Semantic Evolution of Geospatial Web Services: Use Cases and Experiments in the Geospatial Semantic Web Joshua Lieberman, Todd Pehle, Mike Dean Traverse Technologies, Inc., Northrop Grumman Information Technology / TASC, BBN Technologies
Overview Geospatial information and Opengeospatial Web Services Geospatial Semantic Web, an interoperability experiment Semantic challenges on the Spatial Web
What are OGC and OWS? The Open Geospatial Consortium, Inc. (OGC) is a non-profit, international, voluntary consensus standards organization that is leading the development of standards for geospatial and location based services Opengeospatial Web Services (OWS) - OGC has been developing for some time specifications for a suite of Web services (sensu lato) and associated encodings to expose geospatial content and operations from distributed content repositories to remote clients across diverse platforms: GML - geographic markup language (an information model and XML schema) for encoding features (geometric representations of geography). Web Feature Service - service providing access to collections of features Web Map Service - service providing access to map layers (cartographically rendered features and images) Catalog Service / Web - service supporting (spatial) discovery of geospatial datasets and services Several other associated specifications
1) GSW Background Geospatial Semantic Web: Use of Semantic Web technologies to discover and reason on geospatial information (UCGIS, Egenhofer, Sheth, etc.) GSW broad research activity sponsored by National Geospatial Intelligence Agency (NGA), undertaken by a number of investigators Interoperability experiment: an Open Geospatial Consortium(OGC) - sanctioned member collaboration to test or refine OWS specifications This GSW IE : activity proposed by NGA, NGIT/TASC, and BBN to test and refine OGC(+) specifications within a scenario for geospatial query with formal semantics: Web Feature Service (WFS) and Filter Encoding (FE) Geography Markup Language (GML) ISO 19115 / 19119 / 1910n / FGDC feature metadata (ISO) Other initial participants: SCO, Jaume I, Muenster, Galdos, GMU,
Drilling Down: The Geospatial part Maps and map visualization Features and feature geometries Geographic and other relationships The Web part Distributed data - maintain locally / access globally Shared services, loosely or tightly coupled to geodata Interoperability between technologies, vendors, architectures The Semantic part Interoperability between communities and domains Softer software Automated reasoning and inference
Geospatial Reasoning: 2-D and Beyond Coordinate relationships Scale significance Coordinate reference systems Topological relationships Network Overlay Spatial inference Proximity Continuity Representation Dimensionality Temporality
The Web Changes Everything (Geospatial) Global communities for local geography Distributed information networks Premium on interoperability The GIS dialtone Maintain locally, access globally Currency is the currency (non-gis) barbarians are at the (GIS) gate
Role of interoperability / opening the temple Focuses on sustained operability - today and the next day Permits separation of concerns Supports information portability Allows component interchangeability Contributes to transparency, testability, and trust Layers of interoperability build on one another Stable syntax promotes shared semantics / understanding Standards are necessary but not sufficient for interoperability
2) Interoperability experiment: goals Exercise current semantic technology in a geospatial realm Demonstrate an end-to-end geospatial semantic query Utilize multiple ontologies for Geointel operations Develop OGC service descriptions with formal semantics (e.g. OWL-S description for Web Feature Service) Develop and test Semantic Web Services interface / role for OGC services Enhance interoperability in a distributed, heterogeneous world, or at least identify the problems
Typical Geospatial Query (Intelligence / Logistics Domain) Which airfields within 500 miles of Kandahar support C5A aircraft? Aero Feature or Geo Feature? Buffer or proximity? Statutory or Nautical? Straight-line or driving? Coordinate system? What does this mean? Afghanistan? Centroid or outline? Feature property or non-spatial information?
Sequence of Experimental Tasks Identify and Build Ontologies for Geospatial / GeoIntel Domains Link Ontologies into Knowledgebase Compose Queries and Query Templates Process Queries Through Knowledgebase Generate and Visualize OWS (WFS) Queries Request Remote Service Descriptions Generate and Distribute Sub-queries
Multiple GSW Ontology Components OGC Services Ontology GeoIntel Problem Domain Ontology NGA Feature Ontology Base Geospatial Ontology Other Base Ontologies
Initial ECDM Selections for Experiment Fuel Repair Service Weather ILS Nav Aids VOR NDB MLS Route Airport TACAN Itinerary Apron Taxiway Runway Plane Threshold Lighting Obstruction
Typical GSW Query Stack Element Query / Visualization Client Query Translator Query Processor Graph Store / Inferencer Geospatial Inferencer Remote WFS harvester Remote WFS translator Remote WFS Function Do CSW query, then WFS query Translate GetRecord to semantic query Process semantic query Query knowledgebase Resolve geospatial relations Add WFS descriptions to knowledgebase Translate between GML / XML & OWL Provide GML features through WFS interface Standardized Web Services interfaces can be (or have been) defined between any two of these stack elements
Model Query Plan Query Client Question Query Rules & Artifacts Knowledge Server Reasoning & Inference WFS Get Feature Template Knowledge Base Sub-query Visualization Client Visualizer Map Domain Ontology Ontologies Service Response Knowledge Server Local Ontologies Remote WFS
GEOINT Query Plan Has Concepts/Relationships, e.g. OWL ontology elements Rules, e.g. RuleML (SWRL) Completion Criteria, e.g. SeRQL query elements (precondition) Inference-based knowledge refinement (precondition) Traversal of geospatial relationships (precondition) Access to remote services through semantic service descriptions Query Client Question Template Domain Ontology Query Rules
(Some) Technology Options Sesame Processing Framework ArcGIS / Gaia Semantic Query Plugin Templates HTTP API REP API GRAPH API Query Layer (SeRQL) GeoSAIL Semantic Feature Visualizer Plugin Oracle 10g DbSAIL DamlDB WebSAIL WFS Java Topology Services
OWL-S Service Description Components and Questions Service Profile Type of Service Themes of Content Provider / business terms Content Description Feature Schema Content Domain Feature Individuals? Service Bindings / Messages Service Grounding Bound Parameters Service Quality Smart Service Consumption Service Model Service Composition
3) Semantic service description: the missing bits <<Content>> description Profile (e.g. ISO 19115) Grounding (bound parameters) Model (e.g. GML, ISO 19110) Interface for query of service description Progressive generalization Discovery Binding Domain Dictionary Individual / Instance Description of service selfdescription
Observations The geospatial realm has well-developed information and service models, but mainly implicit semantics Within the geospatial realm are many communities with only partially shared vocabularies. Gradual adaptation of the existing data and infrastructure is essential Geospatial content is (necessarily) scale-dependent, distributed, heterogeneous, and dynamic - a challenge for description / generalization Geospatial services are typically tightly coupled to content Resolution / traversal of geospatial relationships is a computational challenge Semantic Web Services are essential for opening up the geospatial temple cult but must avoid exchange of one cult for another