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Explain nested relations?
Nested relations
The assumption of INF is a natural one in the bank examples we have considered.
However, not all applications are best modelled by INF relations.
The nested relational model is an extension of the relational model in which domains might be either atomic or relation valued.
We illustrate nested relations by an example from a library. Assume we store for every book the following in formations
Book title
Set of authors
Publishers
Set of keywords
We can see that if we describe a relation for the preceding information, several domains will be monatomic
Authors
Keywords
Complex types
Collection and large object types
Create table books(
...
Keyword-set setoff(varchar(20))
)
Structure types
Creation of values of complex types
Set Difference If R1 and R2 are two union compatible relations or relations then result of R3 =R1- R2 is the relation that have only those tuples that are in R1 but not in R2.
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