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INFO210_HW2_solution

# Every professor must teach some course solution a

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Unformatted text preview: nship. Participation constraints may not hold, as in (d) above, however, key constraints always do. Part 2 (15pts) A university database contains information about professors (identified by social security number, abbreviated ssn) and courses (identified by cid). Professors teach courses. Each of the following situations concerns the teaches relationship set. For each situation, draw an ER diagram that describes it, assuming that no further conditions hold. Mark all key and participation constraints. (a) Professors can teach the same course in several semesters, and each offering must be recorded. Solution: A ternary relationship with no key or participation constraints. ssn' cid' COURSE' teaches' PROFESSOR' year' quarter' TERM' (b) Professors can teach the same course in several semesters, and only the most recent offering must be recorded. Solution: A binary relationship in which no key or participation constraints hold. ssn' year' quarter' COURSE' teaches' PROFESSOR' cid' (c) Professors can teach the same course in several semesters, and only the most recent offering must be recorded. Every professor must teach some course. Solution: A binary relationship with a participation constraint over the entity set professors. ssn' PROFESSOR' year' quarter' teaches' cid' COURSE' (d) Professors can teach the same course in several semesters, and only the most recent offering must be recorded. Every professor must teach exactly one course. Solution: A binary relationship with a key and a participation constraint over the entity set profess...
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