26. OPTİONAL VERSUS MANDATORY Neither one is preferable to the other. The proper one to choose depends on the business situation. Mandatory sub-typing is represented by creating a double line from the super-type ( person in the following ER diagram) to the circle. Optional sub-typing is represented by leaving a single line from the super-type to the circle.
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28. AGGREGATİON OF ENTİTY TYPES Consider the relationship between a car and its engine and body. The engine and body are both part of the car. The relationship is represented as follows in an ER diagram.
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30. PARALLEL RELATİONSHİPS A person pays for zero or more insurance policies. An insurance policy is paid for by exactly one person. A person is insured by zero or more insurance policies. An insurance policy insures one or more persons.
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36. TERNARY RELATİONSHİPS Customer Loan Borrow Branch A customer borrows a loan from a branch. Customer Loan Borrow Branch Issue A customer borrows a loan. A loan is issued from a branch.
37. WHAT ARE THE DİFFERENCES? A customer borrows a loan from a branch. A customer borrows a loan. A loan is issued from a branch.
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41. A CASE STUDY A primary school student writes a composition about a picnic: Today is Sep 9, the weather is fine. My classmates, John, Mary and I go to a picnic in Sai Kung. Our teacher is Ms Wong Initial Design: Picnic weather destination date Students Name Teacher Name
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45. E-R DİAGRAM FOR COMPANY DATABASE EMPLOYEE WORKS_FOR MANAGES CONTROLS Startdate DEPARTMENT WORKS_ON PROJECT Hours DEPENDENTS_OF DEPENDENT SUPERVISION supervisee supervisor Fname Minit Lname Name Sex Address Salary Ssn Bdate Number Of Employees Locations Can you translate it back into English? Name Number Name Number Location Relationship Birthdate Sex Name
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