[jacques_chester]

> How do hierarchical tables compare to Postgres' hstore?

If I am reading them correctly, it's a storage strategy, not a specific "feature" per se. The closest analogy to hstore is that they provide native support for storing and querying protobuf blobs.

> I think recursive structures like lists and trees are one weakness of the relational model, and haven't found a fully satisfying relational answer to the limitations.

It depends on why you're using trees or graphs.

If it's inherent in the data, then modern SQL has recursive queries that make it much easier than the old methods.

If it's inherent in the model, you will find it harder. You might need to pick a non-standard approach, such as PostgreSQL's inherited tables. I'd think long and hard before saying it's inherent in the model, by the way. Strictly speaking you can represent the same thing as sets of relations or as a graph; it's better to utilise the strengths of the tool in front of you.