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Data Modeling and Relational Database Design
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Analyze and model the relationships between entities Draw an initial entity relationship diagram Read the relationships on an ER diagram Clearly define relationship names Analyze and model the relationships between entities Draw an initial entity relationship diagram Read the relationships on an ER diagram Clearly define relationship names
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The way one entity relates to another The business rules that link together business information needs What one thing has to do with another A named association between entities The way one entity relates to another The business rules that link together business information needs What one thing has to do with another A named association between entities
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DMDD COURSE SMT COURSE INSTRUCTORCOURSE
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A line between two entities Lower case relationship name Optionality (Minimum cardinality) A line between two entities Lower case relationship name Optionality (Minimum cardinality) Degree (Maximum cardinality) Optional - may be Mandatory - must be One or more One and only one
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COPY TITLE many (crow’s foot) mandatory optional one
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Each Subject entity must be or may be relationship name one or more or one and only one entity 1entity 2 Degree Object entity Optionality Name
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EMPLOYEE DEPARTMENT assigned to
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EMPLOYEE DEPARTMENT assigned to Each EMPLOYEE must be assigned to one and only one DEPARTMENT
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EMPLOYEE DEPARTMENT responsible for
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EMPLOYEE DEPARTMENT Each DEPARTMENT may be responsible for one or more EMPLOYEES responsible for
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EMPLOYEE DEPARTMENT assigned to Each EMPLOYEE must be assigned to one and only one DEPARTMENT EMPLOYEE DEPARTMENT Each DEPARTMENT may be responsible for one or more EMPLOYEES responsible for
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taken by enrolled in STUDENT COURSE
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Each STUDENT may be enrolled in one or more COURSES Each COURSE may be taken by one or more STUDENTS taken by enrolled in STUDENT COURSE
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Many-to-One One-to-One Many-to-Many
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CUSTOMER SALES REPRESENTATIVE assigned to visited by
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PATIENT HEALTH CARE WORKER assigned to attended by
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BICYCLECYCLIST the rider of is ridden by Represents a snapshot in time
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1 Determine the existence of a relationship 2 Name each direction of the relationship 3 Determine the degree of each direction of the relationship 4 Determine the optionality of each direction of the relationship 5 Read the relationship aloud to validate it 1 Determine the existence of a relationship 2 Name each direction of the relationship 3 Determine the degree of each direction of the relationship 4 Determine the optionality of each direction of the relationship 5 Read the relationship aloud to validate it
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Existence Name Optionality Degree Validate MEMBERSHIP COPY RENTAL MEMBERSHIP RENTAL MEMBERSHIP COPY
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Existence Name Optionality Degree Validate COPY TITLE of available as Each title is available as a copy and each copy is of a title
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Name Optionality Degree Validate Existence COPY TITLE one many Each title is available as a copy, there could be lots of copies but there is only ever one title on a copy
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Existence Name Optionality Degree Validate optional mandatory COPY TITLE Every copy must have a title on it but we need information about titles even if there is no copy
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Existence Name Optionality Degree Validate COPY TITLE of available as Each copy must be of one and only one title, and each title may be available as one or more copies
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Establish the existence of a relationship Name the relationship Determine its degree Determine its optionality Read the relationship to validate it Establish the existence of a relationship Name the relationship Determine its degree Determine its optionality Read the relationship to validate it
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