Materialization is an important issue in warehousing, and has also, but to a much less extent, been an issue for data integration mediators in general. An integrated information system in the middle tier integrates data and services from source information systems in the bottom tier. The integration includes both schematic and materialized information of the source information systems, as well as its own integration logic. Flexible materialization strategies to meet different requirements like performance, availability or consistency. The middle tier provides flexible partial materialization of data from the source information systems.
Materialization is partial .
Some data are replicated in the middle tier, while other data are stored only in the bottom tier and are integrated schematically in the middle tier. It also enables information to be pre-integrated before it is actually in use. Schematic integration is preferable when updates at the sources are frequent and maintaining materialized information is too costly. Degree of autonomy of source information systems may also restrict maintaining consistency between materialized and original information. Materialization is adaptive .