The release of Geography Markup Language (GML) 3.0 in 2003 greatly increased the scope of applications that GML could deal with by adding components to support realtime sensors, coverages (including imagery), topology, time and dynamic features as well as adding a large number of new geometric types. As a result, GML now is beingapplied to many real-world problems, including resource management, intelligent transportation systems, nautical charting and census data management.
At the same time, the increase in scope has resulted in an increase in the volume and complexity of the GML specification and associated schemas. This makes implementing GML somewhat daunting for developers and vendors who are new to the technology, especially if they're new to Extensible Markup Language (XML).
Download the PDF file: GeoWorld-Profiles Make GML Easier to Swallow September 2005.pdf