Final answer:
The correct statement about a weak entity set is that the key of a weak entity set includes all key attributes from supporting entity sets. This combination (the weak entity's attributes plus those from its strong entity) is known as a partial key.
Step-by-step explanation:
The correct statement about a weak entity set is that the key of a weak entity set includes all key attributes from supporting entity sets. A weak entity cannot be uniquely identified by its attributes alone, therefore it relies on a supporting entity set (also known as a strong entity set) and is typically associated with a 'supporting relationship'.
For clarification, let's examine each option from the question:
- a. Weak entity set can have only one supporting relationship: This is not necessarily true, as a weak entity set could potentially be supported by more than one relationship in complex data models.
- b. None of the others: This option is not helpful without knowing the context of 'the others.'
- c. Weak entity set cannot have more than one supporting entity set: This statement is too restrictive. While a weak entity set primarily depends on one particular strong entity set with a supporting relationship, it may also have associations with other entities.
- d. The key of weak entity set includes all key attributes from supporting entity sets: This is the correct statement. This combination of the weak entity's attributes and the key attributes of its supporting entity set is known as a partial key, which uniquely identifies records within the weak entity set.