I see, that Graph Schema should contain information about:

• directed / not directed
• id type
• nodes attributes / properties
• edges attributes / properties
• weighted / non-weighted

I can suggest to align it as much as possible with GraphAr schema (https://graphar.apache.org/docs/specification/format) to simplify interoperability and integration with other tools. At the moment GraphAr is the only known for me format for graohs in the open lakehouse.