As a non-mathematician I've always conceived of the relations among data as existing in the queries. In a SQL query the "relation" is specified by matching col

As a non-mathematician I've always conceived of the relations among data as existing in the queries. In a SQL query the "relation" is specified by matching columns in the tables containing the data we're looking. Conceptually indexes, etc., are system implementation details. That's certainly not a rigorous definition but helped me keep my head straight about what I was doing.