datomic (and partially xtdb /former crux) are OLTPish, and use only such "tuples" , essentially it's up to the user to define what constitutes an entity if at all ("row", "object", "document", whatever) - maybe some entity-id and everything linked to it, but maybe other less-identity-related stuff. Which might feel freeing to extent, but as you said, also expects great responsibility/discipline to cobble the proper properties together.
which could be written as SPARQL queries, I've used these to cut records out of a big graph, I haven't thought seriously if these could be built into a large scale general purpose systems.
The most fun I ever had with Jena was when I used the rules engine for the control plane of a batch processing system which
used stream processing primitives [1]
The Jena folks said my use was completely unsupported, I had looked at the source code and got to understand how the rules engine worked and I knew damn well there was nothing wrong with what I was doing.
I've thought a lot about why production rules have had so little impact on the industry, I mean people really hate drools
That kind of system is particularly strong at handling deep asynchrony, like when a business process at a bank might involve some steps where you might have to wait for a loan office to approve a loan. It's disappointing to me that nobody has tried to use them (so far as I can tell) to deal with the asynchronous comms problems in Javascript though I've yet to get a clear picture in my mind about how to get started on that. (Funny I am getting an idea now so I'm putting a ticket on my personal Kanban board)
[1] I worked later at a place that had a similar engine written in very awkward Scala that allegedly used Either and Optional for error handling but actually dropped errors most of the time; I knew what algebra my engine supported, they argued whether or not something like that had an algebra; my engine got the same answers every time because it tore down the system properly at the end, their engine gave different answers every time but they didn't seem to care
