What does a one-to-many (1:M) relationship in an Entity-Relationship Diagram (ERD) indicate?

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BlackTom AI · Accepted Answer

Here’s a breakdown of what each option implies about a one-to-many (1:M) relationship in an ERD and why it is or isn’t accurate.

Option a: 'One attribute is split into many columns' — This describes a normalization/columnar issue or a design pattern where an attribute is deconstructed across columns, but it does not characterize entity relationships. It misstates the concept of 1:M by focusing on attributes and columns rather than how entities relate to each other. Therefore this option is inaccurate for describing 1:M.

Option b: 'One entity is linked to exactly one other entity' — This assertion corresponds to a one-to-one (1:1) relationship, where each instance of the first entity relates to exactly one instance of the second entity. It contradicts the meaning of 1:M, which allows a single instance on the 'one' side to relate to many instances on the 'many' side. Hence this option is incorrect when explaining 1:M.

Option c: 'One instance of an entity can be related to many instances of another entity' — This captures the core idea of a 1:M relationship. It states that a single record in the first entity (the 'one' side) can be associated with multiple records in the second entity (the 'many' side), which is the defining feature of 1:M in ER diagrams. This statement aligns with standard ER modeling concepts.

Option d: 'Many databases are combined into one' — This describes a data consolidation or integration idea, not an ERD relationship between two entities. It has no bearing on the nature of a 1:M relationship and is therefore incorrect in this context.

In summary, the most accurate depiction of a one-to-many relationship is that a single instance of an entity can be related to multiple instances of another entity, which is what option c expresses. The other options mix in concepts from attributes, one-to-one relationships, or broader data management ideas that do not define 1:M in an ER diagram.

MCD1470 Engineering Practices / MCD4770 Professional Practice - Trimester 2 - 2025

What does a one-to-many (1:M) relationship in an Entity-Relationship Diagram (ERD) indicate?

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