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 .
The collection of materialized data will vary depending on the current use of the system. A particular set of data may be materialized in the middle tier for a period in which they are of high current interest, while they are excluded from the middle tier during periods of low current interest. Factors that may influence materialization include performance, current data access patterns, consistence levels, autonomy of source information systems, connectivity between source information systems and the integrated information system, and so on. This includes, among others, relating data at different source information systems, supplying domain-specific information, applying particular consistency strategies, and so on. During the treatment of one patient, information from different sources need to be gathered.