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GeoServer application schema support: complex features for the masses

Ben Caradoc-Davies <Ben.Caradoc-Davies@csiro.au> CSIRO Earth Science and Resource Engineering Free and Open Source Software for Geospatial Sydney, Australia, 20-23 October 2009. GeoServer application schema support: complex features for the masses. GeoServer.

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GeoServer application schema support: complex features for the masses

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  1. Ben Caradoc-Davies <Ben.Caradoc-Davies@csiro.au> CSIRO Earth Science and Resource Engineering Free and Open Source Software for Geospatial Sydney, Australia, 20-23 October 2009 GeoServer application schema support: complex features for the masses

  2. GeoServer • Java servlet for OGC Web Services • WMS, WFS, WFS-T, ... • Open Source (GPL) • Built on GeoTools (LGPL) • Reference OGC Web Feature Service implementation • Originally supported only simple features • app-schema adds complex feature WFS (only)

  3. Simple Feature • Flat XML representation of one database table

  4. Simple Feature <sf:GSML_MAPPEDFEATURE_SIMPLE gml:id="GSML_MAPPEDFEATURE_SIMPLE.fid-5d4a2c41_12451bfad2f_-7fff"> <sf:SITE_ID>209589</sf:SITE_ID> <sf:GML_NAME>urn:cgi:feature:PIRSA:MappedFeature:209589</sf:GML_NAME> <sf:DESCRIPTION>SEE PLAN 68-611</sf:DESCRIPTION> <sf:OBSERVATION_METHOD>(DISUSED) Map Plot</sf:OBSERVATION_METHOD> <sf:OBSERVATION_METHOD_CODESPACE>urn:cgi:classifierScheme:PIRSA:ObservationMethod</sf:OBSERVATION_METHOD_CODESPACE> <sf:SPECIFICATION_URN>urn:cgi:feature:PIRSA:MineralOccurrence:43deposit</sf:SPECIFICATION_URN> <sf:LOCATION> <gml:Point srsName="urn:x-ogc:def:crs:EPSG:4283"> <gml:pos>-26.8760644 133.0181594</gml:pos> </gml:Point> </sf:LOCATION> <sf:POS_ACC>urn:ogc:def:nil:OGC::missing</sf:POS_ACC> <sf:POS_ACC_UOM>http://urn.opengis.net/</sf:POS_ACC_UOM> </sf:GSML_MAPPEDFEATURE_SIMPLE> • Type autogenerated by GeoServer • All properties in one namespace • Database schema exposed to consumer • Meaning implied by element names • Semantics often have to be inferred by user

  5. Complex Feature • Nested XML representation of multiple related database tables

  6. Complex Feature <gsml:MappedFeature gml:id="gsml.mappedfeature.209589"> <gml:description>SEE PLAN 68-611</gml:description> <gml:name codeSpace="http://services.auscope.org/pirsa-earthresource/wfs">urn:cgi:feature:PIRSA:MappedFeature:209589</gml:name> <gsml:observationMethod> <gsml:CGI_TermValue> <gsml:value codeSpace="urn:cgi:classifierScheme:PIRSA:ObservationMethod">(DISUSED) Map Plot</gsml:value> </gsml:CGI_TermValue> </gsml:observationMethod> <gsml:positionalAccuracy> <gsml:CGI_TermValue> <gsml:value codeSpace="http://urn.opengis.net/">urn:ogc:def:nil:OGC::missing</gsml:value> </gsml:CGI_TermValue> </gsml:positionalAccuracy> <gsml:samplingFrame xlink:href="urn:cgi:feature:CGI:EarthNaturalSurface" /> <gsml:specification xlink:href="urn:cgi:feature:PIRSA:MineralOccurrence:43deposit" /> <gsml:shape> <gml:Point> <gml:pos>133.0181594 -26.8760644</gml:pos> </gml:Point> </gsml:shape> </gsml:MappedFeature> • Represents object relationships • Types defined in GML application schema • Meaning specified in community-agreed information standard

  7. Why Complex Features? • Simple features: • Represent database table as XML • Interoperability through simplicity • Complex features: • GML application schema defines complex types • Represent object relationships • Polymorphism, aggregation, inheritance • Extensible information model • Scales to large problems and communities

  8. GML Application Schema Examples • GeoSciML: a GML application schema for the exchange of geoscience data • http://www.geosciml.org/ • EarthResourceML extends GeoSciML • http://www.earthresourceml.org/ • Observations and Measurements • SensorML • CityML

  9. Example: AuScope Discovery Portal • Three Australian jurisdictions: • Victoria (GSV) – deegree • Tasmania (MRT) – GeoServer app-schema • South Australia (PIRSA) – GeoServer app-schema (hosted by CSIRO) • EarthResourceML (derived from GeoSciML) • Interoperability through complex feature types defined in a GML application schema • Community-agreed information standard

  10. http://portal.auscope.org/

  11. History of GeoServer app-schema • 2005-2007: GeoServer community-schemas • Rob Atkinson, Gabriel Roldán • Geochemistry roadshow (CSIRO) • Fork of a branch (not dead, just sleeping) • Informed GeoAPI and GeoTools development • 2008: ported to trunk by AuScope • Renamed Geoserver app-schema • Now: plugin for GeoServer 2.0-beta2 and later

  12. How app-schema works • Built on GeoTools data stores • Maps simple features into complex features • Works both ways, so supports queries

  13. Installation and Configuration • app-schema plugin for vanilla GeoServer • Can coexist with simple feature types • Configure by hand-editing XML mapping files • Driven by GML application schema • Define schema URL in mapping file • Feature chaining: • Define feature types separately and use as properties of each other

  14. Mapping File • Defines mappings: • From: column in database • To: XPath in encoded XML • Use CQL expressions • Set XML attributes <AttributeMapping> <targetAttribute>gsml:observationMethod/gsml:CGI_TermValue/gsml:value</targetAttribute> <sourceExpression> <OCQL>OBSERVATION_METHOD</OCQL> </sourceExpression> <ClientProperty> <name>codeSpace</name> <value>OBSERVATION_METHOD_CODESPACE</value> </ClientProperty> </AttributeMapping>

  15. Feature Chaining • Define feature types separately • Use features as properties of each other • Simplifies configuration • Equivalent to a foreign key reference <AttributeMapping> <targetAttribute>gsml:occurrence</targetAttribute> <sourceExpression> <OCQL>OCCURRENCE_URN</OCQL> <linkElement>gsml:MappedFeature</linkElement> <linkField>gml:name</linkField> </sourceExpression> </AttributeMapping>

  16. Strengths • No XSLT programming • Configurable through straightforward mapping • Uses existing GeoTools/GeoServer components • JDBC data sources: PostGIS, Oracle, ArcSDE • Shapefiles, property files • Good performance • Strong developer community and user base • Aids adoption of GML application schemas

  17. Weaknesses • No XSLT programming • No data-driven polymorphism • Type of each property fixed at mapping time • No configuration web interface • Hand-edit XML files • Tedious and error-prone • Requires knowledge of application schema • Requires understanding of GML encoding rules

  18. Future Work • Support for data-driven polymorphism • Configuration web interface • Aid navigation of GML application schema

  19. Conclusion • Complex feature types: • Defined in a GML application schema • Represent object relationships • Extensible information model • Community-agreed information standard • GeoServer app-schema plugin: • Reuses existing community-supported components • Configured with XML mapping files • Maps simple features into complex features

  20. Resources • GeoServer User Manual: Application Schema Support • http://docs.geoserver.org/trunk/en/user/data/app-schema/ • Application Schema Support: Tutorial • http://docs.geoserver.org/trunk/en/user/data/app-schema/tutorial.html • GeoServer app-schema development • https://www.seegrid.csiro.au/twiki/bin/view/Infosrvices/GeoserverDevelopment • PIRSA EarthResource GeoServer • https://twiki.auscope.org/twiki/bin/view/Grid/PirsaEarthResourceGeoserver • AuScope Discovery Portal • http://portal.auscope.org/

  21. Credits • Rini Angreani, co-maintainer of app-schema and author of app-schema feature chaining. • Rob Atkinson, Gabriel Roldán, Jody Garnett, Justin Deoliveira, and the rest of the GeoTools and GeoServer communities. • Simon Cox, and the rest of the GeoSciML community. • CSIRO is Australia's national science agency. • AuScope Ltd is funded under the National Collaborative Research Infrastructure Strategy (NCRIS), an Australian Commonwealth Government Programme.

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