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OGC GeoSPARQL: Standardizing Spatial OGC GeoSPARQL: Standardizing Spatial Query on the Semantic WebQuery 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

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AgendaAgenda

• About the OGC GeoSPARQL SWG

• Overview of GeoSPARQL– Use Cases– GeoSPARQL Vocabulary– Query Functions– Entailment Components

• GeoSPARQL FAQ

• Future Work

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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.

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About the OGC GeoSPARQL SWGAbout the OGC GeoSPARQL SWG

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Group MembersGroup 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)

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Standardization ProcessStandardization Process

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GeoSPARQL OverviewGeoSPARQL Overview

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Some Use CasesSome 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

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Goals for GeoSPARQLGoals 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!

ISO 19107 – Spatial SchemaISO 13249 – SQL/MM

Simple FeaturesWell Known Text (WKT)GMLKMLGeoJSON

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A Simple ExampleA Simple Example

:OGCSept2011TC :locatedIn :Reston .:Reston :hasPointGeometry [

ogc:asWKT “POINT(-77.2 38.57)”^^ogc:WKTLiteral ] .

Example Data: December 2011 SOCoP Workshop is located in Reston, VA

SELECT ?airportWHERE { ?airport rdf:type :Airport . ?airport :hasPointGeometry [ ogc:asWKT ?aPointGeom ] FILTER(ogcf:distance(?aPointGeom, “POINT(-77.2 38.57)”^^ogc:WKTLiteral, ogc:km) <= 100) }

Example Query: Find airports within 100 KM of Reston, VA

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What Does GeoSPARQL Give Us?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

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Some Features of the SpecSome 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

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GeoSPARQL VocabularyGeoSPARQL Vocabulary

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serializations

metadata

ogc:SpatialObject

ogc:Feature0 .. *

0 .. 1

ogc:hasGeometry

ogc:hasDefaultGeometry

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

…

GeoSPARQL Vocabulary: Basic Classes and RelationsGeoSPARQL Vocabulary: Basic Classes and Relations

Same as ISO GFI_Feature

Same as ISO GM_Object

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Geometry encoded as a Literal

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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

European Petroleum Survey Group (EPSG)maintains a set of CRS identifiers.

WGS84 longitude – latitudeis the default CRS

“POINT(-122.4192 37.7793)”^^ogc:WKTLiteral

Details of ogc:WKTLiteralDetails of ogc:WKTLiteral

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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].

Details of ogc:GMLLiteralDetails of ogc:GMLLiteral

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"<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

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A/B A B A B A B

A B A B BBA

ogc:sfEquals ogc:sfTouches ogc:sfOverlaps ogc:sfContains

ogc:sfWithin ogc:sfDisjoint ogc:sfIntersects ogc:sfCrosses

Topological Relations between ogc:SpatialObjectTopological Relations between ogc:SpatialObject

Assumes Simple FeaturesRelation Family

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A

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RCC8, Egenhofer & Simple FeaturesRCC8, Egenhofer & Simple Features

Simple Features Egenhofer RCC8

equals equal EQ

disjoint disjoint DC

intersects ¬ disjoint ¬ DC

touches meet EC

within inside+coveredBy NTPP+TPP

contains contains+covers NTPPi+TPPi

overlaps overlap PO

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: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 .

Meta Information

Non-spatial Properties

Spatial Properties

Example DataExample Data

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GeoSPARQL Query FunctionsGeoSPARQL Query Functions

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– 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

GeoSPARQL Query FunctionsGeoSPARQL Query Functions

geom

geom1 geom2

geom

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GeoSPARQL Query FunctionsGeoSPARQL Query Functions

– ogcf:intersection(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): ogc:WKTLiteral

– ogcf:union(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): ogc:WKTLiteral

geom1

geom2

geom1

geom2

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GeoSPARQL Query FunctionsGeoSPARQL Query Functions

– ogcf:difference(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): ogc:WKTLiteral

– ogcf:symDifference(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral): ogc:WKTLiteral

geom1

geom2

geom1

geom2

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– ogcf:envelope(geom: ogc:WKTLiteral): ogc:WKTLiteral

– ogcf:boundary(geom1: ogc:WKTLiteral): ogc:WKTLiteral

– ogcf:getSRID(geom: ogc:WKTLiteral): xsd:anyURI

GeoSPARQL Query FunctionsGeoSPARQL Query Functions

geom

geom

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– ogcf:relate(geom1: ogc:WKTLiteral, geom2: ogc:WKTLiteral, patternMatrix: xsd:string): xsd:boolean

GeoSPARQL Topological Query FunctionsGeoSPARQL Topological Query Functions

DE-9IM Intersection Matrix

geom2

Interior Boundary Exterior

geom1Interior T T T

Boundary F F T

Exterior F F T

geom1

geom2

ogc:contains

patternMatrix: TTTFFTFFT

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– 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

GeoSPARQL Topological Query FunctionsGeoSPARQL Topological Query Functions

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Assumes Simple FeaturesRelation Family

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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 ?parcelWHERE { ?parcel rdf:type :Residential . ?parcel :exactGeometry ?pGeo . ?pGeo ogc:asWKT ?pWKT .

:District1 :exactGeometry ?dGeo . ?dGeo ogc:asWKT ?dWKT .

:City1 :extent ?cGeo . ?cGeo ogc:asWKT ?cWKT . FILTER(ogcf:sfWithin(?pWKT, ogcf:intersection(?dWKT,?cWKT)))}

Find all land parcels that are within the intersection of :City1 and :District1

Example QueryExample Query

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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 ?restaurantWHERE { ?restaurant rdf:type :Restaurant . ?restaurant :cuisine :Mexican . ?restaurant :pointGeometry ?rGeo . ?rGeo ogc:asWKT ?rWKT }ORDER BY ASC(ogcf:distance(“POINT(…)”^^ogc:WKTLiteral, ?rWKT, ogc:KM))LIMIT 3

Find the three closest Mexican restaurants

Example QueryExample Query

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GeoSPARQL Entailment ComponentsGeoSPARQL Entailment Components

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GeoSPARQL RDFS Entailment ExtensionGeoSPARQL RDFS Entailment Extension

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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

Main Requirements:

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Simple Features Geometry TypesSimple Features Geometry Types

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:MultiPoint

ogc:MultiPolygon ogc:MultiLineString

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SELECT ?waterWHERE { ?water rdf:type :WaterBody . ?water ogc:rcc8Within :NH }

Find all water bodies within New Hampshire

RCC8 Backward Chaining

SELECT ?waterWHERE { ?water rdf:type :WaterBody . ?water ogc:hasDefaultGeometry ?wGeo . ?wGeo ogc:asWKT ?wWKT . :NH ogc:hasDefaultGeometry ?nGeo . ?nGeo ogc:asWKT ?nWKT . FILTER(ogcf:rcc8Within(?wWKT, ?nWKT)) }

Same Query SpecificationQualitative

Quantitative

Query Rewrite

Specified with a RIF rule

GeoSPARQL Query Rewrite ExtensionGeoSPARQL Query Rewrite Extension

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GeoSPARQL Query Rewrite ExtensionGeoSPARQL Query Rewrite Extension

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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.

Main Requirement:

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Query Rewrite RulesQuery 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))) ))

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Summary of Conformance ClassesSummary of Conformance Classes

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Core

Topology Vocabulary Extension (relation_family)

Geometry Extension (serialization, version)

Geometry Topology Extension (serialization, version, relation_family)

Query Rewrite Extension (serialization, version, relation_family)

RDFS Entailment Extension (serialization, version, relation_family)

Parameters

• Serialization– WKT– GML

• Relation Family– Simple Features– RCC8– Egenhofer

Determines geometry classes and geometry literal datatype

Determines topologyproperties and topology functions

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GeoSPARQL FAQGeoSPARQL FAQ

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Why don’t you have ogc:myFavoriteProperty?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

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Advantage: single self-contained unit

SELECT ?water ?wWKTWHERE { ?water rdf:type :WaterBody . ?water :hasExactGeometry ?wGeo . ?wGeo ogc:asWKT ?wWKT . :Route_3 :hasExactGeometry ?r3Geo . :r3Geo ogc:asWKT ?r3WKT . FILTER(ogcf:distance(?r3WKT, ?wWKT,…) <= 1000) }

Find all water bodies that are within 1 km of Route 3

Consistent way to pass geometry information around

Consistent way to select geometry information

Why Encode Geometry Data as a Literal?Why Encode Geometry Data as a Literal?

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Why is SRID encoded in Geometry Literal?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

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Why don’t you support W3C Basic Geo?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 }

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Can I support both GML and WKT?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 …

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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.

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Why no Universal Geometry Ontology?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

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Why do I have to support RDFS entailment?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)

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SummarySummary

• 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)

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Future WorkFuture 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)

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Questions?Questions?

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Thanks to all members of the GeoSPARQL SWG !