Databases 2.1/2.2

Strong Entity

an entity that can exist independent of any other entities and has it’s own relationships

Weak Entity

an entity that exists because of another entity and has it’s own relationships

Associative Entity

entity that represents the many to many relationships between other entities

Direct Relationship

a relationship between two entities that does not require on associative table

one-to-one or one-to-many

Composite Key

a key that consists of one or more attributes and in combination uniquely identifies the record

Lookup Table

a type of reference table that provides a list of allowable values to populate an attribute of another table

Reference Table

table that consists of key-value entries

key attribute is primary key and value attribute is what the key represents

Anomalies

inconsistencies that may occur when there are redundencies in data or dependencies between non-key attributes

Partial Dependency (1NF)

occurs when an attribute depends on only part of the primary key

indicates a need for another table

Repeating Groups (1NF)

attributes that hold more than one value within an attribute in a single record

indicates the need for another table

Functional Dependency (2NF)

the primary key determines the value of each non-key attribute within a single record

Transitive Functional Dependency (3NF)

situation where an attribute within a single record depends on another non-key attribute in the same record, which in turn relies on the primary key

does not work, attributes must directly rely on the primary key

Candidate Key

one or more attributes that van uniquely identify a record

primary or alternate key

Alternate Key

a candidate key that uniquely identifies a record but is not selected to be the primary key

Denormalization

rolling back the normalization process to contain some redundant information

increase query performance, optimize operations