Entity Relationship Diagrams Used for conceptual data modeling part of database design Represents the data that is important the structure of the data the relationships between different pieces of data Does NOT show process roles users etc Basic Elements Entities people places things entity type is a set of things all of which have the same data properties entity instance is one concrete example of the entity type things that the system keeps track of NOT things that are part of the system Basic Elements cont Relationships show how instances of one entity are related to instances of another entity have cardinality and degree Attributes single pieces of data that describe an instance of an entity like data elements street SSN name city CUSTOMER owner type Has account number ACCOUNT balance Basic ER Diagram Last Maiden Middle Title First Suffix Name CUSTOMER Composite Attribute Last Maiden Middle Title First Suffix Name Deductions EMPLOYEE Multivalued Attribute Effective Date EMPLOYEE Fills POSITION Relationship with an Attribute Effective Date EMPLOYEE Employment History POSITION Associative Entity child parent person parent Unary Relationship type Talent training name Performer address Performs Show dates location Ternary Relationship type Talent name training Has Used in Performer Show address Performs in dates location Three Binary Relationships Effective Date EMPLOYEE Fills POSITION Cardinality Constraints account balance U savings account U account checking account max overdraft interest rate A supertype and subtypes model number model number model number make make price make price price LENS fits uses CAMERA FLASH film type requires requires quantity quantity BATTERY size type model number price PHOTO EQUIPMENT U LENS fits U U make CAMERA uses FLASH film type requires requires quantity quantity BATTERY size type SSN DateEnrolled SSN DateEnrolled Degree STUDENT GRADUATE Graduation Date Grade Grade TRANSCRIPT TRANSCRIPT Date Date COURSE DateEnrolled SSN Grade TRANSCRIPT STUDENT Date COURSE U U Degree CURRENT FORMER Generalization Graduation Date SUPPLIER Wastage SuppliedBy Has Ingredients ITEM Quantity Part of a grocery store database Quantity Has Ingredients ITEM U U U BAKERY ITEM SUPPLIED ITEM SuppliedBy PERISHABLE ITEM Specialization SUPPLIER Wastage DOB DOB PRIMATE Origin LivesIn BIRD HABITAT LivesIn Food LivesIn Food LivesIn 4 LEGGED ANIMAL REPTILE Origin DOB DOB Origin Food Food Part of a Zoo database Origin Origin Food DOB HABITAT U U LivesIn U ANIMAL U PRIMATE BIRD REPTILE 4 LEGGED ANIMAL Specialization Origin DOB Food HABITAT ANIMAL LivesIn Class Replacing a set of subtypes with an attribute model number price PHOTO EQUIPMENT d lens camera fits U U flash U LENS make type type uses CAMERA FLASH film type requires requires Disjoint specialization with discriminator quantity quantity BATTERY size type MOTHER Has OFFSPRING U U d BAD CHILDREN GOOD CHILDREN Total disjoint specialization MOTHER Has SentCard OFFSPRING SentCard U GOOD CHILDREN d No U Yes BAD CHILDREN Total disjoint specialization with discriminator DateEnrolled SSN Grade Enrolled TRANSCRIPT STUDENT Status Date Status Graduated COURSE o Enrolled Y U CURRENT Graduated Y U FORMER Degree Graduation Date Overlapping specialization with discriminator