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

The application's data can be somewhat out-of-date.
All of these
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 true concerning a global transaction?

The required data are at one local site and the distributed DBMS passes the request to only the local DBMS.
The required data are at one local site and the distributed DBMS routes requests as necessary.
The required data are located in at least one nonlocal site and the distributed DBMS routes requests as necessary.
The required data are located in at least one nonlocal site and the distributed DBMS passes the request to only the local DBMS.

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Distributed Databases
A distributed database is which of the following?

A loose collection of file that is spread to multiple locations and is interconnected by a network
A loose collection of file that is limited to one location.
A single logical database that is spread to multiple locations and is interconnected by a network
A single logical database that is limited to one location.

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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 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.

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

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

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