Relational Databases
Key Terms Summary
Attribute
• Describe a data item within an entity
Entity
• an object
• about which data is stored
Primary Key
• uniquely identifies a record in a table
Composite Key
• Consists of more than one attribute
• uniquely identifies an entity occurance/record.
Foreign Key
• a primary key in one entity
• which appears as unknown key field in another entity
• as a link
Relationships
• A link between entities
• established by a foreign key in one entity linking to the primary key in another
• Cardinality shows the maximum number of occurrences
• that can be involved in a relationship
Referential Integrity
• a foreign key
• must correspond to a valid/existing primary key
• in another table
Data duplication
• A non-key attribute
• is stored in two or more separate tables
Data Inconsistency
• an attribute for an entity that has more than one value
Key Terms Summary
Attribute
• Describe a data item within an entity
Entity
• an object
• about which data is stored
Primary Key
• uniquely identifies a record in a table
Composite Key
• Consists of more than one attribute
• uniquely identifies an entity occurance/record.
Foreign Key
• a primary key in one entity
• which appears as unknown key field in another entity
• as a link
Relationships
• A link between entities
• established by a foreign key in one entity linking to the primary key in another
• Cardinality shows the maximum number of occurrences
• that can be involved in a relationship
Referential Integrity
• a foreign key
• must correspond to a valid/existing primary key
• in another table
Data duplication
• A non-key attribute
• is stored in two or more separate tables
Data Inconsistency
• an attribute for an entity that has more than one value
