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Database Design – Lecture 15

Database Design – Lecture 15. Converting a Class Diagram to a Relational Model. Steps to Convert from an Class Diagram to Relational. Simple classes become tables. Identify a unique identifier and make this a primary key. Intersection class becomes a bridge table.

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Database Design – Lecture 15

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  1. Database Design– Lecture 15 Converting a Class Diagram to a Relational Model

  2. Steps to Convert from an Class Diagram to Relational • Simple classes become tables. Identify a unique identifier and make this a primary key. • Intersection class becomes a bridge table. • Remove derived attributes. • For association relationship of 1:M, add the PK of the 1 table as an FK of the M table.

  3. Steps to Convert from an Class Diagram to Relational • For aggregation/composition relationships: • Consider weak/strong entity relationships: • If a weak relationship (aggregation), add the PK of the aggregate as a FK in the ‘part’ (it will not be part of the PK). • If a strong relationship (composition), add the PK of the aggregate as part of a composite primary key of the ‘part’. It will also be a FK.

  4. Steps to Convert from an Class Diagram to Relational • Inheritance relationship: • Create a table for the superclass and a table for each of the subclasses (subtype tables). Unique identifier (primary key) for both tables will be the same, or • Create a table for each subclass (include attributes from superclass in each table), or • Create one table for the entire structure and create a new attribute to denote which type of subclass it is

  5. Steps to Convert from an Class Diagram to Relational • Many-to-many associations: • Create two base tables and a bridge table. The PKs of the base tables will be PK/FKs of the bridge table. • Do normalization.

  6. Steps to Convert from an Class Diagram to Relational • Enrolment Example

  7. Steps to Convert from an Class Diagram to Relational • Enrolment Example Continued

  8. Steps to Convert from an Class Diagram to Relational • Person is a supertype entity of Employee, Dependent and Beneficiary • Create primary key for each table and convert • Tables (option a from rules): PERSON (PERSON_ID (pk), FNAME, LNAME) EMPLOYEE (EMPL_PERSON_ID (pk), SEX, DATEOFBIRTH, ANNUAL_SALARY, ADDRESS) BENEFICIARY (BEN_PERSON_ID (pk)) DEPENDENT (DEP_PERSON_ID (pk), DATEOFBIRTH, RELATIONSHIP)

  9. Steps to Convert from an Class Diagram to Relational • Connectivity between Person supertype and each subtype (Employee, Dependent and Beneficiary is 1:1) • Additional Relationships: • EMPLOYEE:BENEFICIARY is M:N (we already identified an intersection table – EMPLOYEE_BENEFICIARY) • EMPLOYEE:DEPENDENT is 1:M and is a strong/weak relationship (therefore add PK of 1 as a PK,FK of weak)

  10. Steps to Convert from an Class Diagram to Relational • Revised Tables: PERSON (PERSON_ID (pk), FNAME, LNAME) EMPLOYEE (EMPL_PERSON_ID (pk), SEX, DATEOFBIRTH, ANNUAL SALARY, ADDRESS) BENEFICIARY (BEN_PERSON_ID (pk)) DEPENDENT (DEP_PERSON_ID (pk), EMPL_PERSON_ID (pk, fk), DATEOFBIRTH, RELATIONSHIP) EMPLOYEE_BENEFICIARY (EMPL_PERSON_ID (pk, fk), BEN_PERSON_ID (pk, fk), PERCENT)

  11. Steps to Convert from an Class Diagram to Relational • More Tables: PLAN (PLAN_ID (pk), TITLE) CLIENT (CLIENT_ID (pk), ACCOUNT, TITLE, ADDRESS, TELEPHONE, FAX) BENEFIT (BENEFIT_ID (pk), TITLE, PREMIUM_RATE, DESCRIPTION) • Relationships: PLAN: BENEFIT M:N (no intersection class on our OODM) • Revised Tables: PLAN_BENEFIT (PLAN_ID (pk, fk), BENEFIT_ID (pk, fk))

  12. Steps to Convert from an Class Diagram to Relational • Enrolment Bridge Table: ENROLMENT (EMPL_PERSON_ID (pk, fk)), BENEFIT_ID (pk, fk), ENROLMENT_DATE)

  13. Steps to Convert from an OODM to a Rose Model • Final Relationships: CLIENT: EMPLOYEE 1:M PLAN: CLIENT 1:M • Revised Tables: CLIENT (CLIENT_ID (pk), ACCOUNT, TITLE, ADDRESS, TELEPHONE, FAX, PLAN_ID (fk)) EMPLOYEE (EMPL_PERSON_ID (pk), SEX, DATEOFBIRTH, ANNUAL SALARY, ADDRESS, CLIENT_ID (fk))

  14. Object Model vs. Relational Model - Similarities

  15. Object Model vs. Relational Model - Similarities

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