The Three-Pronged Fork in the Road

By Christian Kelley

A couple weeks back, I participated as a panelist on a Design News webcast – “A Fork in the Road in 3-D CAD Modeling” with Blake Courter of SpaceClaim and Paul Hamilton of PTC. It was an interesting call, because our perspectives are all a bit different (mine of course being the correct one wink ).

The webcast was trying to answer which 3-D modeling approach works best for you. The trouble with defining these approaches is folks still want to lump them in two categories: history-based or history-free. But there are not TWO technologies; there are now THREE technologies: history-based, history-free and synchronous.

To understand what I mean, you kind of have to look at how we arrived where we are today. Clearly a few years back, when synchronous technology began, Siemens PLM Software had thriving history-based products with direct editing capabilities, in both NX and Solid Edge. And the history-free products on the market had not lit the world on fire. In fact, all evidence was that history-based had “won” the CAD war. But we got to asking ourselves:

Is that all there is? Are we really done?

Will we still be doing history-based modeling 20 years from now?

Surely there has to be a better way?

And to start thinking about better ways, we started with what we had in the market today. What was good about history-based? What was not so good? What was good about history-free? What was not so good? The following are actual internal development slides from a few years back (never before published) that outline some of the pros and cons of each.



And of course, when we took this cold hard look at the facts, we concluded that we were indeed NOT done and there was much work to be done. We could, in fact, build something that was better than both by incorporating the good of each while leaving as much of the bad behind as possible. The chart below depicts this a bit more clearly. The things to the outside are less desirable and the things near the center are more desirable.


The way to think about this is more about end-user benefits, not technological hoopla. Who wants technology for technology sake – we need to develop technologies based on benefits to the end user. And there are some super-good things about history-based modeling. Likewise, there are some great things about non-history based. But why should you, as the user, have to choose – why can’t the darn CAD companies figure out a way to do all the good stuff?

And that is indeed the goal of synchronous technology. That you don’t need to choose between the modeling approaches anymore. There is absolutely no reason you can’t have fully dimension-driven parametric modeling, but without the burden of a linear regeneration tree – it’s just a matter of a great deal of invention and a lot of hard work.

Are we done? No – the technology is very comprehensive and capable of even more than is being demonstrated right now. For example, Sheet Metal design can benefit directly from synchronous technology and eliminate a great deal of the pre-planning required, particularly with the whole “inside/outside” management issue that sheet metal has. We are working on this even as we speak – coming soon to a theater near you!

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This article first appeared on the Siemens Digital Industries Software blog at