realm vs knowledge base

realm and knowledge base both are nouns.

Word	Noun	Adjective	Verb	Adverb
realm	Yes	No	No	No
knowledge base	Yes	No	No	No

As nouns, knowledge base is a hypernym of realm; that is, knowledge base is a word with a broader meaning than realm:

realm: a knowledge domain that you are interested in or are communicating about
knowledge base: the content of a particular field of knowledge

Other hypernyms of realm include domain, knowledge domain.

realm (noun)	knowledge base (noun)
a knowledge domain that you are interested in or are communicating about	the content of a particular field of knowledge
the domain ruled by a king or queen
a domain in which something is dominant