1. Open Geospatial Consortium. Geography Markup Language (GML) Encoding Standard. OpenGIS Implementation Standard (2007), http://portal.opengeospatial.org/files/?artifact_id=20509
2. Open Geospatial Consortium. Geography Markup Language (GML) simple features profile. OpenGIS Implementation Standard Profile (2010), http://portal.opengeospatial.org/files/?artifact_id=39853
3. Open Geospatial Consortium. OpenGIS Implementation Specification for Geographic information - Simple feature access - Part 2: SQL option. OpenGIS Implementation Standard (2010), http://portal.opengeospatial.org/files/?artifact_id=25354
4. Open Geospatial Consortium. OpenGIS Implementation Standard for Geographic information - Simple feature access - Part 1: Common Architecture. OpenGIS Implementation Standard (2010), http://portal.opengeospatial.org/files/?artifact_id=25355
5. Open Geospatial Consortium. OGC GeoSPARQL - A geographic query language for RDF data. OGC Candidate Implementation Standard (2012)