Distributed Databases
A semijoin is which of the following?

Only the joining attributes are sent from one site to another and then all of the rows are returned.
Only the joining attributes are sent from one site to another and then only the required rows are returned.
All of the attributes are sent from one site to another and then only the required rows are returned.
All of the attributes are sent from one site to another and then only the required rows are returned.

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Distributed Databases
Replication should be used when which of the following exist?

When transmission speeds and capacity in a network prohibit frequent refreshing of large tables.
All of these
When using many nodes with different operating systems and DBMSs and database designs.
The application's data can be somewhat out-of-date.

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Distributed Databases
An autonomous homogenous environment is which of the following?

A different DBMS is at each node and a central DBMS coordinates database access.
The same DBMS is at each node and a central DBMS coordinates database access.
The same DBMS is at each node and each DBMS works independently.
A different DBMS is at each node and each DBMS works independently.

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Distributed Databases
Which of the following is a disadvantage of replication?

If the database fails at one site, a copy can be located at another site.
Reduced network traffic
Each site must have the same storage capacity.
Each transaction may proceed without coordination across the network.

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