The Zachman Framework(TM) for Enterprise Architecture is something we've always been inspired by, since it summarizes the multiple dimensions (and perspectives) that are important to defining the enterprise perspective. It is both, simple and overwhelming at the same time. (But, then, no one ever said architecting was simple!).
Architecture - in the broadest sense - may mean different things, depending on the perspective and who (i.e which role) is the stakeholder. The Zachman Framework(TM) throws up a number of debates and this article by John Zachman, discusses the finer distinctions between the three main perspectives: Conceptual, Logical and Physical.
Yes, architecture is relative, but it is not arbitrary. As long as we continue to consider it arbitrary, we are going nowhere. We are just adding to the legacy. “Keeping on doing the same thing and expecting different results is one definition of insanity” (Einstein)