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Questions and Answers
What is the primary key in a table?
What is the primary key in a table?
What is the main characteristic of a relation in 1st normal form?
What is the main characteristic of a relation in 1st normal form?
What is the purpose of normalization?
What is the purpose of normalization?
What is a functional dependency?
What is a functional dependency?
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What is the minimum degree of normalization that is generally considered sufficient?
What is the minimum degree of normalization that is generally considered sufficient?
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What is a candidate key?
What is a candidate key?
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What is the characteristic of a table in 1st normal form?
What is the characteristic of a table in 1st normal form?
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What is the purpose of a primary key?
What is the purpose of a primary key?
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What is the characteristic of a relation?
What is the characteristic of a relation?
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What is the result of normalization?
What is the result of normalization?
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Study Notes
Second Normal Form (2NF)
- In 2NF, every non-key attribute is fully functionally dependent on the entire primary key.
- No partial functional dependencies are allowed.
- Every non-key attribute must be defined by the entire key, not just part of the key.
Third Normal Form (3NF)
- 3NF is 2NF plus no transitive dependencies.
- Transitive dependencies occur when the primary key is a determinant for another attribute, which in turn is a determinant for a third attribute.
- To solve transitive dependencies, non-key determinants with transitive dependencies are moved to a new table, becoming the primary key in the new table and staying as a foreign key in the old table.
Key Fields
- Keys serve two main purposes: primary keys (unique identifiers of a relation) and foreign keys (identifiers that enable a dependent relation to refer to its parent relation).
- Keys can be simple (a single field) or composite (more than one field).
Transforming ER and EER Diagrams into Relations
- Simple attributes in ER diagrams map directly onto the relation.
- Composite attributes are broken down into their simple component attributes.
- Multivalued attributes become a separate relation with a foreign key taken from the superior entity.
Normalization
- First Normal Form (1NF): no multivalued attributes (repeating groups), every attribute value is atomic, and every relation is in 1NF.
- Higher degrees of normalization are possible, but 3NF is generally considered sufficient.
Functional Dependencies and Keys
- Functional dependency: the value of one attribute (the determinant) determines the value of another attribute.
- Candidate key: a unique identifier, one of which will become the primary key.
- Each non-key field is functionally dependent on every candidate key.
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Description
Learn about the principles of Second Normal Form (2NF) and Third Normal Form (3NF) in database normalization, including functional dependencies and transitive dependencies.
