How objective can the analysis of a notated piece of music into a hierarchical structure of some "constituents" be?
Consider a given piece of music in notated form and structurally analysed by different experts. How strongly will their analyses probably agree? And if they don't agree: How commensurable will their analyses be (maybe just focussing on different aspects)?
Any analysis obviously depends on the ontology and terminology of the analyzer, but I assume that very many musical ontologies contain equivalents of "voices/instruments", "tones", "intervals", "melodies", "chords", "rhythms", some kind of "motifs" and "transitions", and some kind of "parts" (of longer pieces of music).
I assume that the "objectiveness" of the structure of a piece of music somehow depends on the composer and his or her epoch and style. There may be more "mathematically" inclined epochs and composers – like J.S. Bach, whose compositions have a rather clear-cut structure – and more "anarchistic" composers for whom it is hard to tell an "objective" structure of their compositions (e.g. free jazzers like John Coltrane).
I admit that the question is not very sharp and answers will have to be opinion-based. But maybe someone dares to give an authorative answer like "most structural analyses of notated pieces of music - if they exist - do essentially agree (at least for the music of composer XY or epoch YZ)."