I'm thinking about writing a new programming language: an ANSI SQL compatible language that natively interoperates with real code (Python, Typescript, Rust, etc.) and lets you manage your data model, views, etc. as 1st class programming constructs.

Sounds like an ontologically daunting task! Perhaps there is an existing database suitable for data modeling, perhaps dealing in graphs and a DSL that is SQL-like?

Attempting to ask in a non pretentious way: which aspect feels (ontologically) difficult?