (Web pages and audio/visual media types).

2.1.1 Generic Profile Matching Use Case

Step 1
User requests Web content via their device.
Step 2
A Server resolves the URI and determines that there is metadata associated with the resource that asserts access conditions.
Step 3
The Server matches the URI-applicable assertions in the metadata, to the user's delivery context.

Then either

Step 4a
The Server interprets that there are no constraints on the user accessing the content,
Step 5a
The Server responds to the User with the full Web content.


Step 4b
The metadata asserts that the requested URI is not appropriate to the current delivery context.
Step 5b
The Server adapts the content and responds to the User.

2.1.2 Adaptive Search Results

  1. Anne enters a search string, 'Pianos', into a search engine, search.example.org.
  2. The search engine notes the characteristics of Anne's device by retrieving a description from a Device Description Repository.
  3. The search engine obtains a set of URIs that are relevant to the search key.
  4. The search engine notes the characteristics of the content associated with each URI.
  5. The search engine compares the device characteristics to the content characteristics.
  6. The search engine removes the URIs of content that cannot be rendered by, or adapted to, Anne's device.
  7. The search engine returns a list of the remaining URIs to Anne.
  8. If Anne selects from one of the returned URIs, the identified content is delivered as is (if appropriate to the known device capabilities) or adapted accordingly.

2.1.3 mobileOK

  1. Dan wants to be able to access a directory of Web sites that will give an optimal user experience on his mobile phone. He enters 'Sausages' into search.example.mobi and checks the box that says 'MobileOK results only' [MOK]
  2. The search engine retrieves a set of URIs from its index and determines those resources with associated metadata describing their characteristics. Any resources without such metadata are discarded.
  3. The search engine inspects the metadata and determines which resources are declared to be conformant with mobileOK.
  4. The search engine returns a list of the URIs of mobileOK conformant resources to Dan.
  5. If Dan selects from one of the returned URIs, the identified content is delivered as is.

2.1.4 Functional User Experience

  1. Hwang visits a martial arts Web site through his laptop computer and requests a page of streaming video clips.
  2. The Server's content management system detects that there is metadata associated with all URIs containing /video/ in their path.
  3. The Server retrieves and inspects the metadata and discovers that only devices connecting at a minimum bandwidth of 150K will be able to stream the videos.
  4. The Server determines that Hwang's laptop is currently connected at a lower bandwidth.
  5. The Server redirects Hwang to a page of images more appropriate to his bandwidth.

2.1.5 Web Accessibility

  1. Iris, who has limited dexterity and therefore difficulty using a mouse, wishes to shop for CDs online. A helpful Web search engine allows her to set a preference for web pages that can easily be used with keyboard-only input. She searches for her favorite artist through the Search engine's 'search shops' interface.
  2. The Search engine retrieves a set of URIs from its index, and fetches metadata assertions from a database provided by a trusted third party.
  3. The Server inspects the metadata and looks for any assertions made about Web accessibility, especially keyboard operability.
  4. The Server returns the conformant results and Iris goes shopping.

2.1.6 Child Protection

  1. Barry, who is 16 years old, has been sent a URI in an SMS message to his mobile phone. He clicks on the link, which unknown to him, is to an adults-only area of a example.mobi.
  2. The Network Operator has a child protection policy which allows parents to decide if they or their family can access certain content. One technique it uses is to check any metadata references before responding to the User.
  3. The Network Operator retrieves a metadata description from the Web portal, which declares that anything at the server adult.example.mobi contains explicit nudity. The Network Operator determines from Barry's profile that his parents have asked such access to be restricted.
  4. The Network Operator returns a Child Protection explanation page to Barry.

2.1.7 Privileged Content

  1. Ray is a premium customer of exampleISP, an Internet Service Provider. They have a deal which allows him to access premium content on other Web sites as long as he accesses it using exampleISP. Ray visits such a 3rd party, games.example.org
  2. The games.example.org Server retrieves metadata which describes the group of resources reachable from their homepage.
  3. The Server determines from the metadata assertions that all files whose suffix is .jad (to indicate a Java download) are for premium users. The Server determines from Ray's delivery context that he is a premium customer of exampleISP
  4. The Server responds with a page containing all links, available for Ray to download.

Motivates: 3.1.1 Making Assertions; 3.1.2 The Role of a Description Resource; 3.1.3 Grouping; 3.1.4 Composite Assertions; 3.1.9 Standard Vocabularies; 3.1.10 Identity; 3.1.11 Unambiguous; 3.2.1 Authentication; 3.2.2 Separation of Description and Resource; 3.3.1 Machine-Readable; 3.3.2 Formal Grammar; 3.3.4 Compact.

2.2 Trustmarks

There are several possible models in which assertions and claims can be made, authenticated and reported to the end user. Each of the following has several elements in common but differs in details such as whether it is the content provider or the trust mark operator that makes the original claim, whether the data is stored on the trust mark operator's servers or alongside the content itself, and whether the trust mark operator provides the description or the authentication for a description.

2.2.1 Browser Display

Joseph installs a web browser plugin on his personal computer designed to aggregate and interpret safety/reliability information about Web sites from various sources, such as reputation and accreditation services. The web browser plugin provides a visual indication of whether the Web site that Joseph is currently visiting is considered trustworthy or not.

The plugin retrieves information about Web sites using several methods. One of these methods involves querying the Description Resource associated with a Web site.

Diagrammatic representation of Use case 2.2.1 (Trust Mark)

Diagrammatic representation of Use case 2.2.1 (Trust Mark)

Joseph visits a Web site to do some holiday shopping. The browser plugin identifies the site's Description Resource, which asserts that the Web site has been certified by an accreditation service and provided with a trustmark.

The plugin determines that the accreditation and trustmark are provided by a known entity with a validation mechanism in place. The plugin queries the accreditation service provider by submitting the assertion of the Web site's accreditation.

The accreditation service provider validates the assertion of accreditation and provides a graphic file containing a trustmark. The plugin displays the trustmark to Joseph along with a visual indication that the Web site has a good reputation.

2.2.2 Compliance Monitoring

This use case refers to the following terms.

Evaluates Web content and if it complies with rules, issues a label to the Web site owner.
A body that oversees quality and accessibility of Web content. Needs to be able to read labels published by Web sites.
An automated system used by the Regulator to read labels on Web sites.
Authentication Service
A Web service that attests to the validity and authenticity of labels. Must be able to read the labels used by Evaluators.
Report generator
An application that collates and summarizes compliance information provided by the Robot in a form suitable for human users employed by the Regulator.

A government department (regulator) is responsible for overseeing the accessibility of all Web sites produced by different levels of government: national and local. It has approved a number of private-sector companies to carry out accessibility evaluation work but there is a need for some mechanism for the evaluators to label the sites in a reliable and machine-readable way, to allow automated monitoring.

The evaluators provide Web sites with labels. Web site administrators embed links to the labels in their pages. A robot used by the government department regularly crawls the Web sites and reads the labels, and checks the data for authenticity and validity using a web service provided by a third-party Authentication Service. A report generator produces progress reports and violation notices based on the information from the data.

2.2.3 Direct Data Provision

The Example Trustmark Scheme reviews online traders, providing a trustmark for those that meet a set of published criteria. The scheme operator wishes to make its trustmark available as machine-readable code as well as a graphic so that content aggregators, search engines and end-user tools can recognize and process them in some way.

The trustmark operator maintains a database of sites it has approved and makes this available in two ways:

Firstly, the trusted site includes a link to the database. A user agent visiting the site detects and follows the link to the trustmark scheme's database from which it can extract the description of the particular site in real time.

Secondly, the scheme operator makes the full database available in a single file for download and processing offline.

Since the actual data comes directly from the trustmark scheme operator, it is not open to corruption by the online trader and can therefore be considered trustworthy to a large degree. To reduce the risk of spoofing, however, the data is digitally signed.

2.2.4 Description Authentication

Mrs. Bryanton teaches 8 year olds at her local school. An IT enthusiast, she makes her teaching materials available through her personal Web site. She adds a Description Resource to her material that declares the subject matter and curriculum area.

In order to gain wider trust in her work she submits her site for review by her local education authority. That body then publishes its own Description Resource that declares Mrs Bryanton's Description Resource to be accurate.

Motivates: 3.1.1 Making Assertions; 3.1.2 The Role of a Description Resource; 3.1.3 Grouping; 3.1.4 Composite Assertions; 3.1.5 Multiple DRs; 3.1.6 Independence; 3.1.7 Attribution; 3.1.8 Reference; 3.1.9 Standard Vocabularies; 3.1.10 Identity; 3.1.11 Unambiguous; 3.2.1 Authentication; 3.2.2 Separation of Description and Resource; 3.2.4 Link to Test Results; 3.2.5 Bulk Data Transfer; 3.3.1 Machine-Readable; 3.3.2 Formal Grammar; 3.3.3 Human Readable; 3.3.4 Compact; 3.3.5 Images.

2.3 Rich Metadata for RSS/ATOM

Dave Cook's Web site offers reviews of children's films and the site is summarized in both RSS and ATOM feeds. Most of the films reviewed have an MPAA rating of G and/or British Board of Film Classification rating of U. This is declared in a rating for the channel as a whole. However, Dave includes reviews of some films rated PG-13 or 12 respectively which is declared at the item level and overrides the channel level metadata.

The actual rating information comes from an online service operated by the relevant film classification board itself and is identified using a URI and human-readable text. The movie itself is identified by either an ISAN number or the relevant Internet Movie Database entry ID number. Trust is implicit given the source of the data, which is indicated by a link to Dave's site's policy.

Separately, Fred combines Dave Cook's and other review feeds to provide alternative reviews of the movies by transforming the ATOM feeds into RDF and creating an aggregate view using SPARQL queries.

Motivates: 3.1.1 Making Assertions; 3.1.2 The Role of a Description Resource; 3.1.3 Grouping; 3.1.5 Multiple DRs; 3.1.6 Independence; 3.1.7 Attribution; 3.1.9 Standard Vocabularies; 3.1.10 Identity; 3.1.11 Unambiguous; 3.2.1 Authentication; 3.2.2 Separation of Description and Resource; 3.2.3 Default Description; 3.3.1 Machine-Readable; 3.3.2 Formal Grammar; 3.3.3 Human Readable; 3.3.4 Compact.

2.4 Expressing Opinions

These two use cases are slight variations on a common theme. The important difference between them being that in the first case, the description is made using only explicit semantics. In the second, user-defined tags (i.e. free text) are used but these are then associated with a semantically explicit description. In both cases, the opinions expressed are relatively complex so that the semantics are critical. Furthermore, these are also scenarios where there is unlikely to be any relationship between the content provider and the individual describing the content.

2.4.1 An Explicit Viewpoint

Fred operates an antiracism education site which aggregates and curates content from around the Web. Fred wants to label the resources that he aggregates such that educational and other institutions may harvest the resources and associated commentary and metadata automatically for reuse within their instructional support systems, etc.

One of the ways in which Fred wants to curate resources is to say about them that they are pedagogically useful but politically noxious. For example, some sites on the Web make claims about Martin Luther King, Jr that are motivated by a racist ideology and are historically indefensible. Fred's vocabulary allows him to claim that such resources are pedagogically useful for purposes of analysis, but that they are otherwise suspicious and should only be consumed by students in an age-appropriate manner or with appropriate supervision, etc. In other words, Fred needs to be able to make sharply divergent claims about resources: (1) that they are noteworthy, and (2) that they are, from his perspective, dangerous or noxious or troublesome.

2.4.2 User-Defined Tags

The social book-marking site tags.r.us allows their users to tag any resource and so provides a service through which people can annotate both their own and others' resources.

Anders, a tags.r.us, user, finds a website that he considers racist, however relevant to his study of racist ideology. He tags the site with his own keywords: "racism project", "modern" and "example."

To enable such user-defined tags to be shared with others who are likely to use slightly different terms, tags.r.us allows users to assign a link between their own tags and a Description Resource. An agent can thus use the tag as appropriate, processing the explicit semantics provided by the DR but perhaps presenting other users with Anders' original tags.

Diagrammatic representation of Use case 2.4.2 (User Defined Tags)

Diagrammatic representation of Use case 2.4.2 (User Defined Tags)

Motivates: 3.1.1 Making Assertions; 3.1.2 The Role of a Description Resource; 3.1.3 Grouping; 3.1.5 Multiple DRs; 3.1.6 Independence; 3.1.7 Attribution; 3.1.8 Reference; 3.1.9 Standard Vocabularies; 3.1.10 Identity; 3.1.11 Unambiguous; 3.2.1 Authentication; 3.2.2 Separation of Description and Resource; 3.2.5 Bulk Data Transfer; 3.3.1 Machine-Readable; 3.3.2 Formal Grammar; 3.3.3 Human Readable; 3.3.6 User-Generated Tags.

2.5 Scalar Classification

A company named Advance Medical Inc. reviews medical literature on the Web based on a range of quality criteria such as the qualifications of the author(s), the methodology used and the research evidence presented. The criteria may be changed according to current scientific and professional developments. The review process leads to medical literature being classified in two ways:

Quality of Content
Level A: Excellent
Level B: Good
Level C: Acceptable

Peer Review
Level A: Content has been subjected to peer review
Level B: Content has not been subject to peer review

The Quality of Content classification is scalar. i.e. meeting the criteria for Level A implies also meeting Level B which in turn implies meeting Level C. In contrast, meeting Level A for Peer Review does not imply meeting Level B.

The company produces data that declares the classification levels and provides a summary of each document it has reviewed. The data is stored in a metadata repository which can be accessed via the Web.

M.D. Smith uses the data in the repository to make decisions about heath care for specific clinical circumstances.

Motivates: 3.1.1 Making Assertions; 3.1.2 The Role of a Description Resource; 3.1.3 Grouping; 3.1.4 Composite Assertions; 3.1.5 Multiple DRs; 3.1.6 Independence; 3.1.7 Attribution; 3.1.9 Standard Vocabularies; 3.1.10 Identity; 3.1.11 Unambiguous; 3.2.1 Authentication; 3.2.2 Separation of Description and Resource; 3.2.4 Link to Test Results; 3.2.5 Bulk Data Transfer; 3.3.1 Machine-Readable; 3.3.2 Formal Grammar; 3.3.3 Human Readable; 3.3.5 Images

2.6 Expressing Editorial Policy

VLCC, (the Very Large Content Company) offers millions of items of content which are delivered through a variety of branded channels. Its strict editorial policies dictate that before publication, all content is reviewed by a member of the editorial team who checks for compliance with those policies. This is encoded in a description covering all its brands that states "VLCC works to ensure that all its content meets W3C Web Accessibility Initiative level AA and is suitable for all audiences unless otherwise stated. If you find any of our content does not meet these standards, please contact us."

The editor is responsible for adding two further descriptions:

  1. Key words (tags). For example: "News, Middle East", "Lifestyle, DIY, Decorating", "Entertainment, Celebrity Gossip."
  2. An age-rating, taken from a set of pre-defined options. For example, content delivered through VLCC's 'Youth of Today' brand is usually suitable for all ages, however, occasionally, content aimed at young adults is published that might be inappropriate for younger children and is described by one of the other available ratings in line with the overall editorial policy.

Motivates: 3.1.1 Making Assertions; 3.1.2 The Role of a Description Resource; 3.1.3 Grouping; 3.1.4 Composite Assertions; 3.1.5 Multiple DRs; 3.1.7 Attribution; 3.1.8 Reference; 3.1.9 Standard Vocabularies; 3.1.10 Identity; 3.1.11 Unambiguous; 3.2.1 Authentication; 3.2.2 Separation of Description and Resource; 3.2.3 Default Description; 3.2.4 Link to Test Results; 3.3.1 Machine-Readable; 3.3.2 Formal Grammar; 3.3.3 Human Readable; 3.3.6 User-Generated Tags.

3 Requirements

The following requirements are derived from the preceding use cases. They have been assigned to thematic groups as an aid to readability.

3.1 Fundamentals

3.1.1 Making Assertions

It must be possible for both resource creators and third parties to make assertions about information resources.

3.1.2 The Role of a Description Resource

A Description Resource, DR, must be able to describe aspects of a group of information resources using terms chosen from different vocabularies. Such vocabularies might include, but are not limited to, those that describe a resource's subject matter, its suitability for children, its conformance with accessibility guidelines and/or Mobile Web Best Practice, its scientific accuracy and the editorial policy applied to its creation.

3.1.3 Grouping

It must be possible to define sets of resources and have DRs refer to those sets. For example, DRs can refer to all the pages of a Web site, defined sections of a Web site, or all resources on multiple Web sites.

3.1.4 Composite Assertions

DRs must support a single composite assertion taking the place of a number of other assertions. For example, WAI AAA can be defined as WAI AA [WAI] plus a series of detailed descriptors. Other examples include mobileOK and age-based classifications from a named authority.

3.1.5 Multiple DRs

It must be possible for more than one DR to refer to the same resource or group of resources.

Furthermore, it must be possible for a resource to refer to one or more DRs. It follows that there must be a linking mechanism between content and descriptions.

3.1.6 Independence

DRs must be able to point to any resource(s) independently of those resources.

3.1.7 Attribution

A DR must include assertions about itself using appropriate vocabularies. As a minimum, a DR must have data describing who created it. Good practice would be to declare its period of validity, how to provide feedback about it, who last verified it and when etc.

3.1.8 Reference

It must be possible for a DR to refer to other DRs.

3.1.9 Standard Vocabularies

There must be standard vocabularies for assertions about DRs.

3.1.10 Identity

DRs, their components and individual assertions should have unique and unambiguous identifiers.

3.1.11 Unambiguous

Assertions within DRs should be made using descriptors that themselves have unique identifiers.

3.2 Fitting in with Commercial or Other Large Scale Workflows

3.2.1 Authentication

It must be possible for DRs to be authenticated.

3.2.2 Separation of Description and Resource

It must be possible to create and edit DRs without modifying the resources they describe

3.2.3 Default Description

It must be possible to identify a default DR for a group of resources and provide an override at specific locations within the scope of the DR.

3.2.4 Link to Test Results

It must be possible to link DRs with specific test results that support the claims made.

3.2.5 Bulk Data Transfer

It must be possible for a data provider to make its repository of Description Resources available as a bulk download.

3.3 DRs for Humans and Machines

3.3.1 Machine-Readable

It must be possible to express DRs in a machine-readable way.

3.3.2 Formal Grammar

The machine-readable form of a DR must be defined by a formal grammar.

3.3.3 Human Readable

DRs must provide support for a human readable summary of the claims it contains.

3.3.4 Compact

It must be possible to express DRs in a compact form.

3.3.5 Images

It must be possible to associate DRs with images.

3.3.6 User-Generated Tags

It must be possible to encode user-generated tags in DRs.

4 Acknowledgements

The editor acknowledges the contributions of members of the POWDER WG and the WCL-XG in compiling this document. In particular Dan Appelquist, Dave Rooks, Pantelis Nasikas, Kjetil Kjernsmo, Kai-Dietrich Scheppe, Kendall Clark, Jo Rabin, Kevin Smith, Alan Chuter and Zeph Harben.

5 References

MobileOK is a trustmark that can be applied to online content that meets criteria derived from the Mobile Web Best Practices
WAI Conformance is defined in the W3C Web Content Accessibility Guidelines