schema for tables

I previously proposed a schema for a relational database to hold the Physics Derivation Graph content but ended up using nested dictionaries and lists in v7.

One of the tasks associated with using the nest dictionaries was a desire to convert the content to a table design. I came up with two potential schemas for derivations but wasn't comfortable with either of them. In this post I outline a schema for tables that should work. The consequence is improved JSON-to-tables in v7 as well as enabling the transition from v7 to v8.

Columns per table:

• "step ID", "inference rule", "derivation name", "linear index"
• "step ID", "input local ID", "input index"
• "step ID", "output local ID", "output index"
• "step ID", "feed local ID", "feed index"
• "local ID", "global ID"
• "global ID", "expr latex", "AST as JSON"
• "symbol ID", "symbol latex"
• "symbol ID", "reference URL"
• "operator name", "operator latex"
• "operator name", "reference URL"

What's not clear to me is how to store an AST. The AST relates the use of symbols and operators in a tree structure. 

https://www.reddit.com/r/AskProgramming/comments/7go3b2/sql_schemas_or_nosql_alternatives_for_storing/

--> store AST as JSON