AEC Tech News #96 (Apr. 24, 2003)

23 Apr, 2003 By: Lachmi Khemlani

This issue of the AEC Tech newsletter continues with the discussion on the recent BIM debate between Autodesk and Bentley that was started in the last issue. Autodesk was represented in the debate by Phil Bernstein, vice president, Building Solutions Division, while Bentley was represented by Keith Bentley, cofounder and co-CTO of the company. The debate was produced and moderated by Jerry Laiserin, editor and publisher of The LaiserinLetter (

We saw in the last issue how both sides were in agreement over the importance of BIM and its potential benefits to the industry, but they differed radically on how a BIM solution should be implemented. Autodesk believes that the building data should be centralized and integrated, whereas Bentley believes the data should not be centralized and will be distributed across multiple applications. These different viewpoints stem directly from the fact that the centerpiece of Autodesk's BIM strategy is a tool, Revit, while that of Bentley's is a platform, MicroStation. Moreover, Autodesk is advocating a revolutionary approach to BIM by urging its users to switch to Revit, while Bentley is advocating an evolutionary approach based on its existing MicroStation platform and Triforma applications. Autodesk will continue to develop and support both AutoCAD and ADT, so it is not denying the evolutionary approach to those users who want it, but it is undeniably pushing Revit as its BIM solution of the future.

This issue of the AEC Tech newsletter looks at the differences on the interoperability issue that emerged from the debate, and concludes with my overall analysis of it.

Different Perspectives on Interoperability

The debate brought into focus the substantial differences between the two companies on issues related to file formats, compatibility, and interoperability between multiple applications. Two questions along these lines were posed to the debaters.

How can authors of BIM data be assured that the data they create will be easily understandable and accessible to all existing and future applications that need to use that data?

Both vendors are members of the International Alliance for Interoperability (IAI), which is now part of the National Institute of Building Sciences (NIBS). What is their view of interoperability initiatives such as the IFC (Industry Foundation Classes) and aecXML, developed and managed by the IAI, and how do these relate to their BIM product offerings?

In response to the first question, Keith Bentley emphasized the openness of MicroStation's native DGN format, the ability of MicroStation V8 to directly work with DWG files, and Bentley's involvement with the OpenDWG Alliance to promote open file formats, as its commitment to interoperability. In contrast, Phil Bernstein stressed that Autodesk was more interested in functionality and on making the best possible models for BIM rather than in the openness/closeness issue. What Autodesk thinks is critical is the interface between the model and the specific applications that need to interface with it to get the BIM data they need from the model. The connection strategy to this data has to be designed; just throwing open the whole model or file format isn't the answer.

With regard to IFC and aecXML, Bentley participates in both efforts and will continue to support them in the foreseeable future. While Autodesk also participates in both efforts, Bernstein expressed his belief that the IFC was trying to solve the problem ahead of the technology that was available. Autodesk will be committed to IFC to the extent that its customers are interested in it, and it has found that this interest is only moderate in North America. He thought there should be more options for how applications interconnect, in addition to IFCs, such as ODBC compliance (as in Revit), APIs (as in AutoCAD and ADT), and so on.

A major bone of contention that emerged from the Bentley side was Autodesk's encryption of the revamped DWG file format in the latest release of AutoCAD, 2004. Keith Bentley strongly felt that encryption between the owner and the data impedes free flow of information, and goes against the concept of BIM. This irk is understandable, considering that one of the most noted features in MicroStation V8 was its ability to let users work directly with AutoCAD DWG files without translating them. This functionality will no longer work with DWG files created by AutoCAD 2004. While Autodesk's encryption strategy is obviously designed to keep data proprietary, Phil Bernstein denied that the issue had any relevance to BIM, as AutoCAD was primarily a drafting solution and DWG a drawing format. Autodesk doesn't believe in simply throwing open the file format for anyone to do what they will; instead, it provides ports to the data so that applications can get the specific information they need without worrying about the rest of the model.

To summarize the interoperability perspectives of the two vendors, Autodesk believes in providing designed interconnections to the building model data contained in its applications, whereas Bentley is advocating open file formats to promote free exchange of building data between applications from different vendors.


So is the AEC industry ready for a revolution? Are AEC professionals open to change? Will they give up the drawing-based modes of practice they have spent decades perfecting? It seems to me that the answer hinges a great deal on how well Autodesk's push to promote Revit among its exiting customer base succeeds, which in turn depends upon how well the application currently performs as well as how it evolves in the future. Being a new application developed with modern programming concepts and sophisticated parametric technology, Revit has an undoubted edge over competing applications in how well it represents building components and their interrelationships. (For a detailed overview of Revit, see Issue #72: The application encapsulates a significant amount of intelligence about a building that makes it easy to use; at the same time, the encoding of many relationships can slow down its speed and cause significant challenges when dealing with large building designs. In that respect, the jury on Revit is still out, and its success can only be gauged after wide scale implementation on large projects.

As Bentley is advocating an evolutionary approach, its customers don't necessarily have to do anything different. They can continue doing CAD and not BIM, using MicroStation and its TriForma suite of building applications, if that is what they want. In contrast, professionals wouldn't switch to Revit if they still wanted to do CAD, so the success of Revit will play a significant role in the future of BIM.

Using the same rationale, I would also say that the issue of interoperability will become more or less critical depending on how well Autodesk's BIM strategy plays out. If Revit proves itself as an effective, efficient, and intelligent BIM tool, Autodesk's "designed interconnections" approach will prevail over the "open file format" approach, and interoperability efforts such as IFC will lose ground. Otherwise, openness and interoperability will gain momentum, and we could even see non-proprietary building model alternatives to IFC that are developed with newer and superior data modeling principles.

As for the debate itself, I was a little disappointed that nothing fundamentally new was said that we haven't heard before. Neither party addressed the issue of how BIM integrates all the diverse building disciplines, and what specific technologies they have to ensure that the BIM data model is used throughout the building lifecycle--not just for architectural design, but also for structural, mechanical, electrical, and plumbing design, construction and project management, facilities management, and operation and maintenance. There was also no discussion of how their online collaboration solutions, Autodesk's Buzzsaw and Bentley's Viecon, need to be different to work with the BIM concept rather than the CAD concept.

Coming Up Next

In addition to Autodesk and Bentley, there is a serious third contender in the BIM race, Graphisoft, whose 20-year-old solution, ArchiCAD, has had building modeling capabilities from the start. The next issue of the AEC Tech newsletter will be devoted to a discussion of Graphisoft's perspective on BIM.

Relevant Links

Debate Webcast archive and BIM discussion/commentary:



OpenDWG Alliance:

IFC documentation: