BUSI 3400 Chapter Notes - Chapter 4: Cardinality, Unique Key

• School: Carleton University
• Department: Business
• Course: BUSI 3400
• Professor: Michael Hine

Document Summary

Erd: depicts the conceptual database as viewed by end user (entities, attributes, relationships) Entity: refers to the entity set and not to a single entity occurrence (i. e. the whole table) Entity instance/occurrence: refers to a row in a table. Required attribute: must have a value, cannot be left empty. Optional attribute: does not require a value, can be left empty. Domain: set of possible values for a given attribute. Identifiers (primary keys): one or more attributes that uniquely identify each entity instance. Composite identifier: primary key composed of more than one attribute. Composite attribute: attribute that can be subdivided to yield additional attributes. Single-valued attribute: attribute that has only a single value. Multivalued attributes: attributes that have many values and require creating (several new attributes, new entity composed on the original values) Derived attribute: attribute whose value is calculated from other attributes. Cardinality: expresses the minimum and maximum number of entity occurrences associated with one occurrence of related entity.