using context to improve data semantic mediation in web services composition

1

University of Namur, BelgiumPReCISE Research Center

Using context to improve data semantic mediation in web services compositionUsing context to improve data semantic mediation in web services composition

Michaël Mrissa (spokesman) - Philippe Thiran DBDBD’07Michaël 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…

Consumer

Registry

ProviderBind

PublishFind

WS

• UDDI repositories• WSDL descriptions• SOAP messages

Travel planning

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


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 OutputLabel conflicts

Unit & value conflicts

Semantic heterogeneities

WebService 1

WebService 2

PRICE (EUR)

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



• 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. Si = <c

i, v

i, t

i, C

i> Ctxt S∈ ∧

i ≠ S f(v∧

1, ..., v

i, ..., v

n) = v.

10



• A sample semantic object

11



• 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



• Illustration with the travel planning example

13


Context integration with Web services

• Semantic annotation of WSDL metamodel

14



• 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 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


Contact :

• Email addresses

• [email protected]

• [email protected]

• Authors’ web sites

• http://www.fundp.ac.be/~mmrissa/

• http://www.fundp.ac.be/~pthiran/

Thank you !Thank you !

Any questions ?Any questions ?

University of Namur

http://www.fundp.ac.be

PRECISE group

http://www.fundp.ac.be/precise

University of Namur

http://www.fundp.ac.be

PRECISE group

http://www.fundp.ac.be/precise

using context to improve data semantic mediation in web services composition

Documents