Consider the relation: Movies(title, year, length, genre, studioName, starName)

Question

Consider the relation: Movies(title, year, length, genre, studioName, starName) where title is the title of the movie, year is the year it was released, genre is the genre of the movie (e.g., science fiction, horror,...), studioName is the name of the studio that produced the movie, and starName is the name of a star in the movie.

Describe what real world (if somewhat unlikely) constraint is being captured by each of the following functional dependencies:

genre, starName studioName

year studioName

year, length title

Explanation / Answer

A functional dependancy is a constraint between two sets of attributes in a realtion.

An attribute or set of attributes X is said to Functionally determine another attribute Y if and only if each value X is at most associated with one value of Y. we call X deteminant set and Y independant set.So we can write X -> Y.

Here, we have Realtion Movies(title,year,length,genre,studioName,sratName)

and following FDs can be justified as real word constraint :

1) genre,starName -> studioName

Here, each and every tuple of genre and starName must have at most one value in studioName.

Science,Jack Bratt -> Universal Studio

Genre and starName define unique value from studioName but reverse is not possible as one star can work with multiple studios.

2) year -> studioName

2016 -> Universalstudio

Year is directly functional with universal studio as movie has been relased from that studio in that year.

but reverse is not possible as there are many studios are releasing movies in same year.

3) year,lenght -> title

2016,116 mins -> marsian

here each value of year and length clearly defines unique value with title of the movie.

Please provide any feedback if you want more deep in that.

Thanks.

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