ISYS224 Lecture Notes - Lecture 2: Conceptual Schema, Candidate Key, Unique Key

• School: Macquarie University
• Department: Information Systems
• Course: ISYS224
• Professor: Charanya

Document Summary

Group of objects with same properties, identified by enterprise as having independent existence. Uniquely identifiable association, which includes one occurrence for each participating entity types. Relationship types where same entity type participates more than once in different roles. Given role names to indicate purpose each participating entity type plays in relationship. Property of an entity or a relationship type. Set of allowable values for one or more attributes. Attribute that holds single value for each occurrence of entity type. Attribute that holds multiple values for each occurrence of entity type. Or set of attributes not necessarily in same entity type. Minimal set of attributes that uniquely identifies each occurrence of entity type. Candidate key selected to uniquely identify each occurrence of entity type. Candidate key that consists of two or more attributes. Entity type not existence- dependent on some other entity type isys224 page 1. Entity type existence depdent on some other entity type.