Wikipedia's open and see what they write about formats .DXF and .DWG and their development.

DXF - open file format for the exchange of information between the graphical CAD applications. Was first introduced in December 1982 as part of AutoCAD 1.0, as a data exchange format that provides the same information as the enclosed format AutoCAD - DWG, specification of which have never enjoyed.

In "Drawings in SVG format. Part 2 - Draft Standard" an example of drawing simple graphics from CAD systems. In the continuation we consider drawing hatching for different materials.