1 University of Namur, Belgium PReCISE Research Center Using context to improve data semantic mediation in web services composition Michaël Mrissa (spokesman) - Philippe Thiran DBDBD07

2 University of Namur, Belgium PReCISE Research Center 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 University of Namur, Belgium PReCISE Research Center Web services & composition Software components Interaction model Composition of Web services Value-added composite Web services Objective: answer complex user requests No semantics yet… Consumer Registry Provider Bind Publish Find WS UDDI repositories WSDL descriptions SOAP messages Travel planning Flight booking Hotel booking Addition

4 University of Namur, Belgium PReCISE Research Center 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 University of Namur, Belgium PReCISE Research Center Travel planning 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] Input Output PRICE (USD) Input Output Label conflicts Unit & value conflicts Semantic heterogeneities Web Service 1 Web Service 2 PRICE (EUR)

6 University of Namur, Belgium PReCISE Research Center 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 University of Namur, Belgium PReCISE Research Center 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 University of Namur, Belgium PReCISE Research Center 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 University of Namur, Belgium PReCISE Research Center 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) {S 1,... S i,..., S n }, s.t. S i = Ctxt S i S f(v 1,..., v i,..., v n ) = v.

10 University of Namur, Belgium PReCISE Research Center Presentation of the context model A sample semantic object

11 University of Namur, Belgium PReCISE Research Center 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 University of Namur, Belgium PReCISE Research Center Presentation of the context model Illustration with the travel planning example

13 University of Namur, Belgium PReCISE Research Center Context integration with Web services Semantic annotation of WSDL metamodel

14 University of Namur, Belgium PReCISE Research Center Context integration with Web services Illustration of our annotation Excerpt of annotated WSDL document Only static modifiers are added to the description... <wsdl:part name=``inputPrice" type=``xsd:double" ctxt:context=``dom1:Price ctxt1:France ctxt1:VATIncluded ctxt1:ScaleFactorOne"/>...

15 University of Namur, Belgium PReCISE Research Center 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 University of Namur, Belgium PReCISE Research Center Global architecture

17 University of Namur, Belgium PReCISE Research Center Mediation & Implementation overview Prototype Implementation of the travel planning example Graphical annotation editor (WSDL4J API) Development of the mediator

18 University of Namur, Belgium PReCISE Research Center 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 University of Namur, Belgium PReCISE Research Center Contact : addresses Authors web sites Thank you ! Any questions ? University of Namur PRECISE group University of Namur PRECISE group