Overview/Review of DB Logical Design ER Model to Relational Model Mapping

Transforming ER into RDB attr relationships entities table ERRDB

Transforming ER into RDB (2) Make a relation for each entity  Unique identifier of entity becomes key of relation  Attributes of entity becomes attributes of relation For each 1 - M relationship:  Take the primary key of the 1-side entity and place it as a foreign key in the M-side entity relation

Transforming ER into RDB (3) relationships can be mapped similarly when compared to 1 - M’s  Where do you house the foreign key? Make a relation for each M - M relationship  Attributes of relation Attributes of relationship + key of each entity  Primary key of relation Unique identifier of each entity {+ attribute of relationship}

Transforming ER into RDB (4) Example: Staff (StaffNo, Address, …) Branch (BranchNo, TelNo, …) Property (PropNo, Rent, …, StaffNo, BranchNo) IsAllocated (StaffNo, BranchNo, Percent) Staff IsAllocated Branch Oversees Property Has StaffNo PropNo BranchNo M M 1M M 1 Rent Address Percent TelNo Note: Underline attributes are PKs and italics are FKs; an attribute can be both PK and FK

Transforming ER into RDB (5) Sometimes a 1 - M relationship should be mapped into a separate relation E.g., Employee (Emp#, …) Car (Car#, …) IsAssigned (Emp#, …., Car#) Emp# Car# IsAssigned Employee Car M1

ER to Relational: Exercise Owns Car MarriedTo Accident Logs License# VIN M M 1M 1 Damage $ Person SS# model Spouse SS# 1 Age