IMS: The "Dead" Database That Predicted NoSQL. Everyone jokes about IMS being obsolete, but here's the plot twist: its hierarchical structure is nearly identical to modern document databases like MongoDB. IMS organizes data in tree-like structures with parent-child relationships—exactly like JSON documents. While developers are discovering the benefits of document stores for handling complex, nested data structures, mainframes have been doing this since 1966. IMS was XML and JSON before XML and JSON existed.