DAT files can reference other DAT files, so a complex brick can be built up from simpler pieces. A regular brick DAT file, for example, might reference another DAT file that represents the studs, or bumps, on the brick. A Lego model DAT file is built by referencing the individual brick DAT files that make up the model. Let's look at a simple example. You can pretty much figure it out by looking at it.
Every line has a type, which is just a number at the beginning of the line.
A 0 indicates a comment line, something that adds information to the DAT file but doesn't add to the model itself. The two important lines begin with a 1, which imports another DAT file into the model. In this case we're using 3020.DAT , the 2 x 4 plate, and 3700.DAT , the two-stud Technic brick with the hole through it. Those show where the imported part should be placed and how it should be rotated relative to the model. The DAT files for bricks are named according to their part numbers.