What is the key for this relation?

farfrom

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ERD

ERD (Entity Relationship Diagram)

Please look at the ERD http://www.mepopo.com/image/1/38504 If I mapping the ERD into relational database schema R(k1, k2, k3, a, b) (which is before normalization). What will be the key for R? Thanks a lot! Jean

Asked: June 11, 2013 4:55 AM Last updated: June 11, 2013 12:06 PM

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CharlieBrowne Jun 11, 2013 12:40 AM GMT

This seems to be a homework question and we do not do homework. How about you give us your answer and explain your reasoning for your choice. We may help you out then.

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farfrom Jun 13, 2013 2:22 AM GMT

Hi Charlie, Thanks for your reply. Since I am learning Database from some book, and there is a passage about how to mapping ERD to relational schema, about N-ary relationship too few examples for me to clear the concept, I search from web to find this question. According my learning, the key is k3, because the cardinality constraints for the other two participating entity types E1, E2 are both "1" , only the cardinality constraints on E3 is "N". This is my answer, is it right? and also , is this means any relationship instance in E3 uniquely determines the instance of E1,E2 combination ? Thanks in advance Jean

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