BUSI 3400 Lecture Notes - Lecture 4: 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. Must have a value, cannot be left empty. Does not require a value, can be left empty. Domain set of possible values for a given attribute. One or more attributes that uniquely identify each entity instance. Primary key composed of more than one 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) Attribute whose value is calculated from other attributes. Expresses the minimum and maximum number of entity occurrences associated. Pk of the related entity does not contain a pk component of.