Ask HN: How do you describe organisation wide data structures

I am looking for a way to describe data stored across 50+ systems, each one is managed by a different part of the business. So I was thinking some type of plain text markup language that can be collaboratively edited and results in some type of visualisation of how the data connects to each other.

I was considering building this language myself but it would be good to hear if there are tools that already exist for the purpose.