Download - Representation, Querying and Visualisation of Linked ...!3 Why Spatial (and Temporal) Data? • Spatial and temporal data are very important in reality: Everything that happens, happens

Representation,QueryingandVisualisationofLinkedGeospatialData

KonstantinaBeretaandGeorgeStamoulis

RoDTutorialOctober4,2018

Outline

• Introduction• Previousrelatedresearchinotherareas• Motivation• ExtensionsofRDFandSPARQLfortherepresentationandqueryingofgeospatialdata

• Geospatialdescriptionlogicsandgeospatialontology-baseddataaccesssystems

• Implementedsystems,evaluationandcomparison• Visualisationoflinkedgeospatialdata• Openissues

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WhySpatial(andTemporal)Data?

• Spatialandtemporaldataareveryimportantinreality:Everythingthathappens,happenssometime,somewhere.

• Decisionmakingcanbesubstantiallyimprovedifweknowwhenandwherethingstakeplace.

• Thistutorialisforthe“where”.

PreviousResearch

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GeographicInformationSystems(GIS)Research• LotsofinterestingtheoreticalandpracticalworkbyGISresearchers.

• Topicscovered:– Geographicdataandtheirrepresentation– Geographicdatamodellingandgeographicdatabases

– GISsoftware– Cartographyandmapproduction– Spatialdataanalysisanddecisionmaking– GeospatialdataontheWeb

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GeographicInformationSystemsResearch(cont’d)• Industrialimpact:– LotsofrelevantstandardsbytheOpenGeospatialConstortium(OGC).

– State-of-the-artGISsoftwaree.g.,ArcGISorQGIS.

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GeographicInformationSystemsResearch(cont’d)• Educationalimpact:– Relevantideashavefoundtheirwayinwell-knownGISbooks.

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SpatialDatabaseResearch

• Lotsofinterestingtheoreticalandpracticalworkbydatabaseresearchers.

• Topicscovered:– Datamodelsandquerylanguages– Storagestructuresandindexingtechniques– Queryprocessing– Userinterfaces– Implementedsystems– Applications

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SpatialDatabaseResearch(cont’d)

• Industrialimpact:– TheOGCstandard“OpenGISSimpleFeatureAccess-Part

2:SQLoption”introducedgeospatialdatainSQLin2010.– Spatiallyenableddatabases(e.g.,PostGIS,OracleSpatial,

Spatialite).

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SpatialAIResearch

• LotsofinterestingtheoreticalandpracticalworkbyArtificialIntelligenceresearchers.

• Topicscovered:– Spatiallogics– Spatialconstraintnetworks– Implementedsystems– Applications– ContributionstootherAIresearchareaslikeplanningandcommonsensereasoning

Motivation

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GeospatialDataontheWeb

• Verypopularandusefulmapsoftware.

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OpenGovernmentData

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LinkedGeospatialData-OrdnanceSurvey(UnitedKingdom)

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LinkedGeospatialData-Kadaster(TheNetherlands)

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OpenStreetMap

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http://www.linkedopendata.gr

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LODCloud(Aug.2014):LotsofGeospatialData

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LODCloud(Aug.2017):LotsofGeographyData

GeospatialExtensionsofRDFandSPARQL

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Overview

• Earlypapers:– Kolas(2007)– Perry’sPhDdissertation(2008)– KoubarakisandKyzirakos(2010)

• Morerecentproposals:– TheOGCstandardGeoSPARQL(2012)– ThedatamodelstRDF/stSPARQL(2012)– TheframeworkRDFi(2013)

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GeoSPARQLandstRDF/stSPARQL

• Thetwoproposalsofferconstructsfor:– Developingontologiesforspatialandtemporaldata

– EncodingspatialandtemporaldatathatusetheseontologiesinRDF

– ExtendingSPARQLtoqueryspatialandtemporaldata

• TemporaldataiscoveredonlybystRDF/stSPARQL

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[PerryandHerring,2012]GeoSPARQL

GeoSPARQLisanOGCstandard.Mainfunctionalities:• RepresentinggeospatialinformationisdoneusinghighlevelontologiesinspiredfromGISterminology

• Geometriesarerepresentedusingliteralsofspatialdatatypes

• LiteralsareserializedusingOGCstandardsWKTandGML

• Familiesoffunctionsareofferedforqueryinggeometries

Core

Topology VocabularyExtension

- relation family

Geometry Extension - serialization - version

Geometry TopologyExtension

- serialization - version - relation family

Query Rewrite Extension


RDFS Entailment Extension


Parameters• Serialization

• WKT• GML

• RelationFamily• SimpleFeatures• RCC-8• Egenhofer

GeoSPARQLComponents

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GeoSPARQLCore

• Definestwotoplevelclassesthatcanbeusedtoorganizegeospatialdata

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GeoSPARQLGeometryExtension

• Providesvocabularyforassertingandqueryingdataaboutthegeometricattributesofafeature

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gag:Olympia

rdf:type gag:MunicipalCommunity; gag:name "Ancient Olympia"; gag:population "184"^^xsd:int; geo:hasGeometry ex:polygon1.

ex:polygon1

rdf:type geo:Geometry; geo:asWKT "http://www.opengis.net/def/crs/OGC/1.3/CRS84 POLYGON((21.5 18.5,23.5 18.5,

23.5 21,21.5 21,21.5 18.5))" ^^sf:wktLiteral.

Example

AncientOlympia

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GeoSPARQLGeometryExtension(cont’d)Thefollowingnon-topologicalqueryfunctionsfromthe“OpenGISSimpleFeatureAccess”standardarealsooffered:

▪ geof:distance ▪ geof:buffer ▪ geof:convexHull ▪ geof:intersection ▪ geof:union ▪ geof:difference ▪ geof:symDifference ▪ geof:envelope ▪ geof:boundary

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SELECT ?r ?cWHERE { ?r rdf:type clc:Region; geo:hasGeometry ?rGeom; clc:hasCorineLandCover ?f. ?f rdfs:subClassOf clc:Forest. ?c rdf:type gag:MunicipalCommunity; geo:hasGeometry ?cGeom. FILTER(geof:distance(?rGeom,?cGeom,uom:metre) < 1000)}

Findforestsnearmunicipalcommunities.

ExampleQuery

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GeoSPARQLGeometryTopologyExtension(cont’d)Thefollowingtopologicalqueryfunctionsfromthe“OpenGISSimpleFeatureAccess”standardareoffered:

▪ geof:sfEquals ▪ geof:sfDisjoint ▪ geof:sfIntersects ▪ geof:sfTouches ▪ geof:sfCrosses ▪ geof:sfWithin ▪ geof:sfContains ▪ geof:sfOverlaps

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SELECT ?r ?cWHERE { ?r rdf:type clc:Region; geo:hasGeometry ?rGeom; clc:hasCorineLandCover ?f. ?f rdfs:subClassOf clc:Forest. ?c rdf:type gag:MunicipalCommunity; geo:hasGeometry ?cGeom. FILTER(geof:sfTouches(?rGeom,?cGeom))}

Findforeststhatbordermunicipalcommunities.

ExampleQuery

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GeoSPARQLGeometryTopologyExtension(cont’d)• Thepreviousfamilyoffunctionsarebasedonthe

DE-9IMmodelstudiedbyClementiniandFelice.

• Similarly,thefamilyoffunctionsintheEgenhofer

andRCC-8frameworksareoffered.

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GeoSPARQLTopologyVocabularyExtension• Thisextensionisusedforrepresentingtopologicalinformationabout

features.• Topologicalinformationisinherentlyqualitativeanditisexpressedin

termsoftopologicalrelations(e.g.,containment,adjacency,overlapetc.).

• Topologicalinformationcanbederivedfromgeometricinformationoritmightbecapturedbyassertingexplicitlythetopologicalrelationsbetweenfeatures.

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TopologicalRelations

• The topological relations of the “OpenGIS Simple Feature Access” standard are offered.

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TopologicalRelations(cont’d)

• Similarly,thetopologicalrelationsoftheEgenhofer

andtheRCC-8framework.

• GeoSPARQLoffersusvocabularyforexpressingthese

topologicalrelationsinthedatabaseandthequeries.

gag:Olympia rdf:type gag:MunicipalCommunity.

gag:OlympiaMunicipality rdf:type gag:Municipality.

gag:WesternGreece rdf:type gag:Region.

gag:Olympia geo:sfWithin gag:OlympiaMunicipality. gag:OlympiaMunicipality geo:sfWithin gag:WesternGreece.

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Example

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Findthemunicipalitythatcontainsthecommunityof

AncientOlympia.

SELECT ?m

WHERE {

?m rdf:type gag:Municipality.

?m geo:sfContains gag:Olympia.

}

QueryI

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gag:OlympiaMunicipality

Answer

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FindtheregionofGreecethatcontainsthecommunity

ofAncientOlympia.

SELECT ?m

WHERE {

?m rdf:type gag:Region.

?m geo:sfContains gag:Olympia.

}

QueryII

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gag:WesternGreece

Answer

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QueryII(cont’d)

• TheanswertoQueryIIcanbecomputedbyreasoningaboutthetransitivityofrelationgeo:sfContains.

• TheGeoSPARQLstandarddoesnotcoversuchentailedtopologicalrelationsbetweenspatialobjects.Isthisaproblem?

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73,546,231 triples

AdministrativeGeographyofGreatBritain

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9,896,532triples

GlobalAdministrativeAreas(GADM)

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316,246triples

NomeclatureofTerritorialUnitsforStatistics(NUTS)

PendingExtensioninschema.org

• Topologicalrelationsbetweenplacesinschema.org

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KnowledgeGraphswithGeospatialInformation• Current extension of Yago2 with geospatial

information including topological relations between geo-entities.

TheQueryRewriteExtension

• Enablesthetranslationofqualitativetopologicalinformationappearinginaquerytoquantitative.

• Thisisdonebyrewritingofquerieswithtriplepatternsinvolvingtopologicalrelationsintoquerieswithtopologicalfunctionsongeometries.

• TherewritingisbasedonasetofRIFrulesdefinedinthestandard.

TheRDFSExtension

• EnablesstandardRDFSreasoningforGeoSPARQLclassesandproperties.

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[Kyzirakos,Karpathiotakis&KoubarakisISWC2012]TheDataModelstRDF

• AnextensionofRDFfortherepresentationofgeospatialinformationthatchangesovertime.

• Geospatialdimension:– Spatialdatatypesareintroduced.– Geospatialinformationisrepresentedusingspatialliterals

ofthesedatatypes.– OGCstandardsWKTandGMLareusedfortheserialization

ofspatialliterals.• Temporaldimension• Proposedindependentlyandaroundthesametimeas

GeoSPARQL(startingwithanESWC2010paperbyKoubarakisandKyzirakos).

• ItisanextensionofSPARQL1.1• Itoffersfamiliesoffunctionsforqueryinggeometries.The

samefunctionsasintheGeometryExtensionandGeometryTopologyExtensionofGeoSPARQL.

• Inadditionthefollowingspatialaggregatefunctionsareoffered:

• Temporaldimension(notcoveredinthistutorial.SeetheESWC2013byBereta,SmerosandKoubarakis).

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strdf:geometry strdf:union(set of strdf:geometry A) strdf:geometry strdf:intersection(set of strdf:geometry A) strdf:geometry strdf:extent(set of strdf:geometry A)

TheQueryLanguagestSPARQL

GeoSPARQLvs.stSPARQL Core

Topology VocabularyExtension

- relation family

Geometry Extension - serialization - version

Geometry TopologyExtension


Query Rewrite Extension


RDFS Entailment Extension


sSPARQL

ExampleofstSPARQLComputethepartsofburntareasthatlieinconiferousforests.

SELECT ?burntArea (strdf:intersection(?baGeom,

strdf:union(?fGeom)) AS ?burntForest)

WHERE { ?burntArea rdf:type noa:BurntArea;

strdf:hasGeometry ?baGeom.

?forest rdf:type clc:Region;

clc:hasLandCover clc:ConiferousForest;

strdf:hasGeometry ?fGeom.

FILTER (strdf:intersects(?baGeom,?fGeom)) }

GROUP BY ?burntArea ?baGeom

Geospatialdescriptionlogicsandgeospatialontology-baseddataaccess

Motivation

• PublishingdataasRDFandcorrelatingthemwithlinkedgeospatialdataisuseful

• Challenges:– Domainexperts(earthscientists,geologists,etc.)anddomain

specificapplicationsheavilyrelyongeospatialdatabases

– Originaldataarestoredinthem

– ConversiontoRDFisnotalwayspractical• Frequentupdates

• Largedatasets

• Differenttoolsneedtobeused

Domainexperts☹

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RepresentingGeospatialInformationinDescriptionLogics• UseOWL-DL[Katzetal.2005]• Defineaspatialconcrete-domainDL

– [LutzandMilisic,2007]– [ÖzçepandMöller,2012]

• UseOWLandaspatialABOX– RacerPro[Wessel-Möller,2009]– PelletSpatial[StockerandSirin,2009]– [Grütteretal.,2008]

• KeywordqueriesoverspatialOBDAsources[Eiteretal.2013]• Spatialontology-mediatedqueryansweringovermobilitystreams

[Eiteretal.2017]

GeospatialOntology-basedDataAccess

• GeospatialRDB2RDFsystems:GeoTriples,TriplesGeo

• Mappinglanguages:R2RML(W3Cstandard),OBDA • OBDAsystems:– Ontop[Rodriguez-Muroetal.,JWS’15]– Ultrawrap[Sequedaetal.,JWS’13]

• GeospatialOBDAsystems:– Ontop-spatial[Bereta&Koubarakis,ISWC’16]– OracleSpatialandGraph12crelease2

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OBDAMappings[MappingDeclaration][[mappingIdgag_geometry

targetgag:geometry/{gid}/gag:asWKT{geo}^^geo:wktLiteral.

sourceselectdistinctgid,geomfromgag

mappingIdclc_geometry

Targetclc:/{gid}/clc:hasGeometryclc:/geometry/{id}/.clc:/{gid}/clc:asWKT{geom}^^geo:wktLiteral.

sourceselectdistinctgid,geomfromclc

mappingIdclc_id

targetclc:/{gid}/clc:hasID{gid}.clc:/{gid}/clc:hasLandUse{code_00}.

sourceselectdistinctgid,geom,code_00fromclc

mappingIdclc_type

targetclc:/{gid}/clc:typeclc:type.clc:/{gid}/rdf:typeclc:Area.

sourceselectdistinctgid,geomfromclc]]

R2RMLexample

[arr:TriplesMap;

rr:logicalTable[arr:R2RMLView;

rr:sqlQuery"selectdistinctgid,geomfromgag"];rr:predicateObjectMap[arr:PredicateObjectMap;

rr:objectMap[arr:ObjectMap,rr:TermMap; rr:column"geo";

rr:termTyperr:Literal]; rr:predicateclc:asWKT];

rr:subjectMap[arr:TermMap,rr:SubjectMap; rr:templategag:{gid};rr:termTyperr:IRI]].

VirtualTriples

clc:20440rdf:typegeo:Geometry;geo:asWKT“POLYGON(…)”^^geo:wktLiteral.Clc:20512rdf:typegeo:Geometry;geo:asWKT“POLYGON(…)”^^geo:wktLiteral.…

ExampleGeoSPARQLquerySelectCORINEareas,theirlanduseandtheadministrativedivisiontheybelongto.

PREFIXgeo:<http://www.opengis.net/ont/geosparql#>PREFIXgag:<http://geo.linkedopendata.gr/gag/ontology/>PREFIXclc:<http://geo.linkedopendata.gr/corine/ontology#>

SELECTDISTINCT?x1?x2?luWHERE{?x1geo:asWKT?g1.?x2geo:asWKT?g2.?x2clc:hasLandUse?lu.FILTER(geof:sfIntersects(?g1,?g2))}

http://www.opengis.net/ont/geosparql

http://geo.linkedopendata.gr/gag/ontology/

http://geo.linkedopendata.gr/corine/ontology

GeoSPARQL-to-SQLtranslationGeoSPARQL query

Datalog spatially-enabled program

Spatial SQL query

Geospatial DBMS

….

SELECT ?x1 ?x2 WHERE{ ?x1 geo:asWKT ?g1 . ?x2 geo:asWKT ?g2 . FILTER (geof:sfOverlaps(?g1,?g2)) }

SELECT?x1?x2WHERE{?x1geo:sfOverlaps?x2}

OR

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Spatial SQL query

Geospatial DBMS

….

ans1(x1,g1) :- ans2(g1,g2,x1,x2)ans2(g1,g2,x1,x2) :- ans4(g1,g2,x1,x2), SF-OVERLAPS(g1,g2)ans4(g1,g2,x1,x2) :- ans8(g1,x1), ans9(g2,x2)ans8(g1,x1) :- http://www.opengis.net/ont/geosparql#asWKT(x1,g1)ans9(g2,x2) :- http://www.opengis.net/ont/geosparql#asWKT(x2,g2)

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Spatial SQL query

Geospatial DBMS

….

SELECT *FROM (SELECT DISTINCT 1 AS "x1QuestType", ... 10 AS "g1QuestType", NULL AS "g1Lang", CONCAT('<http://www.opengis.net/def/crs/EPSG/0/4326> ' , ST_AsText(QVIEW2."strdfgeo")) AS "g1" FROM geo_values QVIEW1,geo_values QVIEW2WHERE (ST_Overlaps(QVIEW2."strdfgeo",QVIEW1."strdfgeo")) ANDQVIEW1."id" IS NOT NULL ANDQVIEW1."strdfgeo" IS NOT NULL ANDQVIEW2."id" IS NOT NULL ANDQVIEW2."strdfgeo" IS NOT NULL) SUB_QVIEW

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ExampleGeoSPARQLQuery

PREFIXgag:<http://geo.linkedopendata.gr/gag/ontology/>PREFIXclc:<http://geo.linkedopendata.gr/corine/ontology#>

SELECTdistinct?x1?luWHERE{ ?x1geo:asWKT?g1. ?x2geo:asWKT?g2. ?x2clc:hasLandUse?lu. FILTER(geof:sfIntersects(?g1,?g2))}

http://geo.linkedopendata.gr/gag/ontology/

http://geo.linkedopendata.gr/corine/ontology

RasterDataSources[[mappingIdchicago

target:{rid}rdf:type:rasterCell;:hasGeometry{rast}.

sourceselectrid,rastfromchicago;

mappingIdgadm

target:{id_0}rdf:type:AdministrativeDivision;geo:hasGeometry:{gid}.

:{gid}geo:asWKT{geom}^^geo:WKTLiteral.

sourceselect*fromusa_adm2]]

DatasourcesCHICAGO[rid|rast]

USA_ADM2[gid|id_0|iso|name_0|id_1|name_1|id_2|name_2|geom]

GeoTIFFimageofChicagoimportedinPostGISastable(rastergeometries)

ShapefiledescribingUSAadministrativedivisionsandboundaries(vectorgeometries)

ExampleQueryRetrieveadministrativedivisionsthatintersectwithrastercellsoftheGeoTIFFimageofChicago.

SELECT?admWHERE{?rrdf:type:rasterCell.?r:hasGeometry?rast.?admrdf:type:AdministrativeDivision.?admgeo:hasGeometry?g.?ggeo:asWKT?geom.FILTER(geof:sfIntersects(geom,rast))

Vectorgeometrieswillbebound

Rastergeometrieswillbebound

Implementedsystems,evaluationandcomparison

Strabon(ISWC2012,ESWC2013)

stRDFgraphs

stSPARQL/ GeoSPARQL

queries

WKT GML

Findmoreat:http://strabon.di.uoa.gr

http://www.strabon.di.uoa.gr




Strabon-Geospatialfeatures

Supportfor:• stRDFandstSPARQL• GeoSPARQL(core,geometryextension,geometrytopologyextension)

• MultipleCoordinateReferenceSystems(CRS)• BuildsonSesameRDBMS• Geospatialrelationaldatabaseasback-end(PostGIS,MonetDB)

• R-treeindex

Parliament• DevelopedbyRaytheonBBNTechnologies(DaveKolas).Availableat:http://www.parliament.semwebcentral.org/

• FirstGeoSPARQLimplementation.Supports:– Core– Topologyvocabulary– Geometry– GeometryTopology– RDFentailment– MultipleCRS– R-treeindex

http://www.parliament.semwebcentral.org/



uSeekM

SpatialpluginforSesamebyOpenSahara.Supports:• GeoSPARQL– Core– TopologyVocabulary– Geometry– GeometryTopology– RDFSentailment

• NomultipleCRS.OnlyWGS84• Opensource(Apachev2.0).Availableat:https://dev.opensahara.com/projects/useekm

https://dev.opensahara.com/projects/useekm




GraphDB

• DevelopedbyOntotext.FormerOWLIM.• GeoSPARQLsupport• ApacheLuceneindex• Closedsource.Availableat:https://ontotext.com/products/graphdb/editions/

https://ontotext.com/products/graphdb/editions/




Allegrograph

• QuadstoredevelopedbyFranzInc• Closedsource.Availableathttp://www.franz.com/agraph/allegrograph/

• NoGeoSPARQLsupport• Supportsonlypoints• Onlyafewspatialoperationssupported(Buffer,BoundingBox,Distance)

http://www.franz.com/agraph/allegrograph/




OpenLinkVirtuoso

• DevelopedbyOpenLink.Availableat:http://virtuoso.openlinksw.com/Supports:

• NoGeoSPARQL• Pointsonly– Serializedastypedliterals

• Spatialoperations(subsetofSQL/MM)• MultipleCRS• R-tree

http://virtuoso.openlinksw.com/

http://virtuoso.openlinksw.com/

Stardog

• LimitedGeoSPARQLsupport:– WKTliterals.Nativesupportforpoints.UseofJTSlibraryforpolygons

– Operatorsgeof:relate,geof:distance,geof:within,geof:nearby,geof:area

– Geospatialfeaturesonlyofferedinenterpriseedition

Brodtetal.

• BuiltontopofRDF-3XbyUniversityofStuttgart• NoGeoSPARQLsupport• GeometriesrepresentedastypedWKTliterals• OnlyWGS84supported• OGC-SFAspatialoperationsasSPARQLfilterfunctions• R-treesupported(butonlyusedforspatialselections)

PerryPhDthesis

• ImplementationontopofOracle10gbyWrightStateUniversity

• SupportforSPARQL-ST• GeoRSSGMLserializationofgeometries• Spatialandtemporalvariables• Spatialandtemporalfilters(RCC8,Allen)• R-treesupport

OraclespatialandGraph

• DevelopedbyOracle• GeoSPARQLsupport• CRSsupport• RecentlyaddedsupportforvirtualRDFgraphs(asofOracleSpatialandGraph12cRelease2)

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[ESWC2016,ISWC2016]

http://ontop-spatial.di.uoa.gr

https://github.com/ConstantB/ontop-spatial






Architectureoverview(extendingOntop)

Evaluation

GeographicaBenchmark

• Evaluationofthestate-of-the-artgeospatialRDFstores[Garbisetal.,ISWC2013]– Realworkload– Syntheticworkload

• Stressesallrecentsystemsinheavilyspatialqueriesandworkload.

• OpensourceJavaframeworkavailableathttp://geographica.di.uoa.gr

http://geographica.di.uoa.gr/


Realworkload

Dataset Size #triples #geometries #points per geometry (avg)

Geonames 45MB 400K 22000 1

DBpedia 89MB 430K 8000 1

LGD 29MB 150K 12000 1

GAG 33MB 4K 325 400

CLC 401MB 630K 45000 140

Hotspots 90MB 450K 37000 4

Executiontimesinrealworkload

Nontopologicalconstructfunctions

Spatialselections

Spatialjoins

Aggregatefunctions

Addingsystemswithlimitedgeospatialfunctionalities

GeospatialRDFstoresvsOBDA

Dataset Table Size No. of rows/

geometries

Avg #points/ geometry

Corine Land Cover (CLC)

283MB 44834 187.84

Hotspots 35 MB 37048 5

Global Administrative Geography (GAG)

24 MB 326 3020.14

OSM-Buildings 42 MB 155474 6.5

OSM-Landuse 20 MB 40220 19.4

OSM-places 2.4 MB 13043 1

OSM-points 12 MB 61664 1

OSM-railways 2 MB 4996 13.3

OSM-roads 250 MB 514403 19

OSM-waterways 16 MB 20565 39.84

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QueriesHighly

selective query

Poorly selective query

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Evaluation

Ontop-spatialStrabonSystemO

Translatedqueries• Strabonquery

• Ontop-spatialquery

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Spatialjoinquery6:Strabonqueryexecution

ResultofexplainqueryvisualizedusingPgAdminIII

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DBstatisticsforspatialjoin6Strabondbstatistics Ontopdbstatistics

Tablesproducedusinghttps://explain.depesz.com/

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Operation(geof:intersects)

Selectivity Geometrytypes

Strabon Ontop-spatial Remarks

SpatialSelection high *(irrelevant) 100msecs 100msecs

SpatialSelection low Point-Polygon 100msecs 100msecs

SpatialSelection low Polygon-Polygon

500msecs 100-200msecs

SpatialJoin high Point-Polygon <1000msecs <1000msecs

SpatialJoin high Polygon-Polygon

100000msecs 100000msecs

SpatialJoin low Polygon-Polygon

>40mins 10mins Sometimesthedifferencehereis

order(s)ofmagnitude

PerformanceEvaluation:Strabonvs.Ontop-spatialona30GBdataset

PerformanceEvaluationandScalabilityofStrabonandOntop-spatial• DefinedandusedthebenchmarkGeographica(http://geographica.di.uoa.gr/).

• StrabonhasbetterperformanceandfunctionalitythanParliament,uSeekM,SystemX,Virtuoso,SystemO,andSystemY(longerversionofISWC2013paper).

• Ontop-spatialhasbetterperformancethanStrabonandSystemO(longversionofISWC2016paper).



Scalability

• StrabonandOntop-spatialcanscaleto100GBofdataandanswerqueriesinmillisecondsifthegeometriesarepointsand/ortheselectivityofthequeryishigh.

• Morecomplexgeometrieshaveanimpactonperformance.

VisualizingTime-EvolvingLinkedGeospatialData

ArchitectureFindmoreat:http://sextant.di.uoa.gr

http://sextant.di.uoa.gr

ThematicMaps

Defini\on:AthemaGcmap isatypeofmapdesignedtoshowapar~cular theme connected with a specific geographic area.These maps can portray physical, social, poli~cal, cultural,economic,sociological,agricultural,oranyotheraspectsofacity,state,region,na~on,orcon~nent.

SPARQL Endpoints Geospatial File Formats+ =

ThematicMaps

MapOntology

MapSharing

SharemapsusingmapURI,ortheloadmapmodal

Map URI: http://<domain>/Sextant/?mapid=<mapID>

TemporalDimension

StrabonDBMSandSIMILETimeline

Implementa~on of he valid ~me component of stRDF andstSPARQL in systemStrabonallowsus toqueryboth the spa~alandthetemporaldimension.Enrichingourresultswithtemporalinforma~onallowsus tocreate layerswithvalid~me.UsingtheSIMILE Timeline widget we can make these layers appear anddisappearfromthemapaccordingtotheirvalid~me.

TemporalDimensionQueryexampleinstSPARQL

PREFIXnoa:<http://teleios.di.uoa.gr/ontologies/noaOntology.owl#>PREFIXrdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>PREFIXstrdf:<http://strdf.di.uoa.gr/ontology#>PREFIXxsd:<http://www.w3.org/2001/XMLSchema#>

SELECTDISTINCT(strdf:transform(?hGeo,<http://www.opengis.net/def/crs/EPSG/0/4326>)as?geometry)?timeWHERE{ ?hrdf:typenoa:Hotspot; noa:hasAcquisitionTime?time; noa:hasGeometry?hGeo.FILTER(?time="2012-07-18T11:30:00"^^<http://www.w3.org/2001/XMLSchema#dateTime>)FILTER(strdf:within(?hGeo,"POLYGON((21.7038.23,21.7038.33,21.9138.33,21.9138.23,21.7038.23));http://www.opengis.net/def/crs/EPSG/0/4326”^^strdf:WKT))}

TemporalDimension

MapMetadata

MapRegistry

Defini\on:Mapregistries,areSPARQLendpointsthatholdallthemap informa~on and metadata to assist us in saving andretrievingthemaps.

PredefinedQueries

QueriesthatarecreatedbyanexpertandarestoresastriplesinaSPARQLendpoint.Non-expertuserscanprovidetheURLoftheendpointandgetalistofthedescriptionsofallthepredefinedqueriesavailable,thenselectoneandvisualizeitonthemap.

PredefinedQueries

StatisticalCharts

Automa~ccrea~onofchartsoveralayer’sa�ribute

StatisticalChartsEnhancementofDatasets

• TheRDFDataCubeVocabulary(W3Crecommendation).

• Definethedimensionsandthemeasuresofthedataset.

• Usetheclassesqb:DimensionProperty,qb:MeasureProperty,and

thepropertyqb:orderfromDataCubetoenhanceourschema.

• ASelf-adjustingquerytocreateallpossiblecharts.

StatisticalCharts

EnhancementofOntologySchema

StatisticalCharts

EnhancementofOntologySchemaqb:DimensionProperty

StatisticalCharts

EnhancementofOntologySchemaqb:MeasureProperty

StatisticalCharts

Self-adjus\ngQuery

StatisticalCharts

Self-adjus\ngQueryPREFIXrdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>PREFIXtf:<http://data.linkedeodata.eu/talking-fields/ontology#>SELECTDISTINCT?RasterCell?hasVigor?hasFertValue?hasCVWHERE{

?Farmrdf:typetf:Farm.?Fieldrdf:typetf:Field.?RasterCellrdf:typetf:RasterCell.?Fieldtf:belongsToFarm?Farm.?RasterCelltf:belongsToField?Field.OPTIONAL{?RasterCelltf:hasVigor?hasVigor.}.OPTIONAL{?RasterCelltf:hasFertValue?hasFertValue.}.OPTIONAL{?RasterCelltf:hasCV?hasCV.}.?Fieldrdf:type?typeField.FILTER(?Field=<http://data.linkedeodata.eu/

talking-fields/000001/Field/id/1154>&&?typeField=tf:Field).

}ORDERBY?RasterCell

http://data.linkedeodata.eu/talking-fields/ontology%23

StatisticalCharts

ChartOntology

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ChangeDetectionService

GreenCity

OpenProblems

OpenQuestions(Theory)

• ThedatacomplexityofqueryprocessingforstSPARQLandGeoSPARQLhasnotbeenstudiedsofar.

• WehavedonesoonlyfortheoriginalstSPARQLproposalbasedonconstraints(ESWC2010).

• Similarlyforotherinterestingproblemssuchasquerycontainmentetc.

• ThefoundationsofOntop-spatialdeservefurtherstudy(comparisonwiththetheoryofspatialdescriptionlogics).

OpenQuestions(Practice)

• Howcanwebuiltan(evenmore)scalablegeospatialRDFstorelikeStrabonontopofApachebigdatatechnologies?– AnalyzedtheprosandconsofusingGeoSpark,SIMBAandSpatialSpark.• GeoSparkseemstobethemostmatureandiscontinuouslybeenimprovedbyitsdevelopers.

• Howcanwehandle1012tripleswith108polygons?(thevolumeofgeospatialdataownedbyanationalcartographicagency)

OpenQuestions(cont’d)

• HowdowerepresentandqueryrasterdataontheSemanticWeb?– RasterextensionofOntop-spatial.– ArraydatabaseextensionofOntop-spatial.–Workon“CoveragesinLinkedData”bytheOGC/W3CSpatialDataontheWebworkinggroup.

Otherrelevantresearchtopicsofinterest• Naturallanguagequeryprocessingforlargegeospatialknowledgebases(e.g.,Yago2).

• Examplequeries:– FindparksinBonnclosetoFraunhoferIAIS.– FindriversthatcrosscitiesofGreeceandtheirlengthismorethan20km.

• CurrentworkinthecontextofWDAqua(AnsweringQuestionsusingWebData,aMarieSklodowska-CurieInnovativeTrainingNetwork,http://wdaqua.eu/).

http://wdaqua.eu/

http://wdaqua.eu/

Thanks!Questions?

Formore,seethewebpageofourgrouphttp://kr.di.uoa.gr.

http://kr.di.uoa.gr/

http://kr.di.uoa.gr/