MGCR 331 Lecture Notes - Lecture 12: Data Integrity, Unique Key, Foreign Key
Document Summary
Entities (entity classes: person, place, object, event or concept about which data is maintained, ex: student, course, patient, doctor. Attribute (information or field: named property of an entity, ex: student id, course name, credits, medical school. Relationships: ties between different entities, ex: student takes a class, notation. Primary key: attributes that can uniquely identify a given entity (or relationship) for instance. Foreign key: attributes that can uniquely identify a given entity (or relationship) instance in another entity. Candidate key: attribute (or combination of attributes) that uniquely identifies each instance of an entity type. Identifier (primary key: a candidate key that has been selected as the unique identifying characteristic for an entity type. Identifier attributes: notation: underline the attribute that is the primary key, no notation for candidate keys. Composite attributes: an attribute that can be broken down into more than one attributes known as meaningful component parts, notation: compositeattributename (attribute 1, attribute 2, attribute 3)
