Database

Database

Distributed Databases has 30 Questions

A distributed database has which of the following advantages over a centralized database?

Software cost
Software complexity
Slow Response
Modular growth
With failure transparency, all of the actions of a transaction are committed or none of them are committed.

True
False
An autonomous homogenous environment is which of the following?

The same DBMS is at each node and each DBMS works independently.
The same DBMS is at each node and a central DBMS coordinates database access.
A different DBMS is at each node and each DBMS works independently.
A different DBMS is at each node and a central DBMS coordinates database access.
Each site (or node) in a distributed system is subject to the same types of failure as in a centralized system.

True
False
A transaction manager is which of the following?

Maintains a log of transactions
Maintains before and after database images
Maintains appropriate concurrency control
All of the above.
Replication may use either synchronous or asynchronous distributed database technologies, although asynchronous technologies are more typical in a replicated environment.

True
False
Location transparency allows for which of the following?

Users to treat the data as if it is at one location
Programmers to treat the data as if it is at one location
Managers to treat the data as if it is at one location
All of the above.
Synchronization for pull replication is less disruptive and occurs only when needed by each site, not when a central master site thinks it is best to update.

True
False
A heterogeneous distributed database is which of the following?

The same DBMS is used at each location and data are not distributed across all nodes.
The same DBMS is used at each location and data are distributed across all nodes.
A different DBMS is used at each location and data are not distributed across all nodes.
A different DBMS is used at each location and data are distributed across all nodes.
With asynchronous technology, if any copy of a data item is updated anywhere on the network, the same update is immediately applied to all other copies or it is aborted.

True
False
Some of the columns of a relation are at different sites is which of the following?

Data Replication
Horizontal Partitioning
Vertical Partitioning
Horizontal and Vertical Partitioning
Databases that are stored on computers at multiple locations and are not interconnected by a network are known as distributed databases.

True
False
Which of the following is true concerning a global transaction?

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 at one local site and the distributed DBMS passes the request to only the local DBMS.
The required data are located in at least one nonlocal site and the distributed DBMS passes the request to only the local DBMS.
An increasingly popular option for data distribution as well as for fault tolerance of any database is to store a separate copy of the database at each of two or more sites.

True
False
A homogenous distributed database is which of the following?

The same DBMS is used at each location and data are not distributed across all nodes.
The same DBMS is used at each location and data are distributed across all nodes.
A different DBMS is used at each location and data are not distributed across all nodes.
A different DBMS is used at each location and data are distributed across all nodes.
Asynchronous technology can result in unsatisfactorily slow response time because the distributed DBMS is spending considerable time checking that an update is accurately and completely propagated across the network.

True
False
Replication should be used when which of the following exist?

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.
The application's data can be somewhat out-of-date.
All of the above.
A distributed unit of work allows various statements within a unit of work to refer to multiple remote DBMS locations.

True
False
Storing a separate copy of the database at multiple locations is which of the following?

Data Replication
Horizontal Partitioning
Vertical Partitioning
Horizontal and Vertical Partitioning
The purpose of timestamping is to avoid the use of locks.

True
False
A distributed database is which of the following?

A single logical database that is spread to multiple locations and is interconnected by a network
A loose collection of file that is spread to multiple locations and is interconnected by a network
A single logical database that is limited to one location.
A loose collection of file that is limited to one location.
Data replication is favored where most process requests are read-only and where the data are relatively static.

True
False
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.
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.
The cost to perform a snapshot refresh may depend on whether the snapshot is simple or complex.

True
False
Which of the following is a disadvantage of replication?

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

True
False
A distributed database can use which of the following strategies?

Totally centralized at one location and accessed by many sites
Partially or totally replicated across sites
Partitioned into segments at different sites
All of the above
In a semijoin, only the joining attribute is sent from one site to another, and then only the required rows are returned.

True
False
Which of the following is not one of the stages in the evolution of distributed DBMS?

Unit of work
Remote unit of work
Distributed unit of Work
Distributed request
The problem of concurrency control is more complex in a distributed database.

True
False