Virtualizing Services and Resources with ProBus: The WS-Policy-Aware Service and Resource Bus
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The document proposes the ProBus approach for virtualizing services and resources with WS-Policy. ProBus uses WS-Policy to enable one-step service/resource selection that decouples providers and consumers. It implements policy-aware message routing and pluggable processors for fine-grained domain-specific policy matching. The approach can be used with WSRF and helps discover suited resources through dynamic policy-based provisioning on SOA infrastructures. Future work aims to integrate ProBus with BPEL for dynamic policy-based workflows and improve fail-over behaviors.
Virtualizing Services and Resources with ProBus: The WS-Policy-Aware Service and Resource Bus
- 1. Virtualizing Services and Resources with ProBus: The WS‐Policy‐Aware Service and Resource Bus Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann Institute of Architecture of Application Systems (IAAS) University of Stuttgart Universitätsstr. 38 70569 Stuttgart Germany tammo.van.lessen@iaas.uni‐stuttgart.de
- 2. The Talk Today Motivation and Introduction Classification of WS‐Policy based Service Selection The ProBus approach for Web Services The ProBus approach for WS‐Resources Architecture & Implementation Conclusions & Outlook © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 2
- 3. Service/Resource Selection Service Registry find publish Service Service Requestor bind Provider WS‐Policy provides a promising approach to Web service/Resource selection based on non‐functional properties. Established approaches are quite cumbersome and not as easy as they could be. We have identified 3 classes of WS‐Policy based service selection. © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 3
- 4. Classes of WS‐Policy based Service Selection Class 1: Manual Service Selection Advantages: Easy to use, no “magic” involved. Disadvantages: inflexible, not really loosely coupled © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 5
- 5. Classes of WS‐Policy based Service Selection Class 2: Policy Based Service Selection Advantages: more flexible Disadvantes: Additional components are needed on client‐side (for “find” and “select”) © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 6
- 6. Classes of WS‐Policy based Service Selection Class 3: The ProBus approach Advantages: easy to use, “make it happen” semantics, more flexibility as the bus is aware of any conversations © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 7
- 7. Sample Request <soap:Envelope ...> <soap:Header> <rb:requiredPolicy> <wsp:Policy> <wsp:ExactlyOne> <wsp:All> <prn:printer prn:maxCostPerPage="$0.3"/> </wsp:All> </wsp:ExactlyOne> </wsp:Policy> </rb:requiredPolicy> </soap:Header> <soap:Body> <!-- Payload of the message --> </soap:Body> </soap:Envelope> © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 8
- 8. Post‐Processing Rules When only the bus takes care of policy matchmaking, it must be aware of domain‐specific details E.g. “There is a match when costPerPage of a printer is less or equal to a given amount” XPath‐based post‐processor <rb:XPathRules rb:assertionQName="prn:printer" ...> <rb:Rule> $reqAssertion/@prn:maxCostPerPage <= $provAssertion/@prn:maxCostPerPage </rb:Rule> <!-- additional rules for this assertion --> </rb:XPathRules> © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 9
- 9. Using ProBus for Dynamic Resource Selection Sample Scenario: Printer Selection © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 10
- 10. How to apply the ProBus approach to WSRF Defining Policies Relating to Resource Properties New WS‐Policy assertion type: resource property condition Resource Property Document <prn:Printer> <prn:waitingQueue>10</prn:waitingQueue> <prn:costPerPage>0.03</prn:costPerPage> <!--other resource properties --> </prn:Printer> <wsp:Policy ...> Request Policy <wsp:ExactlyOne> <wsp:All> <!-- some assertions --> <rb:resourcePropertyCondition rb:type="prn:printer"> <rb:XPath rb:propertyQName="prn:waitingQueue"> number(prn:waitingQueue/text()) <10 </rb:XPath> </rb:resourcePropertyCondition> <!-- more assertions --> </wsp:All> </wsp:ExactlyOne> </wsp:Policy> © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 11
- 11. How to apply the ProBus approach to WSRF Conversations Resources are stateful, hence the EPR is important for subsequent requests Dynamic Resource Management Annotations for factory operations Exception Handling “What happens, if a resource is not available (anymore)?” New fault type: noSuitableResourceFound © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 12
- 12. Architecture and Implementation Implementation based on Apache ServiceMix Policy‐aware message routing Pluggable processors for post‐processing rules Deployment support for policies, post‐processing rules and resource factory descriptors © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 13
- 13. Conclusions and Outlook Conclusions One‐step service/resource selection completely decouples service providers and service consumers XPath‐based post‐processing rules allow for fine‐granular domain‐specific policy matchmaking WS‐Policy can be used in conjunction with WSRF and helps to easily discover suited resources for a particular request Future Work We plan to combine ProBus with a BPEL engine in order to define dynamic policy‐based provisioning workflows on standard based SOA infrastructures We investigate how ProBus can help to achieve better fail‐ over behaviors © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 14
- 14. Thank you for your attention! Any Questions? © Ralph Mietzner, Tammo van Lessen, Alexander Wiese, Matthias Wieland, Dimka Karastoyanova, and Frank Leymann 15
- 15. End of Document