Data Warehouse versus Views
Some people have considered data warehouses to be an extension of database views. Earlier we mentioned materialized views as one way of meeting requirements for improved access to data (see Section 5.3 for a discussion of views). Materialized views have been explored for their performance enhancement. Views, however, provide only a subset of the functions and capabilities of data warehouses. Views and data warehouses are alike in that they both have read-only extracts from databases and subject orientation. However, data warehouses are different from views in the following ways:
· Data warehouses exist as persistent storage instead of being materialized on demand.
· Data warehouses are not usually relational, but rather multidimensional. Views of a relational database are relational.
· Data warehouses can be indexed to optimize performance. Views cannot be indexed independent of the underlying databases.
· Data warehouses characteristically provide specific support of functionality; views cannot.
· Data warehouses provide large amounts of integrated and often temporal data, generally more than is contained in one database, whereas views are an extract of a database.