What is Electronic Commerce?

							          Extended E-R Model: Basic Symbols

                   Strong Entity Set       Associative Entity Set


                   Weak Entity Set          Attribute


                    Association            Multi-Valued Attribute
                    Relationship Set

                   Identifying                Derived attribute
                   Relationship Set

DB: Extended E-R                       1                    Spring 2003
                   Extended E-R: Relationship
                          Cardinality

                                     Mandatory One


                                     Mandatory Many



                                     Optional One


                                     Optional Many


DB: Extended E-R             2                      Spring 2003
                     Relationship Set: Cardinality

                        Maximum Cardinality for Course         Maximum Cardinality for Offering




                    Course                                                           Offering
                                    (1:1)                              (0:N)
                   Course-NO
                     C-Des
                                                         Has                         Offer-NO
                                                                                    Off-Location
                   Credit-Hour                                                       Off-Time


                                                           Minimum Cardinality for Offering
                        Minimum Cardinality for Course




DB: Extended E-R                                 3                                         Spring 2003
            Graphical Notations for Cardinality
                    EMPLYEE         Works-for       DEPARTMENT   1: One
                              M                 1                M: Many




                   EMPLOYEE                                        : One
                                  Works-for         DEPARTMENT
                                                                   : Many



                                  Works-for
                   EMPLOYEE                     DEPARTMENT Many       One




                   EMPLOYEE                     DEPARTMENT             : One
                                  Works-for
                                                                       : Many


DB: Extended E-R                        4                                   Spring 2003
                    ER Diagram: An Example
            Sends                            SUPPLIER



                                              Supplies


                                                                    CUSTOMER
        SHIPMENT            Includes           ITEM


                    KEY                                              Submits
          Entity          Relationship        Used_in

    Cardinalities
              Mandatory
                  One
           Mandatory Many                    PRODUCT     Requests    ORDER
           Optional One
           Optional Many
DB: Extended E-R                         5                             Spring 2003
                   Weak Entity: An Example
                                                            Last_Name
                    First_Name         Middle_Initial



                                                            Date_of_Birth
    Employee_I        Employee_Name
        D
                                         Dependent_Name




        EMPLOYEE                 Has                    DEPENDENT




DB: Extended E-R                   6                                    Spring 2003
                   Unary Relationship: Examples


                      PERSON                  Marries


                                One-to-one




                     EMPLOYEE                 Manages


                                One-to-many
DB: Extended E-R                   7                    Spring 2003
                   Binary Relationship: Examples

         EMPLOYEE             Assigns       PARKING PLACE

                           One-to-One

      PRODUCT LINE            Contains        PRODUCT

                           One-to-Many

          STUDENT           Registers_for      COURSE

                            Many-to-Many

DB: Extended E-R                 8                      Spring 2003
                   Ternary Relationships: Example

                                          PART



                                      Supplie
               VENDOR                                        WAREHOUSE
                                         s




                      Shipping_mode              Unit_cost



DB: Extended E-R                      9                             Spring 2003
                            Composite Attribute
                                          Addres
                                            s




                   Street_Addres
                                   City            State     Postal_Code
                          s

DB Design Question: Should we model address as a simple or composite attribute?


DB: Extended E-R                      10                               Spring 2003
        Multi-Valued versus Derived Attribute

                                 Employee_Name
                   Employee_ID                   Address




         Years_Employed           EMPLOYEE             Skill




                                 Date_Employed



DB: Extended E-R                   11                          Spring 2003
    Specialization/Generalization Relationships:
    Disjointness and Completeness Constraints

                         PERSON

                                            Overlapping and Partial Coverage
                            IS-A    (O,P)


                   DOCTOR          PATIENT


                                    IS-A    (D,T)
                                                    Disjoint and Total Coverage


                      IN-PATIENT OUT-PATIENT



DB: Extended E-R                            12                           Spring 2003