Amplified E-R Model: Basic Symbols

Presentation Transcript

Expanded E-R Model: Basic Symbols Strong Entity Set Associative Entity Set Weak Entity Set Attribute Association Relationship Set Multi-Valued Attribute Identifying Relationship Set Derived trait

Extended E-R: Relationship Cardinality Mandatory One Mandatory Many Optional One Optional Many

Relationship Set: Cardinality Maximum Cardinality for Offering Maximum Cardinality for Course Has Offering (1:1) (0:N) Course-NO C-Des Credit-Hour Offer-NO Off-Location Off-Time Minimum Cardinality for Offering Minimum Cardinality for Course

EMPLYEE 1: One M: Many DEPARTMENT Works-for 1 M Works-for EMPLOYEE DEPARTMENT Many One Graphical Notations for Cardinality : One EMPLOYEE DEPARTMENT Works-for : Many : One : Many EMPLOYEE DEPARTMENT Works-for

ER Diagram: An Example Sends SUPPLIER Supplies CUSTOMER Includes SHIPMENT ITEM Submits KEY Relationship Used_in Entity Cardinalities Mandatory One Requests PRODUCT ORDER Mandatory Many Optional One Optional Many

DEPENDENT Has EMPLOYEE Weak Entity: An Example Last_Name First_Name Middle_Initial Date_of_Birth Employee_Name Employee_ID Dependent_Name

Unary Relationship: Examples Marries PERSON One-to-one Manages EMPLOYEE One-to-numerous

Binary Relationship: Examples EMPLOYEE Assigns PARKING PLACE One-to-One PRODUCT LINE Contains PRODUCT One-to-Many STUDENT Registers_for COURSE Many-to-Many

PART Supplies VENDOR WAREHOUSE Unit_cost Shipping_mode Ternary Relationships: Example

Address City Postal_Code Street_Address State Composite Attribute DB Design Question: Should we show address as a basic or composite quality?

Employee_Name Employee_ID Address Years_Employed Skill EMPLOYEE Date_Employed Multi-Valued versus Derived Attribute

Specialization/Generalization Relationships: Disjointness and Completeness Constraints PERSON Overlapping and Partial Coverage IS-An (O,P) DOCTOR PATIENT Disjoint and Total Coverage IS-A (D,T) IN-PATIENT OUT-PATIENT