The article was clearly introducing the Spatial Data Format (SDF). The .sdf can provide fast spatial query through LAN/ WAN, doesn't need any RDBMS system to support. Although the .sdf was designed by Autodesk for several years ago. The .sdf3 is the multiple feature classes in one file. The Autodesk Map 3D can directly access and modify the .sdf on-the-fly and publish to MapGuide. full article