Web Services and Semantic Web Services: DAML-S and WSMF

1. Web Services and Semantic Web Services: DAML-S and WSMF 21st-26th July 2003 Cercedilla (Spain) Federica Schiappelli Francesco Taglino

2. Summary • Web Services and Semantic Web Services • DAML-S • WSMF • Conclusions SSSW 2003

3. Web Services and Semantic Web Services

4. What is a Web Service? [IBM] • Web was designed primarily for human interpretation and use • Web services are a new breed of Web application • self-describing • modular applications that can be published, located, and invoked across the Web. • Web services perform functions, which can be anything from simple requests to complicated business processes. • In other words, web services are interoperable building blocks for constructing applications. SSSW 2003

5. Web Services: an example • The current web enables • enables users to connect to applications • The web services architecture enables • applications to connect to other applications (from B2C to B2B). Authentication Inter-library loan request Document Translation Search Payment Internet Digital Library Application SSSW 2003

6. Publish Find Bind The web service architecture Service Registry Service Requestor Service Provider SSSW 2003

7. Overview of web services standards • Data and Control Flow description of Web Services; Security and Management • A mechanism for registering and looking up web services • Programmatic way of describing the Web Services Interface • Web Services Communication protocol WS-Security WS-Routing etc… WSDL BPEL4WS UDDI XML WSDL SOAP HTTP SSSW 2003

8. A case of too many proposals? • Many other Web Services Proposals exist: • Transport • DIME – Direct Internet Message Encapsulation • HTTPR – Reliable HTTP • Packaging & Extensions • SOAP-DSIG – SOAP Security Extensions: Digital Signature • SWA–SOAP – Messaging with Attachments • WS-License – Web Services License Language • WS-Referral – Web Services Referral Protocol • WS-Routing – Web Services Routing Protocol • WS-Security – Web Services Security Language Source: Pavel Kulchenko – http://www.xml.com/pub/a/2002/01/09/soap.html?page=1 SSSW 2003

9. A case of too many proposals? • Other Web Services Proposals exist: • Description • BPEL4WS – Business Process Execution Language For Web Services • WSCM – Web Services Component Model • WSFM – Web Services Modeling Framework • WSML – Web Service Meta Language • WSOL – Web Service Offering Language • WSXL – Web Service Experience Language • WSUI – Web Service User Language • XLANG – Web Service Offering Language • Discovery • USML – UDDI Search Markup Language • WS-Inspection – Web Service Inspection Source: Pavel Kulchenko – http://www.xml.com/pub/a/2002/01/09/soap.html?page=1 SSSW 2003

10. Towards the Semantic WS • Web Servicebenefitfrom inclusion of semantics • For example, DAML - DARPA Agent Markup Language wasdesigned to provide ontologies and description logics for AgentMarkup to improve interoperability • Semantic Web provides open, extensible, semantic frameworkfor describing and publishing semantic content • Benefits? • Improved interoperability • Automated service composition, discovery and invocation • Access to knowledge on the internet SSSW 2003

11. Tackling Semantic Interoperability • Semantic Interoperability is a major hurdle for • Locating Services • Different terms used for advertisements and requests • Negotiating contracts & communications • Different protocols used by different communities when agreeingwhether to transact • Invoking • Constructing valid messages based on the publishedsignature/interface of a service • Understanding • Interpreting the results of invoking a service • Composing Services • Constructing plans to achieve meta-goals based on availableServices/Agents SSSW 2003

12. Example of Semantic Mismatch • at the Content Level • Provider returns value Pennsylvania, but requester onlyunderstands two letter state codes (i.e. PA) • at the Attribute level • Requester needs rainfall but provider provides precipitation • at the level of Units of Measure • Requester has value in inches, but provider requires cm • at the Message level • Requester has length & width, provider requires area SSSW 2003

13. DAML-S

14. What is DAML-S? • DAML-S: A DARPA Agent Markup Language for Services • A DAML+OIL ontology for describing properties & capabilities of agents & (Web) services in an unambiguous, computer interpretable mark-up language. SSSW 2003

15. DAML-S Upper Ontology • input types • output types • preconditions • postconditions • communication protocol (RPC, HTTP, …) • port number • serialization • process flow • composition hierarchy • process definitions Source: Terry Payne, University of Southampton SSSW 2003

16. Describing the Service Profile • A profile represents a functional description of theservice capabilities • Describe: • Dataflow properties • Inputs required to invoke the service • Outputs that are generated by the service • World-State properties • Preconditions that should be satisfied • Effects that will be asserted if the service execution is successful • Service metadata is presented • Determine additional data that should be used when searchingfor, or selecting services • Identify whether the profile description is an instance ofexisting service categories (profile hierarchy) SSSW 2003

17. The Service Profile (what it does) Non Functional Properties Functionality Description Source: Terry Payne, University of Southampton SSSW 2003

18. The Profile properties • Non Functional • Provide supporting information about services (i.e., serviceName, textDescription, …) • Functional • Functional specification of what the service provides in terms of parameters • Preconditions: set of conditions that should hold prior to service invocation (i.e., Credit Card is valid) • Inputs: set of necessary inputs that the equester should provide to invoke the service (i.e., Credit Card number) • Outputs: results that the requester should expect after interaction with the service provider is completed (i.e., Flight booking number) • Effects: set of statements that should hold true if the service is invoked successfully (i.e., Credit Card being debited) Source: Terry Payne, University of Southampton SSSW 2003

19. Decribing the Service Process Model • A process model represents a service as a workflow,consisting of several processes • Each process could itself be another service, a workflow, or anatomic process • Identify and define the atomic processes • what are its inputs and outputs. • Are there any preconditions that should be met, or effects that aregenerated? • Define the workflow that coordinates the execution of theseprocesses Source: Terry Payne, University of Southampton SSSW 2003

20. The Service Process Model (how it works) Source: Terry Payne, University of Southampton SSSW 2003

21. Describing the Service Grounding • Provide a WSDL file for the service being described • Identify and map • The atomic processes within the process model to thecorresponding operations in the WSDL description • The inputs & outputs correspond to WSDL messages Source: Terry Payne, University of Southampton SSSW 2003

22. The Service Grounding (how to access it) Source: Terry Payne, University of Southampton SSSW 2003

23. Publication Profile Discovery Simulation Selection Process Model Verification Composition Invocation, Interoperation Grounding Monitoring, Recovery Development … Deployment … Use … Source: David Martin for DAML-S Coalition SSSW 2003

24. DAML-S tools • Web Service Composer: semi-automatic process for dynamic composition of ws http://www.mindswap.org/~evren/composer/ • WSDL2DAML-S Converter: complete for Grounding, partial for Profile http://www.daml.ri.cmu.edu/wsdl2damls • DAML-S Matchmaker: web service that helps to make connections between service requesters and service providershttp://www.damlsmm.ri.cmu.edu/ SSSW 2003

25. WSMF Source: Dieter Fensel (University of Innsbruck)

26. What is the WSMF • WSMF: Web Services Modeling Framework provides a framework for peer-to-peer communication between any number of endpoints (i.e., anything that can be invoked and responds) • Strong de-coupling • Each endpoint is fully autonomous in its message exchangebehaviour and message content • Strong mediation • Extensive support for bridging data and process differencesresulting from strong de-coupling (“compensating strong decoupling”) SSSW 2003

27. Main elements • Ontologies • Goal/Capability repositories • Web Services • Mediators SSSW 2003

28. Ontologies • Definition in context of basic communication elements • Document types • Structure of data communicated • Semantics • Meaning of data communicated • Both are defined by endpoints due to their autonomy • Definition in context of WSMF • Goal and pre-/post-condition support • Meaning of goal web service provider addresses • Meaning of goal web service client has in mind • This is defined by endpoints due to their autonomy SSSW 2003

29. Capability Repositories • Capability • Client can state goal it has, i. e. what it tries to accomplish • E. g. “book a complete round-trip travel” • Endpoint can state goal it addresses, i. e. for what goal it providesservice • E. g. “book most expensive hotels” • E. g. “book affordable hotels” :-) • Ontology • E. g. definition of round-trip travel • Trip between two cities whereby transportation is between thetwo cities. One destination city and one origination city.Complete means flight, hotel and car whereby flight is betweenthe two cities and hotel and car are booked in the destinationcity. SSSW 2003

30. Capability Repositories (2) • Pre-conditions • Input that web service requires to function properly • E. g. definition of “affordable” or “most expensive” • Ontology • What does “affordable” mean? • Total charge per night per room (including taxes and anyapplicable fees) is in the range of USD 49 to USD 99 • “Most expensive” is clear :-) • Select the hotel in the city with the highest price per room pernight SSSW 2003

31. Capability Repositories (3) • Post-condition • Output web service provides • E. g. a complete trip is booked or not at all • Ontology • What does “booked” mean? • Flight in status OK, hotel guaranteed with credit card for latearrival, car guaranteed with credit card. • What does “not at all” mean? • No flight booked or reserved, no hotel booked or reserved, nocar booked or reserved and no financial transaction orobligation existent (or any more, if cancellation fees have beenpaid) SSSW 2003

32. Web Services definition • Name • Reference to goal and pre/post cond. • Input/Output data • Data flow (i.e., split, join, typecast) • Control flow (i.e., sequence, conditional branching, for/while-loops, parallel exec.) • Compensation (i.e., undoing, side effects) SSSW 2003

33. Mediation • Data Mediation • Data matching (lossless transf.) • Data mismatching (lossy transf.) • Data-overcomplete mismatch • Data-incomplete mismatch • Semantic mismatches • Process Mediation • Precise match • Message sent by sender is expected by receiver • Unresolvable mismatch • Message sent by sender are not expected by receiver • If message cannot be consumed, merger, re-arranged or artificially produced • Resolvable mismatch SSSW 2003

34. Conclusions

35. Conclusions • DAML-S is an ontology for describing properties & capabilities of Web services • WSMF: defines description elements for • adding semantics to WS • providing WS as a scalable infrastructure for eWork and eCommerce • They are complementary • DAML-S could be used for defining a formal semantics but • it lacks many of the modeling primitives important within WSMF • it does not provide formal semantics for many of the primitives expressed in it SSSW 2003