Attributes on relationships: In ER modeling, is it impossible for relationships to have their own attributes?

Introduction / Context:
While attributes typically describe entities, many real-world facts belong to the association between entities rather than to either entity alone. This question examines whether ER relationships can carry attributes.

Given Data / Assumptions:

• ER models include entities, attributes, and relationships with cardinalities.
• Some relationships represent interactions that have their own properties (e.g., employment with start_date, project assignment with hours_allocated).
• Physical design often maps such relationships to associative tables.

Concept / Approach:
Relationships can indeed have attributes when a property belongs to the association itself. Classic examples include Works_On(Employee, Project) with role or hourly_rate, or Enrollment(Student, Course) with grade. In physical schemas, these become intersection/associative tables with columns for relationship attributes.

Step-by-Step Solution:
Identify properties that do not belong exclusively to either participating entity.Attach those properties to the relationship in the ER model.In the relational design, implement the relationship as an associative table, including keys from both entities and the relationship attributes.Define constraints to protect integrity (e.g., composite primary key, foreign keys).

Verification / Alternative check:
Attempt to place “hours_per_week” on Employee or Project alone; it fails because one employee can have different hours on different projects. The property clearly belongs to the association.

Why Other Options Are Wrong:
Stating it is “always impossible” contradicts common modeling practice. Primary key strategy does not prevent relationship attributes; it guides implementation.

Common Pitfalls:
Forcing relationship attributes onto entities, causing duplication or loss of detail; forgetting to model effective dating where needed.

Final Answer:
Incorrect