Schemas Integration - Information Systems Reengineering, Integration and Normalization - page 263

Chapter 7
Schemas Integration
Over the last two decades, a number of database systems have come into the market
by using predominant data models: hierarchical, network, relational, object-oriented
(OO), and XML. As the performance of the relational database (RDB) is improved,
it has been accepted by the industry and created the need of converting companies'
hierarchical or network database to RDB and XML. To meet users' requirements,
there is a need to support various data models in a single platform. However, due to
the implied constraints of the various data models, it is difficult for organizations to
support heterogeneous database systems.
The survey results show that coexistence and integration of database systems is
an option to solve the problem. These databases are created and managed by the
various units of the organization for their own localized applications. Thus, the
global view of all the data that is being stored and managed by the organization
is missing. Schema integration is a technique to present such a global view of an
organization's databases. There has been a lot of work done on schema integra-
tion. Batini et al. ( 1992 ) and ￖzsu and Valduriez ( 1991 ) present surveys of work
in this area. But all these techniques concentrate on integrating database schemas
without taking into consideration new database applications. This chapter presents
a practical approach to schema integration to support new database applications by
comparing the existing databases against data requirements of the new applications.
If the existing databases are inadequate to support new applications, then they are
evolved to support them.
RDB system has been dominant in the industry for the last two decades. OO
database application (OODB) is recognized as a postrelational technology that can
improve productivity. Hence, most companies need to enhance their existing RDB
systems to support new OO applications as and when needed. The current trend is to
implement an object-relational database system (ORDB) using a relational engine
with OO features. This chapter proposes a methodology to integrate existing ORDB
systems based on user requirements. We can recover and verify schema semantics
by data mining and store it in metadata. A frame model metadata is used to enforce
constraints for solving semantic conflicts arising from schema integration. The