Approaches to music
encoding
§
§audio / performance
§notation / written artefact
§selection depends on definition of "musical work"
§
Almost any musical work can be performed in a variety of ways. So a performance, even one by the composer, is not the work itself.  Music notation can represent a work, but there can be several equally valid ways of writing down the same thing.  Therefore, a score is not the work either.  Perhaps it is most accurate to say that a score or a performance represents an instance of a work, which is a concept, not a physical entity.