architecture vs subject area

architecture and subject area both are nouns.

Word	Noun	Adjective	Verb	Adverb
architecture	Yes	No	No	No
subject area	Yes	No	No	No

As nouns, subject area is a hypernym of architecture; that is, subject area is a word with a broader meaning than architecture:

architecture: the discipline dealing with the principles of design and construction and ornamentation of fine buildings
subject area: a branch of knowledge

Other hypernyms of architecture include bailiwick, discipline, field, field of study, study, subject, subject field, beaux arts, fine arts.

architecture (noun)	subject area (noun)
the profession of designing buildings and environments with consideration for their esthetic effect	a branch of knowledge
an architectural product or work
(computer science) the structure and organization of a computer's hardware or system software
the discipline dealing with the principles of design and construction and ornamentation of fine buildings