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

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The application's data can be somewhat out-of-date.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

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

Each transaction may proceed without coordination across the network.
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.

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Distributed Databases
A semijoin is which of the following?

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

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