Subject: Distributed Database

Topic: Heterogeneous Database

Difficulty: High

There are several issues for query processing in a heterogenous database.

• Schema translation

Write a wrapper for each data source to translate data to a global schema. Wrappers must also translate updates on global schema to update on local schema • Limited query capabilities

Some data sources allow only restricted forms of selection e.g. web forms, flat file data sources.

Quires have to be broken up and processed partly at the source and partly at a different site.

• Removal of duplicate information when sites have overlapping information

Decide which sites to execute query.

• Global query optimization