Doubt on a gate question

Question

https://gateoverflow.in/968/gate2003-85

How in the above question the functional dependency (date of birth -> age) is a partial functional dependency. (As told in the selected answer for this question)

Because according to navathe the definition of partial functional dependency is 

A functional dependency X -> Y is a partial dependency if some attribute A belongs to X can be removed from X and the dependency still holds; that is, for some A belongs to X (X - {A}) -> Y.

Comments

 Arjun sir please clarify my doubt.

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DOB is not a total key

Here keys are (Roll_Number, Course_Number,DOB) or (Name, Course_No, DOB)

So, DOB is forming Partial dependency for any key attribute

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@Kushagra Chatterjee,

$Age$ is a Non-Prime Attribute here.

Candidate keys are : $\{ \text{Date_Of_Birth, Name\} } \& \text{ \{Date_Of_Birth, Roll_number}\}$

Now, $Age$ can be determined by the proper subset of both the candidate keys.

So, here partial dependency holds. And hence, the relation is in $1NF$.

$\color{teal}{\text{Suggested Read: }} $ https://gatecse.in/demystifying-database-normalization/

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@Subarna Das I dont have any problem regarding the schema is in 1nf or not I know that it is in 1nf. 

My problem is that in the answer to this question it is written that the dependency (DOB -> age) is a partial dependency.

But if you see the definition given in navathe (written in the question) then (DOB-> age) is not a partial functional dependency. 

Rather I think {DOB, NAME} -> age is a partial functional dependency. 

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@Kushagra Chatterjee

u r right.

moreover,  Here keys are (Roll_Number, Course_Number,DOB) or (Name, Course_No, DOB)

right??

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@Kushagra Chatterjee,

for this FD $\color{red}{\text{\{ Date_Of_Birth} \to \text{Age\}}}$, all the candidate keys are holding partial functional dependency.

So, $\color{violet}{\text{ ( Date_Of_Birth, Name ) }} \& \color{purple}{\text{ ( Date_Of_Birth, Roll_number)}}$ -- both of these are partial functional dependency as $\color{blue}{\text{Date_Of_Birth}}$ is in both of the keys.