Materialized view maintenance using version numbers

A data warehouse stores materialized views over data from one or more sources in order to provide fast access to the integrated data, regardless of the availability of the data sources. We define a new compensation algorithm that is used in removing the anomalies, caused by interfering updates at the base relations, of incremental computation for updating the view. Unlike existing methods on view maintenance, our algorithm does not assume that messages from a data source will reach the view maintenance machinery in the same order as they are generated, and we are also able to detect update notification messages that are lost in their transit to the view, which would otherwise cause the view to be updated incorrectly. These are achieved with the use of version numbers that reflect the states of the base relations. Our algorithm also does not require that the system be quiescent before the view can be refreshed