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Strict 2PL:Though, this basic 2PL suffers from the trouble that it can result into loss of isolation / atomic property of transaction as theoretically speaking once a lock is released on a data item it can be changed by another transaction before the first transaction aborts or commits.
To leave such a situation we use strict two phase locking. The strict 2PL is graphically depicted in Figure. Though, the basic drawbacks of strict 2PL are that it restricts concurrency as it locks the item afar the time it is required by a transaction.
Figure: Strict Two Phase Locking
Does the two phase locking solve all the problems of concurrent transactions? No, the strict 2PL answers the problem of concurrency and atomicity, though it introduces another problem.
How are tables stored on Disk? We realise that every record of a table can have different amounts of data. This is due to in some records; some attribute values may be "zero".
A constraint named less_than_20 was defined on the field date_of_birth of table student. Delete this constraint. ALTER TABLE student DROP CONSTRAINT less_than_20;
What is a recursive relationship? Give an example not used in the text. A recursive relationship is a relationship among an entity and itself. For example, given the entity PER
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Mappings between Levels and Data Independence The 3 levels of abstraction in the database do not exist separately of each other. There must be some correspondence, or mapping
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Question: AirwaysCentre, an international airline booking company currently uses a relational database system for their operations, which includes the following relations: P
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