arts vs library science

arts and library science both are nouns.

Word	Noun	Adjective	Verb	Adverb
arts	Yes	No	No	No
library science	Yes	No	No	No

As nouns, library science is a hyponym of arts; that is, library science is a word with a more specific, narrower meaning than arts:

arts: studies intended to provide general knowledge and intellectual skills (rather than occupational or professional skills)
library science: the study of the principles and practices of library administration

arts (noun)	library science (noun)
studies intended to provide general knowledge and intellectual skills (rather than occupational or professional skills)	the study of the principles and practices of library administration