Week 10 UAS Flashcards Preview

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Flashcards in Week 10 UAS Deck (13)
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1
Q

Purpose of Normalization?

A

Normalization is a technique for producing a set of suitable relations that support the data requirements of an enterprise.

Characteristics of a suitable set of relations include:

  • the minimal number of attributes necessary to support the data requirements of the enterprise;
  • attributes with a close logical relationship are found in the same relation;
  • minimal redundancy with each attribute represented only once with the important exception of attributes that form all or part of foreign keys.
2
Q

Types of update anomalies include?

A

Types of update anomalies include:

  1. Insertion
  2. Deletion
  3. Modification
3
Q

Two important properties of decomposition?

A
  1. Lossless-join property enables us to find any instance of the original relation from corresponding instances in the smaller relations.
  2. Dependency preservation property enables us to enforce a constraint on the original relation by enforcing some constraint on each of the smaller relations.
4
Q

UNF (Unnormalized Form)

A

A table that contains one or more repeating groups.

5
Q

1NF (First Normal Form)

A

A relation in which the intersection of each row and column contains one and only one value.

6
Q

2NF (Second Normal Form)

A

A relation that is in 1NF and every non-primary-key attribute is fully functionally dependent on the primary key.

7
Q

3NF (Third Normal Form)

A

A relation that is in 1NF and 2NF and in which no non-primary-key attribute is transitively dependent on the primary key.

8
Q

Functional Dependencies?

A

Functional dependency describes relationship between attributes.
For example, if A and B are attributes of relation R, B is functionally dependent on A, if each value of A in R is associated with exactly one value of B in R.

9
Q

What is Armstrong’s axioms?

A

a set of inference rules, specifies how new functional dependencies can be inferred from given ones.

Armstrong’s axioms are as follows:
(1) Reflexivity
If B is a subset of A, then A → B
(2) Augmentation
If A → B, then A,C → B,C
(3) Transitivity
If A → B and B → C, then A → C
(4) Self-determination A→A
(5) Decomposition
If A → B,C, then A → B and A → C
(6) Union
If A → B and A → C, then A → B,C
(7) Composition
If A → B and C → D then A,C → B,D
10
Q

What is Boyce-Codd Normal Form (BCNF)?

A

A relation is in BCNF if and only if every determinant is a candidate key.

11
Q

Multi-Valued Dependency (MVD)

A

Represents a dependency between attributes (for example, A, B, and C) in a relation, such that for each value of A there is a set of values for B and a set of values for C. However, the set of values for B and C are independent of each other.

12
Q

Fourth Normal Form (4NF)

A

A relation is in 4NF if and only if for every nontrivial multivalued dependency A -» B, A is a candidate key of the relation.

13
Q

Fifth Normal Form (5NF)

A

A relation is in 5NF if and only if for every join dependency in a relation R, each projection includes a candidate key of the original relation.