Using context to improve data semantic mediation in web services composition

1. Using context to improve data semantic mediation in web services composition Michaël Mrissa (spokesman) - Philippe Thiran DBDBD’07

2. Outline • Introduction • Web services & composition • Semantic Web services • Mediation challenges • Objectives & contribution • Proposition • Presentation of the context model • Context integration with Web services • General architecture • Mediation & Implementation overview • Conclusion & perspectives

3. Web services & composition • Software components • Interaction model • Composition of Web services • Value-added composite Web services • Objective: answer complex user requests • No semantics yet… • UDDI repositories • WSDL descriptions • SOAP messages Registry Publish Find Travel planning Bind Consumer Provider WS Flight booking Hotel booking Addition

4. Semantic Web services • The Semantic Web • Objectives • Better interoperability between information systems • Automation of information exchange • Means • Explicit machine-interpretable semantic descriptions • Relies on ontologies [Gruber, 1993] • Semantic description of Web Services • Semantic languages • OWL-S [Martin et al., 2004], WSMO [Arroyo and Stollberg, 2004], DIANE [Klein et al., 2005] • Annotation to existing formats • WSDL : SESMA [Peer and Vukovic, 2004], WSDL-S [Miller et al., 2004] • UDDI : [Paolucci and Kawamura, 2002]

5. Mediation challenges • In a composition • Semantic mediation of exchanged data is required • Mediation between (semantic) Web services • IRS-III [Cabral and Domingue, 2005], • WSMX [Mocan et al., 2004] • Agent-based mediation [Williams et al., 2005] • Rule-based approach [Spencer et al., 2004] Travel planning Semantic heterogeneities Output Input Output Input Label conflicts Web Service 1 Web Service 2 PRICE (EUR) PRICE (USD) Unit & value conflicts

6. Objectives & contribution • Multiple goals & constraints • Solve data semantic heterogeneities in a composition • Ease the task of Web services providers • Explicitly describe the semantics of Web services • Enable semantic mediation in composition • Proposition • Use context-based representation of data semantics • Rely on contextual ontologies • Annotate WSDL language with semantics • Detect semantic heterogeneities in the composition • Insert mediation mechanisms at the composition level

7. Outline • Introduction • Web services & composition • Semantic Web services • Mediation challenges • Objectives & contribution • Proposition • Presentation of the context model • Context integration with Web services • General architecture • Mediation & Implementation overview • Conclusion & perspectives

8. Presentation of the context model • Definition of “context” • Collection of semantic assumptions on data interpretation • How should a price be interpreted ? (VAT, currency, scale factor…) • The context model contains 4 elements • Semantic objects • Static modifiers • Dynamic modifiers • Conversion rules & functions • Characteristics of the model • Good integration with WSDL • Based on the MIX model [Bornhövd, 1999] • Definition of static and dynamic modifiers • Semantic conversion between semantic objects

9. Presentation of the context model • A semantic object is a 4-tuple • A concept c defined in a domain ontology • A value v that contains the data itself • A type t that describes the actual type of the value • A context C that characterizes the semantic interpretation of S • C is described as a set of semantic objects • Semantic object in C are called modifiers • Modifiers are dynamic iff: Semantic object S = ( c, v, t, C ) ∀ v ∈ S, ∃ f:{Dom(t) ×...× Dom(t)} → Dom(t) ∧ ∃ {S1, ... Si, ... , Sn }, s.t. Si = <ci, vi, ti, Ci> ∈ Ctxt ∧ Si≠ S ∧ f(v1, ..., vi, ..., vn) = v.

10. Presentation of the context model • A sample semantic object

11. Presentation of the context model • Conversion possibilities between semantic objects • With context conversion functions • Change modifiers’ values • Dynamic aspect • May involve access to remote resources (e.g. currency conversions) • Stored as rules • With type conversion functions • Stored in conversion libraries • Related to the type system (XML Schema) • Semantic comparability • Over a common type and context • Different objects still comparable over limited context

12. Presentation of the context model • Illustration with the travel planning example

13. Context integration with Web services • Semantic annotation of WSDL metamodel

14. Context integration with Web services • Illustration of our annotation • Excerpt of annotated WSDL document • Only static modifiers are added to the description <?xml version=``1.0" encoding=``UTF-8"?> <wsdl:definitions...>... <wsdl:message name=``HotelBookingTicket"> <wsdl:part name=``inputPrice" type=``xsd:double" ctxt:context=``dom1:Price ctxt1:France ctxt1:VATIncluded ctxt1:ScaleFactorOne"/> </wsdl:message>... </wsdl:definitions>

15. Context integration with Web services • Context ontologies • Store context information for each domain concept • Updated by Web services’ providers • Separates top-down and bottom-up aspects

16. Global architecture

17. Mediation & Implementation overview • Prototype • Implementation of the travel planning example • Graphical annotation editor (WSDL4J API) • Development of the mediator

18. Conclusion • A context-based solution for semantic mediation • A model for representing data • Separation of domain and context knowledge • Annotation of Web services’ descriptions • Mediation mechanisms • Future work • How to insert mediators into the composition ? • A first proposal relies on WS-BPEL analysis • A language-independent method ? • This model applies to Web services, but… • What about other semantic tools on the Web ? • Microformats, RDFa… • To what extent the context model applies to the WWW ?

19. Thank you ! Any questions ? University of Namur http://www.fundp.ac.be PRECISE group http://www.fundp.ac.be/precise Contact : • Email addresses • michael.mrissa@fundp.ac.be • pthiran@fundp.ac.be • Authors’ web sites • http://www.fundp.ac.be/~mmrissa/ • http://www.fundp.ac.be/~pthiran/