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

19 Sept 2003SSSW Summary Web Services and Semantic Web Services DAML-S WSMF Conclusions

Web Services and Semantic Web Services

19 Sept 2003SSSW 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.

19 Sept 2003SSSW 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). Search Authentication Inter-library loan request Document Translation Payment Digital Library Application Internet

19 Sept 2003SSSW The web service architecture Service Registry Service Requestor Service Provider Find Publish Bind

19 Sept 2003SSSW 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 HTTP SOAP WSDL UDDI WSDL WS-Security WS-Routing etc… BPEL4WS XML

19 Sept 2003SSSW 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 –

19 Sept 2003SSSW 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 –

19 Sept 2003SSSW Towards the Semantic WS Web Service benefit from inclusion of semantics For example, DAML - DARPA Agent Markup Language was designed to provide ontologies and description logics for Agent Markup to improve interoperability Semantic Web provides open, extensible, semantic framework for describing and publishing semantic content Benefits? Improved interoperability Automated service composition, discovery and invocation Access to knowledge on the internet

19 Sept 2003SSSW 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 agreeing whether to transact Invoking  Constructing valid messages based on the published signature/interface of a service Understanding  Interpreting the results of invoking a service Composing Services  Constructing plans to achieve meta-goals based on available Services/Agents

19 Sept 2003SSSW Example of Semantic Mismatch at the Content Level Provider returns value Pennsylvania, but requester only understands 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

DAML-S

19 Sept 2003SSSW 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.

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

19 Sept 2003SSSW Describing the Service Profile A profile represents a functional description of the service 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 searching for, or selecting services  Identify whether the profile description is an instance of existing service categories (profile hierarchy)

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

19 Sept 2003SSSW 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

19 Sept 2003SSSW 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 an atomic process Identify and define the atomic processes  what are its inputs and outputs.  Are there any preconditions that should be met, or effects that are generated? Define the workflow that coordinates the execution of these processes Source: Terry Payne, University of Southampton

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

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

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

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

19 Sept 2003SSSW DAML-S tools Web Service Composer: semi-automatic process for dynamic composition of ws WSDL2DAML-S Converter: complete for Grounding, partial for Profile DAML-S Matchmaker: web service that helps to make connections between service requesters and service providers

WSMF Source: Dieter Fensel (University of Innsbruck)

19 Sept 2003SSSW 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 exchange behaviour and message content Strong mediation Extensive support for bridging data and process differences resulting from strong de-coupling (“compensating strong decoupling”)

19 Sept 2003SSSW Main elements Ontologies Goal/Capability repositories Web Services Mediators

19 Sept 2003SSSW 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

19 Sept 2003SSSW 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 provides service  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 the two cities. One destination city and one origination city. Complete means flight, hotel and car whereby flight is between the two cities and hotel and car are booked in the destination city.

19 Sept 2003SSSW 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 any applicable 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 per night

19 Sept 2003SSSW 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 late arrival, car guaranteed with credit card.  What does “not at all” mean? No flight booked or reserved, no hotel booked or reserved, no car booked or reserved and no financial transaction or obligation existent (or any more, if cancellation fees have been paid)

19 Sept 2003SSSW 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)

19 Sept 2003SSSW 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

Conclusions

19 Sept 2003SSSW 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