Which of the following mappings between OutSystems and the Database is NOT correct?

The reasoning for identifying the reference attribute as not being a direct mapping to a primary key is key to understanding database structures within the OutSystems platform. In OutSystems, entities are mapped to tables in the underlying database, which corresponds correctly with options indicating entities as tables and attributes as columns since these terms reflect the basic architecture of relational databases.

However, the term "reference attribute" specifically refers to an attribute that defines a relationship between entities — essentially, it acts as a foreign key rather than a primary key. In relational database design, a primary key uniquely identifies each record within a table, while a foreign key serves to link two tables together, establishing relationships rather than defining the uniqueness of records within a single table.

So, the distinction lies in the roles that primary keys and foreign keys play: primary keys enforce uniqueness within a table, while reference attributes (or foreign keys) point to another table's primary key, creating a relational link between the two entities. Recognizing this difference is crucial for anyone working with relational database concepts in OutSystems.