Flashcards in Week 10 UAS Deck (13):
Purpose of Normalization?
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.
Types of update anomalies include?
Types of update anomalies include:
Two important properties of decomposition?
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.
UNF (Unnormalized Form)
A table that contains one or more repeating groups.
1NF (First Normal Form)
A relation in which the intersection of each row and column contains one and only one value.
2NF (Second Normal Form)
A relation that is in 1NF and every non-primary-key attribute is fully functionally dependent on the primary key.
3NF (Third Normal Form)
A relation that is in 1NF and 2NF and in which no non-primary-key attribute is transitively dependent on the primary key.
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.
What is Armstrong's axioms?
a set of inference rules, specifies how new functional dependencies can be inferred from given ones.
Armstrong’s axioms are as follows:
If B is a subset of A, then A → B
If A → B, then A,C → B,C
If A → B and B → C, then A → C
(4) Self-determination A→A
If A → B,C, then A → B and A → C
If A → B and A → C, then A → B,C
If A → B and C → D then A,C → B,D
What is Boyce-Codd Normal Form (BCNF)?
A relation is in BCNF if and only if every determinant is a candidate key.
Multi-Valued Dependency (MVD)
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.
Fourth Normal Form (4NF)
A relation is in 4NF if and only if for every nontrivial multivalued dependency A ->> B, A is a candidate key of the relation.