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11. 11  Includes all modeling concepts of basic ER  Additional concepts: subclasses/superclasses, specialization/generalization, categories, attribute inheritance  The resulting model is called the enhanced- ER or Extended ER (E2R or EER) model  It is used to model applications more completely and accurately if needed  It includes some object-oriented concepts, such as inheritance

12. 12  An entity type may have additional meaningful subgroupings of its entities  Example: EMPLOYEE may be further grouped into SECRETARY, ENGINEER, MANAGER, TECHNICIAN, SALARIED_EMPLOYEE, HOURLY_EMPLOYEE,… ◦ Each of these groupings is a subset of EMPLOYEE entities ◦ Each is called a subclass of EMPLOYEE ◦ EMPLOYEE is the superclass for each of these subclasses  These are called superclass/subclass relationships.  Example: EMPLOYEE/SECRETARY, EMPLOYEE/TECHNICIAN

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14. 14  Generalization is a bottom-up approach in which two lower level entities combine to form a higher level entity.  In generalization, the higher level entity can also combine with other lower level entity to make further higher level entity.

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16. 16  Specialization is opposite to Generalization.  It is a top-down approach in which one higher level entity can be broken down into two lower level entity.  In specialization, some higher level entities may not have lower-level entity sets at all.

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20. 20  Aggregation is a process when relation between two entity is treated as a single entity.

21. 21 Entity Entity Name

22. 22  Each entity type becomes a table  Each single-valued attribute becomes a column  Derived attributes are ignored  Composite attributes are represented by components  Multi-valued attributes are represented by a separate table  The key attribute of the entiry type becomes the primary key of the table

23. 23  Here address is a composite attribute  Years of service is a derived attribute (can be calculated from date of joining and current date)  Skill set is a multi-valued attribute  The relational Schema Employee (E#, Name, Door_No, Street, City, Pincode, Date_Of_Joining) Emp_Skillset( E#, Skillset)

24. 24 Employee Table EmpCode PK EmpName DateofJoining SkillSet EmpCode FK Skills

25. 25  Weak entity types are converted into a table of their own, with the primary key of the strong entity acting as a foreign key in the table  This foreign key along with the key of the weak entity form the composite primary key of this table  The Relational Schema Employee (E#,…….) Dependant (Employee, Dependant_ID, Name, Address)

26. 26 Employee Table EmpCode PK EmpName DateofJoining SkillSet Dependent EmpCode PK /FK Dependent_ID PK Name Address

27. 27  The way relationships are represented depends on the cardinality and the degree of the relationship  The possible cardinalities are: 1:1, 1:M, N:M  The degrees are: Unary Binary Ternary …

28. 28  Case 1: Combination of participation types The primary key of the partial participant will become the foreign key of the total participant Employee( E#, Name,…) Department (Dept#, Name…,MgrE#) department Employee Manages 11 partia l Total

29. 29 Employee Table EmpCode PK EmpName DateofJoining SkillSet Department DeptCode PK DeptName Location MgrEmpCode FK

30. 30  Case 2: Uniform participation types The primary key of either of the participants can become a foreign key in the other Employee (E#,name…) Chair( item#, model, location, used_by) (or) Employee ( E#, Name….Sits_on) Chair (item#,….) EmployeeCHAIR Sits_on

31. 31 Employee Table EmpCode PK EmpName DateofJoining SkillSet Chair ItemNo PK Model Location Used_By FK Chair ItemNo PK Model Location Employee Table EmpCode PK EmpName DateofJoining SkillSet Sits_On FK

32. 32 The primary key of the relation on the “1” side of the relationship becomes a foreign key in the relation on the “N” side Teacher (ID, Name, Telephone,...) Subject (Code, Name,..., Teacher) Teacher teaches Subject 1N

33. 33 Teacher TeacherID PK Name Telephone Cabin Subject SubCode PK SubName Duration TeacherID FK

34. 34  A new table is created to represent the relationship  Contains two foreign keys - one from each of the participants in the relationship  The primary key of the new table is the combination of the two foreign keys Student (Sid#,Title…) Course(C#,CName,…) Enrolls (Sid#, C#) Student Enrolls Course M N

35. 35 Course CourseID PK Coursename Enrolls StudentCode PK / FK CourseID PK / FK DOIssue Status Student StudentID PK StudentName DOB Address

36. 36 Self referencing 1:N Employee( E#, Name,…,Manager) The primary key field itself will become foreign key in the same table Same as unary 1:1

37. 37 Employee Table EmpCode PK EmpName DateofJoining SkillSet Manager FK

38. 38  There will be two resulting tables. One to represent the entity and another to represent the M:N relationship as follows Employee( E#, Name,…) Guaranty( Guarantor, beneficiary) Employee Guarantor_of M N

39. 39 Employee Table EmpCode PK EmpName DateofJoining SkillSet Guaranty Guarantor PK/FK Beneficiary PK /FK

40. 40  Represented by a new table  The new table contains three foreign keys - one from each of the participating Entities  The primary key of the new table is the combination of all three foreign keys  Prescription (Doctor#, Patient #, Medicine_Name)

41. 41 Doctor DocID PK Title Prescription DocID PK / FK PatCode PK / FK MedName PK/ FK NextVisit Medicine MedName PK ExpDate Patient PatCode PK PatName DOB Address

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43. 43 The relational schema for the ER Diagram is given : Company( CompanyID, name, address ) Staff( StaffID, dob, address, WifeID) Child( ChildID, name, StaffID ) Wife ( WifeID, name ) Phone(PhoneID, phoneNumber, StaffID) Task ( TaskID, description) Work(WorkID, CompanyID, StaffID, since ) Perform(PerformID, StaffID, TaskID )