OverCAD >> DWG

Introduction

DWG ("drawing") is a format used for storing two and three dimensional design data and metadata. It is the native format for the AutoCAD Computer Aided Design package, as well as Intellicad (and its variants), and PowerCAD. DWG is supported non-natively by several hundred other software applications.

History

DWG (denoted by the .dwg filename extension) was the native file format for the Interact CAD package, developed by Mike Riddle in the late 1970s, and subsequently licensed by Autodesk in 1982 as the basis for AutoCAD. From 1982 to 2007, Autodesk created versions of AutoCAD which wrote no less than 18 major variants of the DWG file format, none of which is publicly documented.

The DWG format, has become a de facto standard for CAD drawing interoperability. It has been estimated that there are in excess of two to four billion DWG files in existence.

Autodesk designs, defines, and iterates its DWG format as the base format of its applications. In addition to its applications being based on DWG, Autodesk provides a read/write library, called RealDWG, under selective licensing terms, for use in non-competitive applications. Several companies have attempted to reverse engineer Autodesk's DWG format, and offer software libraries which endeavor to read and write Autodesk DWG files. The Open Design Alliance, a non-profit consortium created in 1998 by a number of software developers (some of which were competitors to Autodesk), provides a read/write/view library, called DWGdirect. There are no open-source DWG libraries currently available, and neither RealDWG nor DWGdirect are licensed on terms that are compatible with the gnu gpl, or similar free software license.

In 1998, Autodesk added file verification to AutoCAD R14.01, through a function called DWGCHECK. This function was supported by an encrypted checksum and product code (called a "watermark" by Autodesk), written into DWG files created by the program. In 2006, in response to Autodesk users expereincing bugs and incompatibilities in files written by reverse-engineered DWG read/write libraries, Autodesk modified AutoCAD 2007, to include "TrustedDWG technology", a function which would embed a text string within DWG files written by the program : "Autodesk DWG. This file is a Trusted DWG last saved by an Autodesk application or Autodesk licensed application." This helped Autodesk software users ensure that the files they were opening were created by an Autodesk, or RealDWG application, reducing risk of incompatibilities. AutoCAD would pop up a message, warning of potential stability problems, if a user opened a 2007 version DWG file which did not include this text string.

On 22nd November 2006, Autodesk sued the Open Design Alliance alleging that its DWGdirect libraries infringed Autodesk's trademark for the word "Autodesk", by writing the TrustedDWG code (including the word "AutoCAD") into DWG files it created. In April 2007, the suit was dropped, with Autodesk modifying the warning message in AutoCAD 2008 (to make it more benign), and the Open Design Alliance removing support for the TrustedDWG code from its DWGdirect libraries.

In 2006, Autodesk applied for a US trademark on "DWG", as applied to software (as distinct to its application as a file format name.). In a non-final action in May, 2007, the examining attorney refused to register the mark, as it is "merely descriptive" of the use of DWG as a file format name (for which Autodesk does not claim any trademark rights.) In September, 2007, Autodesk responded, claiming that DWG has gained a "secondary meaning," separate from its use as a file format name. As early as 1996, Autodesk has disclaimed exclusive use of the DWG mark in US trademark filings.