How do I identify the partial key of a weak entity set?

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I've a weak entity set as follows:
Medicine_reminder that have three attribute : start_date,dosage , and time
I am unable to define the partial key for this.

What I have tried:

I thought of taking it as multivalued composite attribute but that doesnt work

Posted 25-Jul-22 5:23am

Aditi Thakore

Updated 25-Jul-22 20:21pm

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Gerry Schmitz · Answer 1 · 2022-07-25T20:21:00

Start_date is a partial key; the entity is not unique without the time (e.g. the prime key is date+time). The name medicine "reminder" provide a hint as to context.

Partial keys are often used in "starts with" type searches, and can make use of existing "full" (key) indexes for optimization.