Database [3i Infotech Placement]: Sample Questions 235 - 236 of 294

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Question 235

Database
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Write in Short

Short Answer▾

How is the data structure of System R different from the relational structure?

Explanation

Unlike Relational systems in System R

  • Domains are not supported
  • Enforcement of candidate key uniqueness is optional
  • Enforcement of entity integrity is optional
  • Referential integrity is not enforced

Question 236

Database
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Describe in Detail

Essay▾

What is cold backup and hot backup (in case of Oracle) ?

Explanation

Cold Backup

  • Physical backup with all the files of a database copied without any change- avoids the risk of copying data
  • Image copy can be easily moved to another system having the same operating system.
  • Can be done to another disk on the server where the database resides.
  • Possible only when the database is down- not available to users to access.
  • An image copy of the database at a point in time.
  • Cannot be interrupted by a virus or intruder, and are immune to power surges and electrical interruptions.
  • Cold data backups prevent accidental overwrites or deletions.

Hot Backup

  • Physical backup with the risk that during the hot backup the database is totally open and available to its users.
  • Dynamic or online backup- performed on data while the database is actively online and accessible to users.
  • Standard way of doing most database backups.
  • Can provide a convenient solution in multiuser systems because they do not require downtime, as cold backups do.
  • If a data loss failure does occur, the lost database files can be restored using the hot backup and the online and offline redo logs created since the backup was done.
  • Database is restored to the most consistent state without any loss of committed transactions.

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