The document discusses views and materialized views in data warehousing and decision support systems. It covers three main points:
1) OLAP queries typically involve aggregate queries, so precomputation is essential for fast response times. Materialized views allow precomputing aggregates across multiple dimensions.
2) Warehouses can be thought of as collections of asynchronously replicated tables and periodically maintained views, renewing interest in efficient view maintenance.
3) Materialized views store the results of views in the database for fast access like a cache, but they require maintenance as underlying tables change. Incremental maintenance algorithms are ideal to efficiently update materialized views.