Introduction to E-R Concepts

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Assume you are asked to design a simple registration database, where students can enroll in courses. Below give the result relational tables and E-R (Entity-Relationship) diagram, where

• ▭ is an entity,
• ◇ is a relationship,
• ⬭ is an attribute, and
• (minimum cardinality, maximum cardinality). Cardinality expresses the specific number of entity occurrences associated with one occurrence of the related entity; e.g., a minimum cardinality of 0 indicates that the relationship is optional.

⇓ Transforming (N-N relationship)

student sid lname fname class telephone 1 Jones Allan 2 555-1234 2 Smith John 3 555-4321 3 Brown Harry 2 555-1122 5 White Edward 3 555-3344 course cno cname croom time 101 French I 2-104 MW2 102 French II 2-113 MW3 105 Algebra 3-105 MW2 108 Calculus 2-113 WM4

enrollment sid cno major 1 101 No 1 108 Yes 2 105 No 3 101 Yes 3 108 No 5 102 No 5 105 No