RDBMS Aptitude Question Answer 2016

RDBMS Aptitude Question Answer 2016.

what is a domain?
the set of allowable value for the attribute is the domain of the attribute.
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what is a tuple?
tuples are the members of a relation.an entity type having attributes can be
represented by set of these attributes called tuple.
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what is a selection?
an operation that selects only some of the tuples in the relation is known as
selection operation.the selection operation yields a horizontal subset of a
given relation.
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what is a join operation?
the join operation allows the combination of two relations to form a new
relation.
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waht are base operations in relational algebra?
union:
the term of the relation as performed by combining the tuples from one
relation with those a second relation to produce a third
relation.duplicate tuples are eliminated.the the relation must be union
compatable.
difference:
the difference of two relations is a third relation having tuples that occur in
the first relation but not in the second relation.
intersection:
the intersection operation selects the common tuples from the two relations.
cartesian product:
the cartesian product of two relations is the concatination of tuples belonging
to the two relations.a new resultant scheme is created consisting of
concatination of all possible combination of tuples.
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what are different dbms facilities?
how many types of facilities are provided by a dbms?
1)the data definition facility or data definition language(DDL)
2)the data manipulation facility or data manipulation language(DML)
3)the data control facility(DCL)
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what is data definition language?
data scheme is specified by a set of definitions which are expressed b a special
language called a DDL.
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what is a data directory or data dictionary?
the result of compilation of DDL statements is a set of tables which are stored
in a special file called data dictionary or data directory.
a data directory is a file that contains metadata i.e data about data.this file
is consulted before actual is read or modified in the database system.
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