Describing OGC WMS and WFS with the OWL-S Web Service Ontology Dr Kristin Stock Allworlds Geothinking, UK Centre for Geospatial Science, University of Nottingham, UK EDINA, UK

Introduction COMPASS Project ( COMPASS Project ( OGC Standards focus on syntactic descriptions of web services. OGC Standards focus on syntactic descriptions of web services. Some recent work incorporates object semantics. Some recent work incorporates object semantics. Nothing so far done on semantics of functionality. Nothing so far done on semantics of functionality. We tried to fill this gap with OWL-S. We tried to fill this gap with OWL-S.

Why do this? Web service ontologies are intended to assist with: Web service ontologies are intended to assist with: –Discovery –Dynamic execution –Chaining Automating the publish-find-bind model. Automating the publish-find-bind model.

OWL-S One of the dominant web service ontologies (cf WSMO). One of the dominant web service ontologies (cf WSMO). The basic model: The basic model: –Profile – advertises what the service does; –Process Model – describes the process that it executes; –Grounding – describes how it can be executed. Inputs, Outputs, Preconditions, Results Inputs, Outputs, Preconditions, Results

Service ServiceGrounding ServiceProfile ServiceModel presents (what it does) supports (how to access it) describedBy (how it works) Domain Ontology (Feature Types) Inputs, Outputs, Preconditions and Results Inputs, Outputs, Preconditions and Results

GetCapabilities Content of GetCapabilities mapped to OWL-S. Content of GetCapabilities mapped to OWL-S. This process could be automated for WFS and WMS. This process could be automated for WFS and WMS. Augment with semantic links. Augment with semantic links.

The OWL-S OGC Ontology (1) Created an OWL-S OGC Ontology to describe the specifications. Created an OWL-S OGC Ontology to describe the specifications. Each implementation of a WFS or WMS imports the OWL-S OGC Ontology and creates instances. Each implementation of a WFS or WMS imports the OWL-S OGC Ontology and creates instances.

The OWL-S OGC Ontology (2) For WFS and WMS, the OWL-S OGC Ontology is quite comprehensive, because specs are specific – wouldn’t be so for WPS. For WFS and WMS, the OWL-S OGC Ontology is quite comprehensive, because specs are specific – wouldn’t be so for WPS.

OWL-S OGC Ontology: What’s in it? Classes for: Classes for: –WFS and WMS specialised service; –The processes that a WMS or WFS may offer and inputs and outputs; –An OGCHttp Grounding and operations; –Connections between processes and the operations that implement them.

The Grounding OWL-S has a WSDL grounding. OWL-S has a WSDL grounding. We didn’t use it because it’s XML, not OWL – doesn’t fit our architecture. We didn’t use it because it’s XML, not OWL – doesn’t fit our architecture. Could have applied the WSDL – RDF mapping but time limited. Could have applied the WSDL – RDF mapping but time limited. Created a new grounding. Created a new grounding.

OGCHttpGroundin g OGCHttpOperation OGCHttpParameter DomainQueryModel OGCHttpConstraint hasOGCHttpOperation hasOGCHttpParameter hasOGCHttpConstraint hasDomain hasQueryModelhasDomain CheckBox InputBoxOptionList RadioButto n isA Process:Parameter groundsAbstractParameter Children of Process:AtomicProcess (for each WFS and WMS operation) groundsAtomicProcess has Input has Output Meaning PossibleValue s DefaultValue DataType DomainMetadat a ValuesUnit hasComponent

How exactly does this describe the semantics? IOPR describe semantics of functionality; IOPR describe semantics of functionality; Process describes steps/branches/loops etc. (not implemented) Process describes steps/branches/loops etc. (not implemented) IOPR can be connected to concepts in a domain ontology; IOPR can be connected to concepts in a domain ontology; OWL-S OGC ontology includes hasTopic to link service, feature type or layer. OWL-S OGC ontology includes hasTopic to link service, feature type or layer.

Dynamic service execution Grounding includes binding between operation parameters and ‘query model’. Grounding includes binding between operation parameters and ‘query model’. This is information that can be used to dynamically generate form to ask user for input. This is information that can be used to dynamically generate form to ask user for input. e.g. Which feature type they would like to query in WFS, layer in WMS. e.g. Which feature type they would like to query in WFS, layer in WMS.

What’s in the ontology for each web service? Details from GetCapabilities, including: Details from GetCapabilities, including: –Which operations are implemented; –Actual grounding (URLs) and query model; –etc. Semantic hasTopic links; Semantic hasTopic links; You don’t have to repeat IOPR. You don’t have to repeat IOPR.

What did we find? It’s very cumbersome. It’s very cumbersome. Full implementation of OWL-S includes IOPR more than once (different purposes); Full implementation of OWL-S includes IOPR more than once (different purposes); Difficulties with cardinality constraints. Difficulties with cardinality constraints.

How did we modify OWL-S? Did not describe IOPR multiple times, but once with references, same for parameters. Did not describe IOPR multiple times, but once with references, same for parameters. New grounding. New grounding. Did not define IOPR in each instance ontology, just referenced. Did not define IOPR in each instance ontology, just referenced.

It’s a limited implementation Didn’t fully describe preconditions and results. Didn’t fully describe preconditions and results. Didn’t fully model the complexity of some parameters. Didn’t fully model the complexity of some parameters. Process model limited. Process model limited.

Conclusions Full OWL-S implementation impractical. Full OWL-S implementation impractical. OGC specifications make it easier to use OWL-S. OGC specifications make it easier to use OWL-S. OWL-S can be used to support discovery and execution. OWL-S can be used to support discovery and execution. Didn’t test orchestration. Didn’t test orchestration.

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