Can you explain why streaming joins are necessary. All examples I've seen are bad. For example joining books and author as a stream seems ridiculous, why couldn't the author come up with a better example that is realistic.
Imagine a system monitoring payment transactions. Each transaction stream (e.g., purchase events) could be joined with customer account data (e.g., past purchasing patterns or blacklist flags). Streaming joins enable flagging potentially fraudulent transactions leveraging live context.