Overview: W3C Workshop on Constraints and Capabilities for Web Services

Workshop Goal: "Various aspects of a Web service may require description. This includes its constraints (e.g., 'You must use HTTP Authentication when accessing this service') and its capabilities (e.g., 'I can support GZIP compression'). Likewise, clients accessing Web services have constraints and capabilities of their own to consider when accessing services.

Many such aspects are typically associated with a number of orthogonal problem domains; for example, it may be desirable to describe constraints and capabilities (also, 'policy') regarding security, reliable messaging and message serialization for a particular endpoint. A domain-neutral means of expressing the relationships between policies (e.g., 'You MUST use HTTP Authentication and MAY use GZIP compression') would allow a particular aspect to be defined without reference to other domains.

Additionally, Web services provide a number of means of associating metadata (and, therefore, constraints and capabilities) with services; for example, WSDL, UDDI, HTTP and SOAP headers all might allow association of such information with a particular service. It would be advantageous to abstract the association of such metadata with a Web service from its expression, to avoid duplication of effort and allow new association mechanisms to be easily defined.

This Workshop is being held to discuss the establishment of a framework for the expression of such constraints and capabilities and their association with Web services, in order to promote their interoperability and scalability. It is expected that discussion at the Workshop will lead to a common understanding of the problem space and provide recommendations to the W3C regarding further work..."

Topics for position papers: Topics may include, but are not limited to:

• Relationship to existing effort(s), with exploration of benefits and drawbacks to leveraging them
• Specific problem domains: e.g., security, privacy, reliable messaging, internationalization
• Policy Model and the Web Services Architecture: machine readable constraints on the allowable actions or states of an agent
• Processing models for constraints and capabilities on requester and provider agents
• Negotiation and advertising: patterns for policy interaction
• Content models for policy: sequence/array/choice, */+/once
• Obligations associated with constraints: must, may, may not, must not
• Policy management: merging, delegation, cancel, request, revocation, priorities, preferences, meta-policies
• Abstract vs. concrete constraints and capabilities
• Intermediaries and policy
• Communicating policy decisions to other parties
• Scoping of policies across interactions, in time, and/or scoping of policy decisions
• Policy subjects and identity: what are constraints and capabilities applied to?
• Aligning existing and future policy vocabulary semantics and syntax

Organizing Committee

• Program Chairs: Mark Nottingham (BEA), Philippe Le Hégaret (W3C)

• Program Committee Members:

  • Anne Anderson (Sun)
  • David Booth (W3C)
  • Glen Daniels (Sonic)
  • Jim Hendler (Maryland Information and Network Dynamics Lab at the University of Maryland)
  • Maryann Hondo (IBM)
  • Amelia Lewis (TIBCO)
  • Greg Pavlik (Oracle)
  • Claus von Riegen (SAP)
  • Steve Ross-Talbot (Enigmatec)
  • Jeffrey Schlimmer (Microsoft)

Related Topics

The W3C Workshop organizers have clarified that discussion is welcome on the relationship of related topics to the central Workshop theme of Web Services constraints and capabilities. Some related topics include:

• WSDL extensibility / features and properties

• WS-Policy Framework and Attachment specifications

• SOAP's abstract model, SOAP modules, features and properties

• The Semantic Web: OWL-S, Rei, Ontologies for Web services

• Rule languages: RuleML

• Web Content Negotiation and Composite Capabilities/Preference Profile (CC/PP)

• Platform for Privacy Preferences (P3P)

• Enterprise Privacy Authorization Language (EPAL)

• HTTP headers and other Web-based policies; e.g., robots.txt, WebDAV properties

• "Extensible Access Control Markup Language (XACML)"

• Web Services Policy Language (WSPL); see the Sun reference page and local references

• IETF Policy Framework

• The boundary and interactions between policy, service level agreements, and business level agreements in web services.

Principal References

• W3C Workshop on Constraints and Capabilities for Web Services. October 12-13, 2004. Oracle Conference Center, Redwood Shores, CA, USA.
• Contact address for position papers: team-ws-cc-submissions@w3.org
• Workshop Chairs: Mark Nottingham and and Philippe Le Hégaret
• W3C Workshops
• W3C Workshop news item
• W3C Web Services Activity
• Web Services Activity Statement
• W3C Architecture Domain