Belgian shepherd vs sheepdog

Belgian shepherd and sheepdog both are nouns.

Word	Noun	Adjective	Verb	Adverb
Belgian shepherd	Yes	No	No	No
sheepdog	Yes	No	No	No

As nouns, sheepdog is a hypernym of Belgian shepherd; that is, sheepdog is a word with a broader meaning than Belgian shepherd:

Belgian shepherd: hardy working dog developed in Belgium for herding sheep
sheepdog: any of various usually long-haired breeds of dog reared to herd and guard sheep

Other hypernyms of Belgian shepherd include sheep dog, shepherd dog.

Belgian shepherd (noun)	sheepdog (noun)
hardy working dog developed in Belgium for herding sheep	any of various usually long-haired breeds of dog reared to herd and guard sheep