[BurningFrog]

Seems fine to me, provided some sanity constraints, like having read-only access, and some guarantee that the fields you're interested in will not be removed/changed.

I've worked on systems that use a SQL DB as a communication layer. A main advantage is that every language comes with good SQL read/write libraries, so things just work right away.

[klysm]

A SQL database is an excellent integration tool that I think is very underutilized. You get strong semantics around transaction isolation, and can easily bake in permissions. Language support is nearly universal and you can avoid a ton of API decisions that are already made for you.