ACC 340 Lecture Notes - Lecture 9: Unique Key, Foreign Key, Candidate Key
3 main relationship types in the REA ontology:
Define relationship
duality: Event-Event
stockflow: Event-resource
participation: Event-agent
Database components included in REA modeling:
Entities
Relationships
Attributes
Cardinatlities
Simple attributes
Cannot be broken down further
ex. Social security numbers
Composite attributes
Can be broken down into simple attributes
ex. address (into street, city, state, etc.)
Name for rows in the tables
Row extension or tuples
Name for columns in the tables
Table intension or schema
Principles of relational databases:
Entity integrity -
A primary key in a table must not contain a null value. This guarantees the uniqueness of entities and
enables proper referencing of primary key values by foreign key values.
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
3 main relationship types in the rea ontology: Define relationship duality: event-event stockflow: event-resource participation: event-agent. Can be broken down into simple attributes ex. address (into street, city, state, etc. ) A primary key in a table must not contain a null value. This guarantees the uniqueness of entities and enables proper referencing of primary key values by foreign key values. A value for a foreign key in a table must either be null (blank) or match exactly a value for the primary key in the table from which it was posted. Only one instance of a pairing of a candidate key attribute value with another attribute value per cell. (attributes must go with primary key) Formed from a many-to-many relationship, the combination of the two primary keys is called a concatenated primary key. Primary key of the many table should be posted into the one table.
