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E-R to Relational - Basic • Strong entity • Table with all attributes of that entity • Relationships • Table with primary keys of participating entities • Weak entity • Table with primary key of strong entity • Multi-valued Attribute X • Table with X, primary key of strong entity • Row per value of X • Finally ..
E-R to Relational - Improved • For N-1/1-1 relationships • Move relationship attributes to the N-side entity’s table • Dept id moves to employee. • No need for a table for the relationship relating a weak entity • Remove the “depends” table
Emp-Dept ER Diagram Dept id name Manages department city state color Lic# car Supervises Start date Works for dependent supervisee supervisor reln employee name Supports Owns SSN Name address phones street city
Emp-Dept schema • Employee(SSN, name, street, city, deptid, startdate, supervisor_ssn) • Dept(deptid, name, city, Manager-SSN) • Phone(SSN, phone#) • Dependent(EMP-SSN, Name, relation) • Car(state, license#, color) • CarOwners(owner-SSN, car-state, license#)