lecture-10-er-diagrams-continued

lecture-10-er-diagrams-continued - The Entity-Relationship...

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The Entity-Relationship Model Continued T. M. Murali September 27, 2010 T. M. Murali September 27, 2010 CS 4604: E/R model
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Roles in Relationships I Can the same entity set appear more than once in the same relationship? T. M. Murali September 27, 2010 CS 4604: E/R model
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Roles in Relationships I Can the same entity set appear more than once in the same relationship? I Prerequisite relationship between two Courses PreReq Courses Enrollment Classroom Name I Which course is the pre-requisite? T. M. Murali September 27, 2010 CS 4604: E/R model
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Roles in Relationships I Which course is the pre-requisite? I Label the lines connecting entity to relationship with the role of the entity. Requirement Requirer PreReq Courses Enrollment Classroom Name T. M. Murali September 27, 2010 CS 4604: E/R model
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Parallel Relationships I Can there be more than one relationship between the same pair of entities? T. M. Murali September 27, 2010 CS 4604: E/R model
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Parallel Relationships I Can there be more than one relationship between the same pair of entities? I TA and Take relationship between Students and Classes Courses TA Take Students T. M. Murali September 27, 2010 CS 4604: E/R model
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Are Attributes on Relationships Needed? Students Courses Take Name Address Enrollment Classroom Name Grade T. M. Murali September 27, 2010 CS 4604: E/R model
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Are Attributes on Relationships Needed? Students Courses Take Name Address Enrollment Classroom Name Grade I We can convert the attribute to an entity and make the relationship multiway. Students Courses Take Name Address Enrollment Classroom Name Grade Grade T. M. Murali September 27, 2010 CS 4604: E/R model
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Multiway Relationships I Relationships may connect more than two entity sets. I Consider scenario two in the handout: 1 professor can teach a course but each student evaluates each professor separately. T. M. Murali September 27, 2010 CS 4604: E/R model
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Multiway Relationships I Relationships may connect more than two entity sets. I Consider scenario two in the handout: 1 professor can teach a course but each student evaluates each professor separately.
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