A long, long time ago I came up with a simple something I called Definition Language (DL) and an extension of that I called Data Definition Language (DDL). This was before XML (let alone JSON) became popular, and DL and DDL turned out to be somewhat akin to those.
My intention was a configuration language that would allow a data-dumping tool that knew the structure of the data it was dumping. Debuggers can sometimes do that in context. I wanted a tool that could do that with any file format given some DDL config file. (These days I’d probably just use XML.)