Database Structure
It is helpful to see the organization of the AutoCAD Database. There are the Symbol tables that have been in AutoCAD drawings sense Release 12 of AutoCAD. These symbol tables are used for elements such as layers and Linetypes. The Block Table contains Model and Paperspace as well as other Blocks. These blocks which are BlockTableRecords in the API contain the entities that you see rendered in the AutoCAD editor. The Named Object Dictionary contains dictionaries that were introduced in a later releases of AutoCAD. New functionality that it is added in AutoCAD use the Named Objects Dictionary. Examples of this are Layouts and PlotSettings. The database also has variables that are unique to the drawing.