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POStill Confused About Identifying vs. Non-Identifying Relationships
 

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  1. POStill Confused About Identifying vs. Non-Identifying Relationships
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    <p>So, I've been reading up on identifying vs. non-identifying relationships in my database design, and a number of the answers on SO seem contradicting to me. Here are the two questions I am looking at:</p> <ol> <li><a href="https://stackoverflow.com/questions/762937/whats-the-difference-between-identifying-and-non-identifying-relationships">What's the Difference Between Identifying and Non-Identifying Relationships</a></li> <li><a href="https://stackoverflow.com/questions/1216805/trouble-deciding-on-identifying-or-non-identifying-relationship">Trouble Deciding on Identifying or Non-Identifying Relationship</a></li> </ol> <p>Looking at the top answers from each question, I appear to get two different ideas of what an identifying relationship is.</p> <p>The first question's response says that an identifying relationship "describes a situation in which the existence of a row in the child table depends on a row in the parent table." An example of this that is given is, "An author can write many books (1-to-n relationship), but a book cannot exist without an author." That makes sense to me.</p> <p>However, when I read the response to question two, I get confused as it says, "if a child identifies its parent, it is an identifying relationship." The answer then goes on to give examples such as <a href="http://en.wikipedia.org/wiki/Social_Security_number" rel="nofollow noreferrer">Social Security Number</a> (is identifying of a Person), but an address is not (because many people can live at an address). To me, this sounds more like a case of the decision between primary key and non-primary key.</p> <p>My own gut feeling (and additional research on other sites) points to the first question and its response being correct. However, I wanted to verify before I continued forward as I don't want to learn something wrong as I am working to understand database design. Thanks in advance.</p>
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