B ITM 330 Lecture Notes - Lecture 10: Foreign Key, Compound Key, Unique Key

• School: SUNY Albany
• Department: Information Technology Management
• Course: B ITM 330
• Professor: Jakov Crnkovic

Document Summary

Normalizing relations (or breaking them apart into many component relations) Denormalization may significantly increase the complexity of the data structure: the question is one of balance, trading complexity for modification problems, there are situations where denormalized relations are preferred. 1:1 relationships: the maximum cardinality determines how a relationship is represented, 1:1 relationship, the key from one relation is placed in the other as a foreign key. It does not matter which table receives the foreign key. Representing relationships: like a 1:1 relationship, a 1:n relationship is saved by placing the key from one. 1:n relationships table into another as a foreign key: however, in a 1:n the foreign key always goes into the many-side of the relationship, the 1 side is called the parent, the n side is called the child. N:m relationships: to create an n:m relationship, a new table is created.