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Define the concept of aggregation. Give two examples where this concept is useful.
Ans: Aggregation transforms a relationship among the objects into a higher-level object. A new data type known as aggregate is developed which, under specific criteria of "well-definedness," defines aggregation abstractions. Relational databases illustrated as collections of aggregates are structured like a hierarchy of n-ary relations. To keep well-definedness, update operations on such type of databases must keep two invariants. Well-defined relations are different from relations in third normal form. It is displayed that these notions are complementary and both are significant in database design. A top-down method for database design is described that separates decisions concerning aggregate structure from decisions concerning key identification. It is suggested that aggregate types, and other sorts which support real-world abstractions with no introducing Key identification.
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Dependency Preservation It is obvious that the decomposition must be lossless so that we do not lose any information from the relation that is decomposed. Dependency preservati
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An example of a weak entity is Staff because the availabilityID cannot be uniquely identified unless it is used in conjunction with the foreign key known as availabilityID in the A
Complete replication: It implies maintaining of a whole copy of the database at every site. Thus, the reliability & availability and performance for query response are maximized.
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