database schema and foreign key -

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i couldn't figure out. i'm not @ database design. can explain me?

diagram

answers

1) relationship “assigned to” between blob , thing 1:m 1 blob can have 0 or many things. in database theory foreign key goes many side. therefore blob can have 2 columns.

2)

a) no fk – same explanations in question 1

b) parta , partb – same explanation in question 1 , since thing has composite key (entity needs more 1 attribute identify tuples uniquely) both underlined column names has given

notes

1) er diagram uses crow notation

2) end product of er diagram relational schema diagram relationships appear in relational schema foreign keys.


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