What does "Query Federation" mean?

Question

I ran across this term and can't find a good simple definition describing what this means. Please help.

Answer 1

A federated database contains a mixture of tables and references to tables in other systems. For example, a DB2 database may contain DB2 tables, and "nicknames" for Informix tables. Then you can use them together, e.g. you can perform a join or union between tables on different systems. The query compiler uses information about the Informix system and about the local tables to run the query efficiently.

Feel free to email me (see my profile) if you have more questions on this topic - I work with federated databases a lot.