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Explain the Concept of Two-phase Locking
It concerns the positions of locking and unlocking operations in each transaction. In this protocol every transaction issue lock and unlock requests in two phases.
Growing Phase: In this phase a transaction might acquire locks but may not release any lock. Here the of locks rises from zero to the maximum for the transaction.
Shrinking Phase: In this phase a transaction might release locks but may not obtain any new locks. Here the number of locks reduces from maximum to zero.
The major concept of this protocol is that, all the locks are first obtained before any of the locks released. No new locks can be granted later than the releasing of any lock.
Creating a view: A query can be embedded within the CREATE VIEW STATEMENT A query can have complex select statements containing join, groups and sub- queries A quer
What is Multivalued Attribute? Multivalued Attribute - Multivalued attribute might have more than one value for an entity. For instance, PreviousDegrees of a STUDENT.
Write short note on Events Events consist of inputs, interrupts, decisions and actions performed by any external device or users. Every event always has a sender and receiver.
What is persistency? Persistency ensures which data is stored and that after the object is no longer available (program stops running) the data will be available to other users
DISADVANTAGES OF RDBMS
Consider employee (e_no, e_name, e_salary, d_code), dept (d_code, d_name) and dependent (depndt_name, e_no, relation). Show the names of employees in purchase and accounts departm
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Write short notes on tuple relational calculus. The tuple relational calculation is anon procedural query language. It defines the desired information without giving a particul
Differance between Open addressing and chaining for collision resolution ? In open addressing , proceeding from the occupied position specified by hash address the program che
Explain Candidate Key and Super Key A super key is a set of one or more than attributes that, taken collectively, permits us to identify uniquely a tuple in the relation. Wher
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