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Data Modeling Supplement

Data Modeling Supplement. Six Blind Men and the Elephant. Entity. Relationship. Attribute. Multivalued Attribute. Associative Entity. Basic ERD Symbology. PRODUCTS. CUSTOMERS. are purchased by. SUPPLIERS. PRODUCTS. supply. ORDERS. PRODUCTS. contain. ORDERS. CUSTOMERS.

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Data Modeling Supplement

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  1. Data Modeling Supplement

  2. Six Blind Men and the Elephant

  3. Entity Relationship Attribute Multivalued Attribute Associative Entity Basic ERD Symbology

  4. PRODUCTS CUSTOMERS are purchased by SUPPLIERS PRODUCTS supply ORDERS PRODUCTS contain ORDERS CUSTOMERS are placed by EMPLOYEES OFFICES are assigned to PRODUCTS STORES are sold in Typical Business Relationships

  5. (a) Each EMPLOYEE must be assigned to one and only one OFFICE. Each OFFICE may be assigned to one and only one EMPLOYEE. EMPLOYEE OFFICE assigned to assigned to (b) Each EMPLOYEE must be assigned to one and only one DEPARTMENT. Each DEPARTMENT may be in charge of zero or more EMPLOYEEs. EMPLOYEE DEPARTMENT assigned to in charge of (c) Each STUDENT may be registered for zero, one, or many COURSEs. Each COURSE may be taken by zero, one, or many STUDENTs. STUDENT COURSE registered for taken by Relationship Complexities

  6. PERSON married to COURSE EMPLOYEE is a prerequisite for managed by has as a prerequisite manage Each PERSON may be married to one and only one PERSON. Each COURSE may have zero, one, or many prerequisite COURSEs. Each COURSE may be a prerequisite for zero, one, or many COURSEs. Each EMPLOYEE must be managed by one and only one EMPLOYEE. Each EMPLOYEE may manage zero, one, or many EMPLOYEEs. Unary Relationship

  7. EMPLOYEE OFFICE assigned to assigned to COURSE STUDENT registered for taken by CUSTOMER ORDER place placed by Each EMPLOYEE must be assigned to one and only one OFFICE. Each OFFICE may be assigned to one and only one EMPLOYEE. Each STUDENT may be registered for zero, one, or many COURSEs. Each COURSE may be taken by for zero, one, or many STUDENTs. Each CUSTOMER may place zero, one, or many ORDERs. Each ORDER must be placed by one and only one CUSTOMER. Binary Relationship

  8. STUDENT ADVISOR MAJOR Each STUDENT must have declared one or more MAJORs and be assigned to one or more ADVISORs. Each ADVISOR must be assigned to one or more STUDENTs and be responsible for one or more MAJORS. Each MAJOR must be declared by one or more STUDENTs and be assigned to one or more ADVISORs. Ternary Relationship

  9. (a) PASSENGER SCHEDULED FLIGHTS make reservation reserved by (b) PASSENGER RESERVATION SCHEDULED FLIGHTS Associative Entity

  10. Each… entity1 relationship entity2 must be or may be { } one or more or one and only one { } Each… CUSTOMER may be placing one or more ORDERS. ORDER must be placed by one and only one CUSTOMER Reading Relationships

  11. Characteristic Explanation Pictorial  A good data model should be an accurate graphical depiction of the entities and their relationships Rigorous and Specific  A good data model should be specific with regard to the identification of all entities and their relationships and rigorous in the identification and specification of the attributes associated with each entity. Top-down Decomposable  A good data model should be decomposable in the sense that the level of detail for each entity and its associated attributes can be investigated at various levels of detail or aggregation. Provide Focus  A good data model should be focused on the data associated with a single system and contained within a single system boundary. Minimally Redundant  A good data model will display minimal redundancy with regard to repeated entity types, data redundancy, and many-to-many relationships. Transparent  The actual data and the physical structure of the database should be discernable from looking at the graphical data model. Easily Navigated  A good data model should be laid out in an organized fashion to allow for the relationships among the entities to be easily followed. Predicts the Final System  A good data model should be an accurate prediction of the physical implementation of the system. Characteristics of a Good Data Model

  12. Question Category Description Determine System Entities Find out what types of people, business units, things, places, events, materials, or other organizations are associated with, or interact with, the system and about which data must be maintained. Identify Entity Attributes Identify the characteristics by which each entity is associated or identified with. Determine Entity Keys Identify the most appropriate characteristic for each entity that uniquely distinguishes an instance of that entity from all other instances of the same entity. Determine Relationships and Degrees Identify the various events, transactions, or other business activities that infer an association between entities. Determine Cardinalities and Optionalities Identify the circumstances under which each of the relationships can occur. This requires an investigation into the various business rules under which the organization operates and the constraints imposed on the events which occur within the business environment. Identifying Entities and Relationships

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