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OGC GeoSPARQL : Standardizing Spatial Query on the Semantic Web

OGC GeoSPARQL : Standardizing Spatial Query on the Semantic Web. Matthew Perry, Oracle. 4th Annual Spatial Ontology Community of Practice Workshop USGS, 12201 Sunrise Valley Drive , Reston VA December 2, 2011. Agenda. About the OGC GeoSPARQL SWG Overview of GeoSPARQL Use Cases

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OGC GeoSPARQL : Standardizing Spatial Query on the Semantic Web

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  1. OGC GeoSPARQL: Standardizing Spatial Query on the Semantic Web Matthew Perry, Oracle 4th Annual Spatial Ontology Community of Practice Workshop USGS, 12201 Sunrise Valley Drive , Reston VA December 2, 2011

  2. Agenda • About the OGC GeoSPARQL SWG • Overview of GeoSPARQL • Use Cases • GeoSPARQL Vocabulary • Query Functions • Entailment Components • GeoSPARQL FAQ • Future Work

  3. THE FOLLOWING IS INTENDED TO OUTLINE OUR GENERAL PRODUCT DIRECTION. IT IS INTENDED FOR INFORMATION PURPOSES ONLY, AND MAY NOT BE INCORPORATED INTO ANY CONTRACT. IT IS NOT A COMMITMENT TO DELIVER ANY MATERIAL, CODE, OR FUNCTIONALITY, AND SHOULD NOT BE RELIED UPON IN MAKING PURCHASING DECISION. THE DEVELOPMENT, RELEASE, AND TIMING OF ANY FEATURES OR FUNCTIONALITY DESCRIBED FOR ORACLE'S PRODUCTS REMAINS AT THE SOLE DISCRETION OF ORACLE. 3

  4. About the OGC GeoSPARQL SWG

  5. Group Members • Open Geospatial Consortium standards working group • 13 voting members, 36 observers • Editors: Matthew Perry and John Herring • Chairs: John Herring and Dave Kolas • Submitting Organizations • Australian Bureau of Meteorology • Bentley Systems, Inc. • CSIRO • Defence Geospatial Information Working Group (DGIWG) • GeoConnections - Natural Resources Canada • Interactive Instruments GmbH • Oracle America • Ordnance Survey • Raytheon Company • Traverse Technologies, Inc. • US Geological Survey (USGS)

  6. Standardization Process

  7. GeoSPARQL Overview

  8. Some Use Cases • Existing LOD RDF datasets with some simple spatial data • DBPedia, GeoNames, etc. • Mainly simple, WGS84 Lat Long points • GIS applications with semantically complex thematic aspects • Reasoning based on complex land cover type hierarchy • Qualitative reasoning applications without explicit geometries • RCC8-based reasoning • Data integration applications • RDB2RDF + Federated SPARQL over spatial datasets

  9. Goals for GeoSPARQL • Provide a common target for implementers & users • Oracle, BBN Parliament, Virtuoso, OWLIM, Franz, … • Work within SPARQL’s extensibility framework • Simple enough for general users but capable enough for GIS professionals • Accommodate systems based on qualitative spatial reasoning and systems based on quantitative geometries • Don’t re-invent the wheel! Simple Features Well Known Text (WKT) GML KML GeoJSON ISO 19107 – Spatial Schema ISO 13249 – SQL/MM

  10. A Simple Example Example Data: December 2011 SOCoPWorkshop is located in Reston, VA :OGCSept2011TC :locatedIn :Reston . :Reston :hasPointGeometry [ ogc:asWKT “POINT(-77.2 38.57)”^^ogc:WKTLiteral ] . Example Query: Find airports within 100 KM of Reston, VA SELECT ?airport WHERE { ?airport rdf:type :Airport . ?airport :hasPointGeometry [ ogc:asWKT ?aPointGeom ] FILTER(ogcf:distance(?aPointGeom, “POINT(-77.2 38.57)”^^ogc:WKTLiteral, ogc:km) <= 100) }

  11. What Does GeoSPARQL Give Us? • Vocabulary for Query Patterns • Classes • Spatial Object, Feature, Geometry • Properties • Topological relations • Links between features and geometries • Datatypes for geometry literals • ogc:WKTLiteral, ogc:GMLLiteral • Query Functions • Topological relations, distance, buffer, intersection, … • Entailment Components • RIF rules to expand feature-feature query into geometry query • Gives a common interface for qualitative and quantitative systems

  12. Some Features of the Spec • Uses a Modular Design • Consists of several components • It’s Parameterized • Serialization: WKT, GML, KML, … • Relation Family: Simple Features, Egenhofer, RCC8, … • Benefits • Vendors can easily identify what they support • We support components X, Y and Z for WKT and GML serializations and Simple Features relations • Extensible • Can easily add new components • Can easily add new spatial relations and serializations

  13. GeoSPARQL Vocabulary

  14. GeoSPARQL Vocabulary: Basic Classes and Relations ogc:SpatialObject Same as ISO GM_Object ogc:hasGeometry 0 .. * ogc:Feature ogc:Geometry ogc:dimension : xsd:int ogc:coordinateDimension : xsd:int ogc:spatialDimension : xsd:int ogc:isEmpty : xsd:boolean ogc:isSimple : xsd:boolean ogc:asWKT : ogc:WKTLiteral ogc:asGML : ogc:GMLLiteral … 0 .. 1 metadata ogc:hasDefaultGeometry Same as ISO GFI_Feature serializations Geometry encoded as a Literal

  15. Details of ogc:WKTLiteral All RDFS Literals of type ogc:WKTLiteral shall consist of an optional IRI identifying the spatial reference system followed by Simple Features Well Known Text (WKT) describing a geometric value [ISO 19125-1]. “<http://www.opengis.net/def/crs/OGC/1.3/CRS84> POINT(-122.4192 37.7793)”^^ogc:WKTLiteral WGS84 longitude – latitudeis the default CRS “POINT(-122.4192 37.7793)”^^ogc:WKTLiteral European Petroleum Survey Group (EPSG)maintains a set of CRS identifiers.

  16. Details of ogc:GMLLiteral All ogc:GMLLiterals shall consist of a valid element from the GML schema that implements a subtype of GM_Object as defined in [OGC 07-036]. "<gml:Point srsName=\"http://www.opengis.net/def/crs/OGC/1.3/CRS84\" xmlns:gml=\"http://www.opengis.net/gml\"> <gml:pos>-83.38 33.95</gml:pos> </gml:Point>"^^ogc:GMLLiteral Note that GMLLiterals are NOT rdf:XMLLiterals

  17. Topological Relations between ogc:SpatialObject A A/B A B A B B ogc:sfEquals ogc:sfTouches ogc:sfOverlaps ogc:sfContains A B A B A B B A ogc:sfWithin ogc:sfDisjoint ogc:sfIntersects ogc:sfCrosses Assumes Simple FeaturesRelation Family

  18. RCC8, Egenhofer & Simple Features

  19. Example Data Meta Information :City rdfs:subClassOf ogc:Feature . :Park rdfs:subClassOf ogc:Feature . :exactGeometry rdfs:subPropertyOf ogc:hasGeometry . :Nashua rdf:type :City . :MinesFallsPark rdf:type :Park . :MinesFallsPark :opened “1950-03-01”^^xsd:date . :MinesFallsPark :exactGeometry :geo1 . :geo1 ogc:asWKT “Polygon((…))”^^ogc:WKTLiteral . :Nashua :exactGeometry :geo2 . :geo2 ogc:asWKT “Polygon((…))”^^ogc:WKTLiteral . :MinesFallsPark ogc:sfWithin :Nashua . Non-spatial Properties Spatial Properties

  20. GeoSPARQL Query Functions

  21. GeoSPARQL Query Functions • ogcf:distance(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral, units: xsd:anyURI): xsd:double • ogcf:buffer(geom: ogc:WKTLiteral, radius: xsd:double, • units: xsd:anyURI): ogc:WKTLiteral • ogcf:convexHull(geom: ogc:WKTLiteral): ogc:WKTLiteral geom1 geom2 geom geom

  22. GeoSPARQL Query Functions • ogcf:intersection(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): ogc:WKTLiteral • ogcf:union(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): ogc:WKTLiteral geom2 geom1 geom2 geom1

  23. GeoSPARQL Query Functions • ogcf:difference(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): ogc:WKTLiteral • ogcf:symDifference(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): ogc:WKTLiteral geom2 geom1 geom2 geom1

  24. GeoSPARQL Query Functions • ogcf:envelope(geom: ogc:WKTLiteral): ogc:WKTLiteral • ogcf:boundary(geom1: ogc:WKTLiteral): ogc:WKTLiteral • ogcf:getSRID(geom: ogc:WKTLiteral): xsd:anyURI geom geom

  25. GeoSPARQL Topological Query Functions • ogcf:relate(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral,patternMatrix: xsd:string): xsd:boolean geom1 geom2 ogc:contains patternMatrix: TTTFFTFFT

  26. GeoSPARQL Topological Query Functions • ogcf:sfEquals(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): xsd:boolean • ogcf:sfDisjoint(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): xsd:boolean • ogcf:sfIntersects(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): xsd:boolean • ogcf:sfTouches(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): xsd:boolean • ogcf:sfCrosses(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): xsd:boolean • ogcf:sfWithin(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): xsd:boolean • ogcf:sfContains(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): xsd:boolean • ogcf:sfOverlaps(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): xsd:boolean Assumes Simple FeaturesRelation Family

  27. Example Query Find all land parcels that are within the intersection of :City1 and :District1 PREFIX : <http://my.com/appSchema#> PREFIX ogc: <http://www.opengis.net/geosparql#> PREFIX ogcf: <http://www.opengis.net/geosparql/functions#> PREFIX epsg: <http://www.opengis.net/def/crs/EPSG/0/> SELECT ?parcel WHERE { ?parcel rdf:type :Residential . ?parcel :exactGeometry ?pGeo . ?pGeoogc:asWKT ?pWKT . :District1 :exactGeometry ?dGeo . ?dGeoogc:asWKT ?dWKT . :City1 :extent ?cGeo . ?cGeoogc:asWKT ?cWKT . FILTER(ogcf:sfWithin(?pWKT, ogcf:intersection(?dWKT,?cWKT)))}

  28. Example Query Find the three closest Mexican restaurants PREFIX : <http://my.com/appSchema#> PREFIX ogc: <http://www.opengis.net/geosparql#> PREFIX ogcf: <http://www.opengis.net/geosparql/functions#> PREFIX epsg: <http://www.opengis.net/def/crs/EPSG/0/> SELECT ?restaurant WHERE { ?restaurant rdf:type :Restaurant . ?restaurant :cuisine :Mexican . ?restaurant :pointGeometry ?rGeo . ?rGeoogc:asWKT ?rWKT } ORDER BY ASC(ogcf:distance(“POINT(…)”^^ogc:WKTLiteral, ?rWKT, ogc:KM)) LIMIT 3

  29. GeoSPARQL Entailment Components

  30. GeoSPARQL RDFS Entailment Extension Main Requirements: Basic graph pattern matching shall use the semantics defined by the RDFS Entailment Regime [W3C SPARQL Entailment] Implementations shall support graph patterns involving terms from an RDFS/OWL class hierarchy of geometry types consistent with the one in the specified version of Simple Features / GML

  31. Simple Features Geometry Types ogc:MultiPoint ogc:Point ogc:Geometry ogc:Curve ogc:Surface ogc:GeometryCollection ogc:LineString ogc:Polygon ogc:PolyhedralSurface ogc:Line ogc:LinearRing ogc:Triangle ogc:TIN ogc:MultiSurface ogc:MultiCurve ogc:MultiPolygon ogc:MultiLineString

  32. GeoSPARQL Query Rewrite Extension Find all water bodies within New Hampshire SELECT ?water WHERE { ?water rdf:type :WaterBody . ?water ogc:rcc8Within :NH } Qualitative RCC8 Backward Chaining Same Query Specification Quantitative SELECT ?water WHERE { ?water rdf:type :WaterBody . ?water ogc:hasDefaultGeometry ?wGeo . ?wGeoogc:asWKT ?wWKT . :NH ogc:hasDefaultGeometry ?nGeo . ?nGeoogc:asWKT ?nWKT . FILTER(ogcf:rcc8Within(?wWKT, ?nWKT)) } Query Rewrite Specified with a RIF rule

  33. GeoSPARQL Query Rewrite Extension Main Requirement: Basic graph pattern matching shall use the semantics defined by the RIF Core Entailment Regime [W3C SPARQL Entailment] for the RIF rules [W3C RIF Core] geor:sf-equals, geor:sf-disjoint, geor:sf-intersects, geor:sf-touches, geor:sf-crosses, geor:sf-within, geor:sf-contains, geor:sf-overlaps.

  34. Query Rewrite Rules • Used to compute Feature-Feature spatial relations based on default geometries • Specified as a collection of RIF rules • Example: ogcr:sfEquals (Forall ?f1 ?f2 ?g1 ?g2 ?g1Serial ?g2Serial (f1[ogc:sfEquals->?f2] :- And (?f1[ogc:hasDefaultGeometry->?g1] ?f2[ogc:hasDefaultGeometry->?g2] ?g1[ogc:asWKT->?g1Serial] ?g2[ogc:asWKT->?g2Serial] External(ogcf:sfEquals(?g1Serial,?g2Serial))) ) )

  35. Summary of Conformance Classes Parameters Core • Serialization • WKT • GML • Relation Family • Simple Features • RCC8 • Egenhofer Topology Vocabulary Extension (relation_family) Geometry Extension (serialization, version) Determines geometry classes and geometry literal datatype Geometry Topology Extension (serialization, version, relation_family) Query Rewrite Extension (serialization, version, relation_family) RDFS Entailment Extension (serialization, version, relation_family) Determines topology properties and topology functions

  36. GeoSPARQL FAQ

  37. Why don’t you have ogc:myFavoriteProperty? • GeoSPARQL vocabulary is not comprehensive • Just enough to define a reasonable set of query patterns • There are other efforts for more comprehensive vocabularies • ISO / TC 211 • SOCoP • GeoVocamps • GeoSPARQL vocabulary can easily be extended with other application/domain-specific vocabularies

  38. Why Encode Geometry Data as a Literal? Advantage: single self-contained unit Consistent way to select geometry information Find all water bodies that are within 1 km of Route 3 SELECT ?water ?wWKT WHERE { ?water rdf:type :WaterBody . ?water :hasExactGeometry ?wGeo . ?wGeoogc:asWKT ?wWKT . :Route_3 :hasExactGeometry ?r3Geo . :r3Geo ogc:asWKT ?r3WKT . FILTER(ogcf:distance(?r3WKT, ?wWKT,…) <= 1000) } Consistent way to pass geometry information around

  39. Why is SRID encoded in Geometry Literal? • The query functions need the SRID to perform computations • SRID is really a property of the serialization not fundamental to the geometry itself • GML already encodes it, only WKT has to be modified • Adding a separate property is redundant and potentially inconsistent • Note: geometry type class is also redundant but can be useful for entailment • We have an ogcf:getSRID() function to aid in filtering based on SRID

  40. Why don’t you support W3C Basic Geo? • Too simple to meet our requirements • Can’t use different datums and coordinate systems • Limited number of geometry types • W3C Basic Geo data can easily be converted to WKTLiteral PREFIX geo: <http://www.w3.org/2003/01/geo/wgs84_pos#> PREFIX ogc: <http://www.opengis.net/def/dataType/OGC-SF/1.0/> SELECT (STRDT(CONCAT("POINT(",?long," ",?lat,")"), ogc:WKTLiteral) AS ?wktLit) WHERE { ?point geo:long ?long . ?point geo:lat ?lat }

  41. Can I support both GML and WKT? • YES • A valid GMLLiteral is an invalid WKTLiteral and vice versa • An operation on these two objects is an error according to the GeoSPARQL spec, but … From Section 11.3.1 of the SPARQL specification [W3C SPARQL] (http://www.w3.org/TR/rdf-sparql-query/#operatorExtensibility): SPARQL language extensions may provide additional associations between operators and operator functions; this amounts to adding rows to the table above. No additional operator may yield a result that replaces any result other than a type error in the semantics defined above. The consequence of this rule is that SPARQL extensions will produce at least the same solutions as an unextended implementation, and may, for some queries, produce more solutions.

  42. Why no Universal Geometry Ontology? • Geometry types in existing standards are different abstractions • e.g. Polygon edges can be arcs in ISO 19107 / GML but must be straight lines in Simple Features • Any hierarchy we get may be too restrictive • You should be able to conceptualize a geometry any way you want as long as you can support the required operations. • All we’re left with is a single root Geometry class in the core vocabulary • More detailed Geometry types are available with RDFS Entailment Extension • Supported Geometry types tied to serialization • Can’t use a geometry type if you can’t serialize it

  43. Why do I have to support RDFS entailment? • Support for only geometry literals and query functions could be a popular use case • All entailment requirements are contained in a separate conformance class • RDFS Entailment Extension (serialization, version) • Query Rewrite Extension (serialization, version, relation_family)

  44. Summary • GeoSPARQL Defines: • Basic vocabulary, Query functions, Entailment component • Based on existing OGC/ISO standards • WKT, GML, Simple Features, ISO 19107 • Uses SPARQL’s built-in extensibility framework • Modular specification • Allows flexibility in implementations • Easy to extend • Accommodates qualitative and quantitative systems • Same query specification for qualitative (core + topology vocabulary) and quantitative (all components, incl. query rewrite)

  45. Future Work • Define new conformance classes • KML, GeoJSON • Define OWL axioms for qualitative spatial reasoning • ogc:sfWithin rdf:type owl:TransitiveProperty • Hybrid qualitative / quantitative spatial reasoning • Define standard methodology for (virtually) converting legacy feature data represented using the general feature model to RDF (RDB2RDF for spatial)

  46. Questions? Thanks to all members of the GeoSPARQL SWG !

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