What is the function of a primary key in a CDT?

A primary key in a Complex Data Type (CDT) serves the essential function of uniquely identifying a row of data within that structure. This unique identification is critical because it ensures that each record can be accessed and referenced individually, making operations such as querying, updating, and deleting records straightforward and reliable.

When a primary key is defined, it eliminates ambiguity when dealing with multiple records by ensuring that no two rows share the same key value. This uniqueness allows for efficient data management and integrity, as it prevents duplication and allows for precise reference in data operations.

In contrast, the other choices pertain to different aspects of data management. For instance, linking multiple records relates to relationships between different data entries, while defining data types involves specifying the nature of the data contained in the CDT. Enforcing data relationships speaks to the connections between different data structures rather than focusing on unique identification within a single structure. Thus, the function of a primary key specifically revolves around unique identification, making option B the correct choice.