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Explain weak and strong entity type ?
Weak and Strong entity type: An entity set which does not have a primary key is referred to as a weak entity set. The existence of a weak entity set depends on the existence of a strong entity set; it must associate to the strong set via a on-to-many relationship set. A discriminator of a weak entity set is the set of attributes that distinguishes between all the entities of a weak entity set. The primary key of a weak entity set is formed by the primary key of the strong entity set on that the weak entity set is existence depends, plus the weak entity set's discriminator.
deffine class&object
Example - ALTER TABLE emp MODIFY (empno NUMBER (7));
If R1 and R2 are two union compatible relations or functions, then the result of R3 = R1 ∩R2 is the relation that contains all tuples that are in both the relations In other words,
vertical fragmentation
Rules Of Data Normalisation Let us now summarise Normalisation with the help of various clean rules. The following are the necessary rules for the Normalisation process: 1.
There are two major types of fragmentation: Horizontal& Vertical. Horizontal fragments, as the name suggests are subsets of tuples and vertical fragments are subsets of attributes
About Attribute inheritance
Discuss the term- Design Optimization We have seen various ways of representing the objects.The fundamental design model uses analysis model as the framework for implementati
What is the meaning of Recovery? In deferred update methods, if a transaction fails before arriving its commit point, it will not have altered the database in any way, so UNDO
Entity types that do not have any key attribute, and therefore cannot be identified independently, are known as weak entity types. A weak entity can be recognized uniquely only by
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