Final answer:
Two conditions must be met before an entity can be classified as a weak entity: it must have a partial identifier and a strong entity.
Step-by-step explanation:
Before an entity can be classified as a weak entity, two conditions must be met:
A weak entity must have a partial identifier, which means that it cannot be uniquely identified without the help of another entity's identifier.
A weak entity must also have a strong entity, which is the parent entity that provides the unique identifier for the weak entity.
For example, consider an entity relationship diagram for a library database. The 'BookCopy' entity could be classified as a weak entity because it relies on the 'Book' entity's identifier ('ISBN') to be uniquely identified.