What About Smaller Schemas? Suppose we had started with bor loan.How would we know to split up (decompose)it into borrower and loan? Write a rule "if there were a schema (loan number,amount),then loan_number would be a candidate key" Denote as a functional dependency: loan_number→amount In bor loan,because loan_numberis not a candidate key,the amount of a loan may have to be repeated.This indicates the need to decompose bor loan. Not all decompositions are good.Suppose we decompose employee into employee1=(employee_id,employee_name) employee2=(employee_name,telephone_number,start_date) The next slide shows how we lose information--we cannot reconstruct the original employee relation--and so,this is a lossy decomposition. Database System Concepts-5th Edition,Oct 5,2006 7.6 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 5 7.6 ©Silberschatz, Korth and Sudarshan th Edition, Oct 5, 2006 What About Smaller Schemas? Suppose we had started with bor_loan. How would we know to split up (decompose) it into borrower and loan? Write a rule “if there were a schema (loan_number, amount), then loan_number would be a candidate key” Denote as a functional dependency: loan_number → amount In bor_loan, because loan_number is not a candidate key, the amount of a loan may have to be repeated. This indicates the need to decompose bor_loan. Not all decompositions are good. Suppose we decompose employee into employee1 = (employee_id, employee_name) employee2 = (employee_name, telephone_number, start_date) The next slide shows how we lose information -- we cannot reconstruct the original employee relation -- and so, this is a lossy decomposition