3i Infotech Papers: Sample Questions 420  421 of 1245
Examrace Placement Series prepares you for the toughest placement exams to top companies.
Question number: 420
Describe in Detail
In RDBMS, what is the efficient data structure used in the internal storage representation.
Explanation
In RDBMS, B + tree structure is the efficient data structure used in the internal storage representation.
B + tree:

A “B + tree” is an narray tree with a node, which consists of a large number of children per node.

Root is a leaf or a node containing more than two children consists of a root internal nodes and leaves.

Same as a B tree, difference is that B + tree is an additional level added at bottom with leaves.

Primary value of the B + tree is in storing and maintaining the data.

Provides an efficient housing data structure format, which makes them simple in accessing and storing Useful as database system index.
Question number: 421
Describe in Detail
What are Armstrong rules? How do we say that they are complete and/or sound
Explanation

Armstrong’s Axioms is a set of rules.

Provides a simple technique for reasoning about functional dependencies.

Used to infer all the functional dependencies on a relational database.
The wellknown inference rules for FD

Reflexivity:

If A is a set of attributes and B is a subset of A, then A holds B.



Augmentation

If A hold B and C is a set of attributes, then AC holds BC.


It means that attribute in dependencies does not change the basic dependencies.


Transitivity

If A holds B and B holds C, then A holds C.

If then

A hold means that A functionally determines B.


Union

If A holds B and A holds C, then A holds BC.

If and


Pseudo Transitivity

If A holds B and BC holds D, then AC holds D.

If


First three are known as Amstrong Rules.

They are sound because it is enough if a set of FDs satisfy these three. They are called complete because using these three rules we can generate the rest all inference rules