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The Locking Protocol: To manage concurrency related problems we use locking. A lock is mainly a variable that is associated with a data item in the database. A lock can be located by a transaction on a shared resource that it needs to use. When this is completed, the data item is available for the exclusive use for that transaction that is other transactions are locked out of that data item. When the transaction that has locked a data item does not need to use it any longer, it should unlock the data item so that other transactions can use it. If a transaction attempts to lock a data item already locked by some other transaction, it cannot do so and remains for the data item to be unlocked. The parts of DBMS that controls and stores lock information is known as the Lock Manager. The locking mechanism helps us to change a schedule into a serialisable schedule. We had definite what a schedule is, but what serialisable schedule is?
If the deletion violates referential integrity constraint, then three alternatives are available: Default option: - refuse the deletion. It is the job of the DBMS to describ
What are wait-for-graphs?Give the algorithm to construct a wait-for-graph from a given schedule of transactions? How can deadlocks be detected from wait-for-graphs? Ans: The
Representing complex relationship among data A database may contain varieties of data interrelated to each other in numerous ways. A DBMS must have the capability to represent
What is data integrity? Ans: It is the data consisted of in database that is accurate and consistent. (Data integrity means that the data should be valid as per to the give
What does authentication refer? Authentication refers to the task of verifying the uniqueness of a person.
What are the drawbacks of File Oriented System in details?
we need example of 2phase locking
What are the advantages and disadvantages of merging an association into a class? Advantages: i) Less number of tables ii) Faster performance due to the fewer tables
Define Boyce codd normal form A relation schema R is in BCNF with respect to a set F of functional dependencies if, for all functional dependencies in F + of the form.α ->β.
Explain the structure of well formed formulae in relational calculus. Ans: a. An atom is a formula b. If P1 is a formula, after that so are ¬P1 and (P1) c. If P1 and P2 a
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