FIT2094 Lecture Notes - Lecture 4: Unique Key, Associative Entity, Foreign Key

• School: Monash University
• Department: Information Technology
• Course: FIT2094
• Professor: Mr Lindsay Smith

Document Summary

Each relation has a unique name in the database. Each row is unique - i. e. duplicate tuples are not allowed. The entries are single-valued (atomic) - each cell contains a single entry. Transforming er diagrams into relations (mapping conceptual level to logical level) When the regular entity type contains a composite attribute, only the simple component attributes of the composite attribute are included in the new relation. Compared to composite attributes, simple attributes not only improve data accessibility but also help in maintaining data quality. When the regular entity type contains a multivalued attribute, two new relations are created. The first relation contains all the attributes of the entity except the multivalued attribute itself. The second relation contains two attributes that form the primary key. One of the attributes is the primary key from the first relation, which becomes the foreign key in the second relation and the other is the multivalued attribute.