While making good ontology is for sure big and mostly manual effort, it could be interesting to know if there are any techniques / tools, which automate making vendor-specific, intermediate ontologies for ETL process, given, say, rich-enough JSON examples combined with API documentation.
I am aware of Linked Data standards and techniques, but may be there is something in the form of library to make a draft RDFS+ ontology from API call responses?
For example, there are some libraries to guess JSON Schema (I have even written a primitive one myself), so the task does not seem to have problems in theory.
Please, do not consider this question as "software recommendation" one, because I doubt there is any software for this, but at least educated guess at direction I can take with this. I also believe, this is very important for semantic / linked data projects, and I wonder why I can't find any hints and need to ask for help from more experienced here.