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1、2022/10/15Database Principles & Programming1E-R diagramsa entityrepresenting as a rectanglea single-valued attributerepresenting as a ovalattached by a straight line to the entity.a composite attributeis also in an oval attached directly to the entitythe simple attributes that make up the composite

2、are attached to the composite oval.a multi-valued attributeis attached by a double line to the entity it describes.2022/10/15Database Principles & Programming2Transforming Entities and Attributes to RelationsTransformation Rule 1An entity is mapped to a single table. The single-valued attributes of

3、the Entity are mapped to columns (composite attributes are mapped to multiple simple columns).Transformation Rule 2A multi-valued attribute must be mapped to its own table.2022/10/15Database Principles & Programming3Employeeseidemp_addressstaddresscitystatehobbiesEmployees(eid, staddress, city, stat

4、e, zipcode)Hobbies( hobby, eid )Rule 1Rule 22022/10/15Database Principles & Programming4Relationships among EntitiesInstructorsCourse_SectionsteachesEmployeesProjectsworks_onpercentEmployeesmanagesmanager_ofreports_to2022/10/15Database Principles & Programming5Relationships among EntitiesInstructors

5、Course_Sectionsteaches(0, N)(1, 1)Cardinality of Entity Participation in a RelationshipM a n y _ t o _ O n e1N2022/10/15Database Principles & Programming6Relationships among Entities(1, N)(0, N)Cardinality of Entity Participation in a RelationshipEmployeesProjectsworks_onpercentNNM a n y _ t o _ M a

6、 n y2022/10/15Database Principles & Programming7Relationships among Entities(0, N)(0, 1)Employeesmanagesmanager_ofreports_to2022/10/15Database Principles & Programming8Transforming Binary Relationships to RelationsTransformation Rule 3. N-N Relationshipsthe relationship is mapped to a representative

7、 table T in the related relational database design.EmployeesProjectsworks_onpercentNNworks_on ( eid, prid, percent )2022/10/15Database Principles & Programming9Transforming Binary Relationships to RelationsTransformation Rule 4. N-1 Relationshipsrepresent with foreign key in entity with single value

8、d participation (the Many side).InstructorsCourse_Sectionsteaches1Ncourse_sections ( sec_id, ins_id, )Foreign key2022/10/15Database Principles & Programming10Transforming Binary Relationships to RelationsTransformation Rule 5&6. 1-1 RelationshipsOptional on one sideRepresent as two tables, foreign k

9、ey column in one with mandatory participation: column defined to be NOT NULL.Mandatory on both sidesnever can break apart. Its appropriate to think of this as two entities in a single table.2022/10/15Database Principles & Programming11Transforming Relationships in Single EntityTransformation Rule 7&8Employees ( emp_id, mgr_id, )foreign key, manager of emp_id(0, N)(0, 1)Employeesmanagesmanager_ofreports_to2022/10/15Database Principles & Programming12Transforming Rel