The current Soil Data Access Web Map Service (WMS) supports Open Geospatial Consortium (OGC) WMS version 1.1.1 requests while the current Soil Data Access Web Feature Services (WFS) support OGC WFS version 1.1.0 (GML2/GML3) requests. GML is an acronym for Geography Markup Language, and is the XML grammar defined by the Open Geospatial Consortium (OGC) to express geographical features. GML serves as a modeling language for geographic systems as well as an open interchange format for geographic transactions on the Internet. EPSG is an acronym used throughout the Soil Data Access web pages. It stands for European Petroleum Survey Group. They publish a database of coordinate system information plus some very good related documents on map projections and datums.