The article lays out a classification for how transactional (OLTP), analytical (OLAP), hybrid (HTAP), and LTAP systems relate across systems, workloads, storage tiers, data visibility, and durable copies. It defines five categories—single tier, internal tiering, hybrid (with freshness-by-composition and freshness-by-catchup), materializing, and shared tiering—and explains their trade-offs and example technologies.