Hi Reynold and Daniel,
Thank you for your comments. I hear what you are saying, I also want this lean and clean - it is just a question where we hide the mess, haha.
So, I can see we have different understandings of the Amazing Technicolour Dream Triangle of Interoperability™ 
We are trying to co-create a structural schema that will allow seamless interoperability between the different structural software packages, that being BIM, FE or section checks, right? If I’ve misunderstood that then all good - I’ll just stick everything in the green layer in my own branch.
If the purple layer is the “standard”, e.i. the structural schema, the important thing would be that there is no conflict between software packages, so if I stream a cruciform profile to both GSA and ETABS it stays a cruciform profile and isn’t changed to a triangle in one of them. It might be changed to an explicit profile representing the cruciform shape but not a triangle.
There’s therefore nothing wrong with having a lot of stuff in the purple layer, as long as it is not conflicting with something. In a very idealised world, we would want everything to be in the purple layer, no? Raymond, I think I would therefore have to disagree with the way you interpret the definition that the purple layer is “minimum information required”. Minimum information required is the minimum agreeable information, in the example of the cruciform that is the shape - if some programs then define that as an explicit list of points or as two flanges and two webs then that is no longer minimum information but a software-specific way of defining it. But, to me, just because all software packages doesn’t include a definition for cruciform does not mean that it doesn’t belong in the purple layer.
What would you suggest as the alternative? Consider two scenarios for streaming a cruciform profile:
- From Software A that can handle cruciform to Software B that doesn’t know what a cruciform is
- From Software A that can handle cruciform to another Software C that can handle cruciform
I would say that 1) can be solved by having a conversion to explicit in place for Software B that doesn’t recognise cruciform. I would say that it would be a loss of information if I for 2) needed to convert to explicit because cruciform wasn’t allowed in the purple layer, and it would be less lean overall solution if I had to rely on catching this scenario and convert to my own schema in the green layer, just to avoid loss of information, but for other scenarios where I have a rectangle profile I do not rely on my green layer schema.
Then I also think that we need to exactly consider the whole workflow, not just the FE interoperability. I again have to disagree that the purple layer is only for FE analysis software, no it should consider all aspects of a structural engineering workflow and section design is a big part of that. I want to be able to pick up a stream with results and run section analysis on it automatically in the cloud.
All that said (sorry got a bit long), I am up for finding a solution that works for all of course.
Best, Kristjan