[dwb]

I can certainly see the appeal of number four, but on more than a couple of systems I've worked on, it would have blown up the amount of data stored in a fair proportion of tables for very questionable benefit. It's a good technique to call out, but is it really right to dictate it for everything?

And what is people's opinion of the reverse: source-of-truth in traditionally-modelled mutable relational tables, with a change log written out with triggers?

[frollogaston]

I've done it the other way before, sometimes a team choice rather than my own, and it's ended badly any time the changelog table is actually needed. Startups or just chaotic projects will change requirements and then need data that's only in changelog tables. The changelog tables in the meantime were only barely maintained as an afterthought, lacking FKs of course, and only useful for manual debug if even that.