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I am modelling a database for a term project and I have come across something I do not have a definite answer to.

Diagram

I was supplied with the following Entity-Relationship diagram:

Entity-Relationship diagram

Description

So, as you can see, such diagram depicts the following entity types:

  • District, which has the attributes Number(set up as Primary Key), Type and Description.

  • Delegate, that holds the attributes Id (defined as Primary Key), Name, Sex and Description.

Where District is the strong entity type supporting Delegate, but the cardinality of this relationship is 1:1. Up to this point, I have seen 1:M relationship cardinalities regarding strong/weak entities, and I know how to map those to tables, but in this case, I am not so sure, mainly because I do not know how I could get around the possibility of repeating Delegates if the Delegate.Id and the District.Number were to be a composite key.

Questions

  • What shall I do at the implementation level?
  • Do I create a table to store Delegate instances, with the Number of the District as the only key?
  • Is my understanding of composites key wrong?
  • Why deletate is a weak entity? Delegates seems entities of their own, that can be identified by their attributes alone, independently from the district. – Renzo Mar 24 '16 at 11:37

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