A Logical Framework for Web Service Discovery The Third International Semantic Web Conference Hiroshima, Japan, Michael Kifer 1, Rubén Lara 2, Axel Polleres 2, Chang Zhao 1, Uwe Keller 2, Holger Lausen 2, and Dieter Fensel 2 Department of Computer Science University at Stony Brook, New York, USA 1 Department of Computer Science University at Stony Brook, New York, USA Digital Enterprise Research Institute, Innsbruck, Austria, and Galway, Ireland 2 Digital Enterprise Research Institute, Innsbruck, Austria, and Galway, Ireland

Rubén Lara 2 Overview 1.Introduction 2.Proof obligations and formalization 3.Realization 4.Semantics of rule reification 5.Conclusions & future work

Rubén Lara 3 Automatic discovery Current Web Services have to be selected and hard-wired at design time –No dynamic reconfiguration of services Semantics can enable the automatic location of Web Services providing particular functionality

Rubén Lara 4 WSMO & WSML Objectives that a client may have when consulting a Web Service Provide the formally specified terminology used by all other components Semantic description of Web Services: - Capability - Interfaces Connectors between components to bypass heterogeneity F-Logic + Transaction Logic

Rubén Lara 5 The problem Matching capabilities of existing Web Services against the goal described by the requester –Consideration of the functionality of the Web Service –Distinction between discovery and contracting –Example implementation using

Rubén Lara 6 Overview 1.Introduction 2.Proof obligations and formalization 3.Realization 4.Semantics of rule reification 5.Conclusions & future work

Rubén Lara 7 Goals, capabilities & mediators Goal describes (in terms of domain ontologies) the desired state of: –Information space –State of the world Web Service capabilities describe (in terms of domain ontologies): –What the service expects to provide its functionality –What is guaranteed to hold after execution wgMediators link Web Services and goals, resolving heterogeneity –Resolve possible terminology differences

Rubén Lara 8 Logics and scalability issues Logic can be used to formalize goals, capabilities and proof obligations –Scalable framework must rely on a relatively small number of logicians Customer: - no training in KR -pre-defined discovery queries -goal ontology Service Provider: - modest requirements -Capabilities written to relatively simple ontologies -Relatively simple types of rules Mediation Provider: - Bulk of logical expertise -Link ontologies, not customers and providers

Rubén Lara 9 Proof obligations (I) Set of imported ontologies O Goal G Service capability C (C eff and C pre ) wgMediator wg –takes a goal G and constructs input In wg (G) suitable for services mediated –Converts the goal into a postcondition Post wg (G) expressed in terms of the service ontology –Mediation can be complex: Goals can be expressed in a very high level syntax Service capabilities can be rather simple

Rubén Lara 10 Proof obligations (II) Service discovery –Given a goal G, can the service execute in a way such that G can be achieved? Service contracting –Given an actual input to a specific service, does this input lead to the results expected by the requester?

Rubén Lara 11 Proof obligations (III) Proof obligations before –Deal with a particular service –Different services have different effects Use of transaction logic is the sequence operator is the hypothetical operator

Rubén Lara 12 Overview 1.Introduction 2.Proof obligations and formalization 3.Realization 4.Semantics of rule reification 5.Conclusions & future work

Rubén Lara 13 Realization Use of : –Support for F-Logic, HiLog, Transaction Logic and rule reification Geographic ontology

Rubén Lara 14 Realization (II) Goal ontology: Service1: Conditions over the input Input is a search -> provide itinerary wgMediator used

Rubén Lara 15 Realization (III) Service 3: Goals: Uses goal ontology Region!

Rubén Lara 16 Realization (IV) Mediator: Takes the goal and constructs input to the service Takes the result and checks it according to the format specified in the goal

Rubén Lara 17 Realization Discovery Construct input Generate effects Assume effects Check goal Remove effects

Rubén Lara 18 Overview 1.Introduction 2.Proof obligations and formalization 3.Realization 4.Semantics of rule reification 5.Conclusions & future work

Rubén Lara 19 Semantics of rule reification Model theory for F-Logic extended with rule reification defined Reified F-Logic avoids paradoxes through two restrictions: –No negation is allowed in the rule head, and –Reification of negation of any fact or any rule is not permitted

Rubén Lara 20 Overview 1.Introduction 2.Proof obligations and formalization 3.Realization 4.Semantics of rule reification 5.Conclusions & future work

Rubén Lara 21 Conclusions Logical framework and realization for: –dynamic discovery of Web Services –verification of contractual statements Scalable framework in terms of human resources by exploiting mediators The framework captures the relation between inputs and effects, thus providing more accurate descriptions and discovery Easily extendable to include invocation

Rubén Lara 22 Future work In progress –Alignment with WSML –Integration with other types of web service discovery –Further investigation on border between ggMediation and wgMediation –Complete knowledge goals in the absence of sufficient domain knowledge –Implementation of WSMO discovery engine Planned –Integration with composition

Rubén Lara 23 Conclusions