CODEWITHSUNDEEP
mysqlsqldatabase-designdata-modeling
TheKraven
TheKraven

Reputation: 583

Parent and child entities in one to one relationships

The entity which participates in the 1:0+ relationship is the parent entity.

Is that correct?

Update:

Image provided

Upvotes: 0

Views: 2348

Answers (1)

Polynomial
Polynomial

Reputation: 28316

No, this is wrong.

In a 1:1 relationship, you just have one table. There's no distinction. The attributes must apply to both types of entity.

However, in an optional 1:1 relationship, often called 1:0+ or "one to zero or one" relationship, the child would be the optional one, not the parent.

In short, there will always be a parent.

In your image, there's an optional one-to-one from staff to notebook, i.e. a staff member may have zero notebooks or one notebook. There's also a one-to-one relationship from notebook to staff, i.e. a notebook must have exactly one member of staff as an owner.

Here's a diagram to help you understand:

Crow's Foot

Upvotes: 4

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