Clients typically perform complex read-only queries on the views.
The views are refreshed periodically by maintenance transactions, which propagate large batch updates from the base tables. We describe an algorithm called 2VNL that allows warehouse maintenance transactions to run concurrently with readers. By logically maintaining two versions of the database, no locking is required and serializability is guaranteed. On-Line Warehouse View Maintenance for Batch Updates. Doc 97 caching and views in data base systems - Stonebraker, Jhingran et al.