When a database designer encounters a multi-valued attribute, which is an attribute that can have multiple values for a single entity instance, there are two courses of action available:
1. Create a new entity: The designer can create a new entity to represent the multi-valued attribute, with a one-to-many relationship between the original entity and the new entity. This allows each value of the multi-valued attribute to be represented as a separate entity instance, which can be linked to the original entity instance.
2. Use a repeating group: The designer can use a repeating group to represent the multi-valued attribute, by including multiple occurrences of the attribute within the same entity. However, this approach can result in data redundancy and can make it difficult to query and maintain the database.
Overall, creating a new entity is the preferred approach, as it allows for better data organization and reduces the risk of data redundancy and inconsistencies.