```json { "classifications": [ { "column": "upc", "role": "identifier", "confidence": 0.99, "reason": "Universal Product Code serving as a unique product identifier with very high cardinality (219k distinct values). Used for lookups and joins, never aggregated." }, { "column": "beer_id", "role": "identifier", "confidence": 0.98, "reason": "Foreign key linking to a beer entity. High cardinality (202k distinct) and used for joins between tables, not for aggregation." }, { "column": "user_id", "role": "identifier", "confidence": 0.97, "reason": "Foreign key referencing a user entity. High cardinality (10k distinct) indicates it's used to identify/join user records, not for aggregation." } ] } ```