At the instance level, are entity occurrences connected to each other by relationship classes (types) defined in the schema?

Introduction / Context:
ER models distinguish between schema-level definitions (entity types and relationship types/classes) and data-level occurrences (entity instances and relationship instances). Understanding this mapping clarifies how actual rows are linked in a database.

Given Data / Assumptions:

• Relationship classes (types) describe allowed associations between entity classes (types).
• For each relationship type, many relationship instances may exist at runtime.
• Relationally, relationship instances are represented via foreign keys or associative tables.

Concept / Approach:
Yes—entity instances are associated through relationship instances that conform to relationship classes. For a binary 1:N, the N-side rows carry a foreign key referencing the 1-side; for M:N, an associative (bridge) table holds pairs of foreign keys. All of these operational links are manifestations of the relationship class defined in the schema.

Step-by-Step Solution:
Define relationship class/type at schema level.Observe data level: each actual link (e.g., an order belonging to a customer) is a relationship instance.Therefore, entity instances are connected by instances of those classes, not ad-hoc.

Verification / Alternative check:
Check sample data: orders.customer_id references customers.id. This FK encodes relationship instances, per the relationship class “Customer places Order.”

Why Other Options Are Wrong:
Limiting to ternary is arbitrary; dismissing relationship types ignores model semantics; nullability is unrelated to whether instances are associated.

Common Pitfalls:
Equating foreign keys with attributes rather than recognizing them as relationship encodings; assuming relationships only exist at design time.

Final Answer:
Valid statement