
548 Appendix
Figure A.5 illustrates our framework, which can be regarded as a model for data management
systems. This framework consists of three layers. One can think of the component technologies,
which we will also refer to as components, belonging to a particular layer to be more or less built on
the technologies provided by the lower layer. Layer I is the Database Technology and Distribution
Layer. This layer consists of database systems and distributed database systems technologies. Layer
II is the Interoperability and Migration Layer. This layer consists of technologies such as hetero-
geneous database integration, client–server databa ...