Representing and Querying Linked Geospatial Data Kostis Kyzirakos - PowerPoint PPT Presentation

Representing and Querying Linked Geospatial Data Kostis Kyzirakos kostis@cwi.nl Centrum voor Wiskunde en Informatica Database Architectures group Amsterdam Geonovum The Netherlands April 11, 2014

Outline  The data model stRDF and the query language stSPARQL  The system Strabon  Visualizing time-evolving geometries using Sextant  Real-Time Fire Monitoring application  Conclusions

 The data model The data m odel stRDF and the query language stSPARQL  The system Strabon stRDF and the  Visualizing time- evolving geometries using query language Sextant  Real-Time Fire Monitoring stSPARQL application  Conclusions

Linked Open Data Cloud

5 RDF: Resource Description Framew ork W 3 C recommendation RDF is a graph data m odel  Resources are described in terms of properties and property values using RDF statem ents  Statements are represented as triples , consisting of a subject , predicate and object . dbpedia: " 614,543"^^xsd:integer Rotterdam ex:hasPopulation 5

The Data Model stRDF  stRDF stands for spatial/ tem poral RDF.  It is an extension of the W3C standard RDF for the representation of geospatial data that m ay change over tim e .  stRDF extends RDF with:  Spatial literals encoded in OGC standards Well-Known Text or GML  New datatypes for spatial literals ( strdf:WKT , strdf:GML and strdf:geometry )  Tem poral literals can be either periods or instants  New datatype for temporal literals ( strdf:period )  Placed as the fourth component of a triple to denote valid time

RDF: An example 7

stRDF: An example ( 1/ 2) noa:hasI "1"^^xsd:int noa:BurntArea D rdf:type ex:BurntArea1 "23.7636"^^ noa:hasArea xsd:double Spatial Literal (OpenGIS Simple geo:geometry Features) "POLYGON(( 38.16 23.7, 38.18 23.7, ...38.16 23.8, 38.16 3.7)); <http://spatialreference.org/ref/epsg/4121 />"^^strdf:WKT Spatial Data Type Well-Known Text

9 stRDF: An example dbpedia:City RDF rdf:type ex:Piraeus rdf:type OGC standards ex:hasLocation ex:Haven sRDF ex:PiraeusLoc ex:hasSpatialExtent Spatial Literal (OpenGIS Simple "POLYGON((38.16 23.7, 38.18 23.7, Features) ... 38.16 23.8, 38.16 3.7)); <http://spatialreference.org/ref/epsg/4121/> "^^strdf:WKT Spatial Data Type Well-Known Text

The stRDF Data Model strdf:geometry rdf:type rdfs:Datatype; rdfs:subClassOf rdfs:Literal. strdf:WKT rdf:type rdfs:Datatype; rdfs:subClassOf strdf:geometry. strdf:GML rdf:type rdfs:Datatype; rdfs:subClassOf strdf:geometry.

W KT Class Hierarchy 11

stSPARQL: An example ( 1/ 2) • Find all burned forests within 10kms of a city select ?BA ?BAGEO where { ?R rdf:type noa:Region ; geo:geometry ?RGEO ; noa:hasCorineLandCoverUse ?F . ?F rdfs:subClassOf clc:Forests . ?CITY rdf:type dbpedia:City ; Spatial Functions geo:geometry ?CGEO . (OGC Simple ?BA rdf:type noa:BurntArea ; Feature Access) geo:geometry ?BAGEO . filter( strdf:Intersect(?RGEO,?BAGEO) && strdf:Distance(?BAGEO,?CGEO,uom:km)<10)}

stRDF: An example ( 2/ 2) clc:region1 clc:hasLandCover clc:Forest . clc:region1 clc:hasLandCover clc:Forest "[2006-08- 25T11:00:00+02,2007-08- 25T11:00:00+02)"^^ strdf:period . noa:ba1 rdf:type noa:BurntArea "[2007-08-25T11:00:00+02,2009-08- 25T11:00:00+02)"^^ strdf:period . clc:region1 clc:hasLandCover clc:AgriculturalArea "[2009-08-25T11:00:00+02, " UC ")"^^ strdf:period . 13 1 3

stSPARQL: An example ( 2/ 2) • Find all areas that were forests in 2006 and got burned later within 10kms of a city select ?BA ?BAGEO where { ?R rdf:type noa:Region ; geo:geometry ?RGEO ; noa:hasCorineLandCoverUse ?F ?t1. . ?F rdfs:subClassOf clc:Forests . Spatial ?CITY rdf:type dbpedia:City ; Functions geo:geometry ?CGEO . (OGC Simple Temporal ?BA rdf:type noa:BurntArea ?t2; Feature Access) constant and geo:geometry ?BAGEO . extension function filter( strdf:Intersect(?RGEO,?BAGEO) && strdf:Distance(?BAGEO,?CGEO,uom:km)<10) filter( strdf:during(?t1, “[2006-01-01:00:00:01, 2006-01-01:23:59:59]”^^strdf:period)) && strdf:before(?t1, ?t2) }

stSPARQL: Geospatial SPARQL 1.1 We define a SPARQL extension function for each function defined in the OpenGI S Sim ple Features Access standard  Basic functions  Get a property of a geometry (e.g., strdf:srid )  Get the desired representation of a geometry (e.g., strdf:AsText )  Test whether a certain condition holds (e.g., strdf:IsEmpty , strdf:IsSimple )  Functions for testing topological spatial relationships ( e.g., strdf:equals , strdf:intersects )  Spatial analysis functions  Construct new geometric objects from existing geometric objects (e.g., strdf:buffer , strdf:intersection , strdf:convexHull )  Spatial metric functions (e.g., strdf:distance , strdf:area )  Spatial aggregate functions (e.g., strdf:union , strdf:extent )  We add a set of tem poral functions (superset of Allen’s functions) as SPARQL extension functions

1 6 The OGC Standard GeoSPARQL Core Param eters Topology Vocabulary Geometry Extension Serialization - serialization  Extension - version - relation family WKT  GML  Geometry Topology Relation Fam ily  Extension - serialization Simple  - version - relation family Features RCC-8  Query Rewrite RDFS Entailment Egenhofer  Extension Extension - serialization - serialization - version - version - relation family - relation family

 The data model The system stRDF and the query language stSPARQL  The system Strabon Strabon  Visualizing time- evolving geometries using Sextant  Real-Time Fire Monitoring application  Conclusions http://strabon.di.uoa.gr

1 8 Strabon Architecture WKT GML Sesame Time stRDF graphs stSPARQL/ GeoSPARQL queries SPARQL results KML Documents GeoJSON

1 9 Real-w orld W orkload: 500 million triples – cold caches Response time (sec) Response time (sec) number of Nodes in query region number of Nodes in query region Thematic selectivity: 0.1% Thematic selectivity: 100%

2 0 Geographica Synthetic Workload ( Spatial Selections, cold caches) Intersects Intersects Thematic Selectivity: 0.2% Thematic Selectivity: 100% http://geographica.di.uoa.gr

2 1 Results ( points only) Synthetic Workload ( Spatial Selections, cold caches) Intersects Intersects Thematic Selectivity: 0.1% Thematic Selectivity: 100%

2 2 Geographica Synthetic Workload ( Spatial Joins) Intersects http://geographica.di.uoa.gr

System Language Index Geometries CRS support Geospatial Function Support Strabon stSPARQL/ R-tree-over- WKT / GML • OGC-SFA Yes • Egenhofer GeoSPARQL* GiST support • RCC-8 Parliament GeoSPARQL* R-Tree WKT / GML •OGC-SFA Yes •Egenhofer support •RCC-8 •OGC-SFA Oracle GeoSPARQL R-Tree, WKT / GML Yes •Egenhofer Quadtree support •RCC-8 Brodt et al. SPARQL R-Tree WKT support No OGC-SFA (RDF-3X) RCC-8 Perry SPARQL-ST R-Tree GeoRSS GML Yes •Buffer AllegroGraph Extended Distribution 2D point •Bounding Box SPARQL sweeping geometries Partial •Distance technique •Point-in-polygon OWLIM Extended Custom 2D point No •Buffer SPARQL geometries •Distance SQL/MM (subset) Virtuoso SPARQL R-Tree 2D point Yes geometries OGC-SFA uSeekM GeoSPARQL R-tree-over WKT support GiST No

 The data model Visualizing tim e- stRDF and the query language stSPARQL  The system Strabon evolving  Visualizing time- evolving geometries using geom etries using Sextant  Real-Time Fire Monitoring Sextant application  Conclusions http://sextant.di.uoa.gr

Rapid Mapping application http://bit.ly/sextant-rapid-mapping-attica

Evolution of Land Cover http://bit.ly/sextant-land-cover-evolution

 The data model Real-Tim e stRDF and the query language stSPARQL  The system Strabon Fire Monitoring  Visualizing time- evolving geometries using Sextant  Real-Time Fire Monitoring application  Conclusions http://bit.ly/FiresInGreece

W ildfire Monitoring and Burnt Area Mapping ( NOA)

High Level Data Modeling  Need for representing  Standard product m etadata  Standard product sem antic annotations  Geospatial inform ation  Tem poral inform ation  Need to link to other data sources  GI S data  Other information on the W eb

Fire Monitoring Application  Improving the fire monitoring service using Semantic Web technologies  Representing fire related products using ontologies  Enriching products with linked geospatial data  Improving accuracy with respect to:  Underlying land cover/land use  Persistence in time

NOA Ontology

Linked Geospatial Data  Datasets that we developed and published as linked data:  Corine Land Use / Land Cover  Coastline of Greece  Greek Administrative Geography  Portal: http:/ / w w w .linkedopendata.gr/  Datasets from Linked Open Data Cloud  LinkedGeoData  GeoNames

Linked Open Data