Fully agree. A diagram is ok to describe a flow, but for complex code or systems, round tripping is a necessity, otherwise the diagram is or quickly becomes inaccurate and worse than useless.
In the 90s I tried software called TogetherJ, it seemed to support round tripping really well, so well maintaining code was the same as maintaining diagrams, and led to better quality in both, along with documentation and other benefits such as relaying higher order concepts.
I just did a search for togetherj and the only reference I could find was a 20 year old forum mention. Weird. I suppose there must be high end enterprise CASE software that still supports this approach, though I'm guessing most people abuse it so it's no longer respected.
I think these things happen in cycles, as we can 'orchestrate' larger systems with meta descriptions of components, they become more valuable.
I remember both Rational Rose and TogetherJ CASE tools. Round-trip engineering was supposed to be practiced by both Domain Experts and Programmers each modifying their models and still having them all consistent with each other. But what happened in practice was that only Programmers used them who did not see the utility of updating a UML class hierarchy instead of directly updating the Class itself. That and the exorbitant pricing is why they fell out of favour. It is really a shame because with the explosion of distributed apps using a variety of languages/tools a single uniform interface modeling all aspects of the software is sorely needed.
PS: Came across the book Software Visualization - Visualizing the Structure, Behaviour and Evolution of Software by Stephan Diehl which seems to provide a good survey of the field.
