Discussion
Which of the following best explains why a weak entity must always participate in a total participation relationship with its identifying entity ?
Answer: C
The reason is that weak entities do not have a primary key of their own.
A weak entity's own attributes (its partial key or discriminator) are not enough to identify it uniquely. It is identified only by combining its partial key with the primary key of its owner (identifying) entity. A weak entity instance cannot therefore exist without an owner to borrow that key from, so every instance must take part in the identifying relationship: total participation. A dependent of an employee, for example, is identified by the employee's ID plus the dependent's name.
Weak entities do have attributes, including the partial key. How they are stored in tables is a consequence of the design, not the reason for it, and taking part in several relationships is neither required nor relevant.
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