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PODatabase modeling for a weak entity
 

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    <p>I have 2 tables in my database <code>orders</code> and <code>orderHistory</code>. </p> <pre><code> ----------------- ----------------------- | orders | | orderHistory | ----------------- ----------------------- | orderID (PK) | | historyLineID (PK) | | orderDate | | status | | price | | quantity | ----------------- ----------------------- </code></pre> <p>Now an <code>order</code> can have multiple <code>history lines</code>. However, a <code>history line</code> can't exist on its own. I heard this is called a weak entity and therefore the <strong>PK</strong> from <code>orders</code> must be part of the <strong>PK</strong> of table <code>orderHistory</code>.</p> <p><strong>Questions</strong></p> <ol> <li>Is this really a correct <em>weak entity</em> relationship? Is there other ways to identify them?</li> <li>Should I add the <strong>PK</strong> of table <code>order</code> to table <code>orderHistory</code> and make it a composite primary key?</li> <li>In case I decide to add a new record to <code>orderHistory</code>, how will I add a new composite key? (<code>orderID</code> is available from table <code>orders</code>, but <code>historyLineID</code> should be auto incremented.) </li> <li>What if I decide to model this as a normal <strong>One-To-Many</strong> relationship where <code>orderID</code> is added as a foreign key <strong>only</strong> instead? what are the cons of doing so?</li> <li>Will ignoring Weak entities at all cause any problems later in a design provided all tables are in 3rd normal form?</li> </ol> <p><strong>Note</strong></p> <p>Both <code>orderID</code> &amp; <code>historyLineID</code> are surrogate keys. Thanks in advance.</p>
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