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Failures and Recovery
In practice various things might occur to prevent a transaction from completing. Recovery methods are used to bring database, which does not satisfy consistency needs, into a consistent state. If a transaction finishes normally and commits then all the alters made by the transaction on the database are permanently registered in the database. They should not be lost. But, if a transaction does not finish normally and terminates abnormally then all the changes made by it should be discarded. An abnormal termination of a transaction may be because of various causes, including:
a) User may decide to terminate the transaction issued by him/ her
b) There may be a deadlock in the system
c) There may be a system failure.
The recovery mechanisms must make sure that a consistent state of database can be restored under all circumstances. In case of transaction terminate or deadlock, the system remains in control and can deal with the failure but in case of a system failure the system loses control because the computer itself has failed. Will the results of such type of failure be catastrophic? A database has a vast amount of useful information and any system failure should be recognised on the restart of the system. The DBMS should recover from some such failures.
Can a filed occur in several field groups. Yes. But it leads to redundant data redundancy.
what is specialization?
a) Distinguish between ‘database' and ‘Database Management Systems (DBMS)'. b) List and briefly describe five potential benefits of the database approach compared to conventio
What is assertion? Mention the forms available. An assertion is a predicate expressing a condition that we wish the database always to satisfy. Domain integrity constraints.
In the architecture of a database system which external level used? In the architecture of a database system view external level used.
Define Direct file organization? The direct file organization is employed to enhance the performance in accessing the records than sequential file organization. In direct file
About Attribute inheritance
Strong entity set and weak entity set? Strong entity set and weak entity set: A strong entity set has a primary key. All tuples in the set are distinguishable through that key.
What are temporary tables? Temporary tables exist solely for a particular session or whose data persists for the duration of the transaction.
Define Serializable schedule Serializable schedule: An interleaved schedule of much more than one transaction is known as a serializable schedule, if it is equal to some serial
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