You might try pages 8-16 of this presentation: https://www.categoricaldata.net/cql/lambdaconf.pdf . The examples are relational to relational and simplistic but they do illustrate running the same transformation both forward and backward, as well as show the "unit" of such a "monad". We implemented everything in public software, so hopefully the software is even better than my word! As for loading SQL to RDF specifically, I'd be happy to share that technique, but it isn't public yet- please ping me at [email protected].