To take a specific example, Pergolesi wrote a setting of the hymn ‘Stabat Mater’ (which is fantastic). So that’s the composition. But it can sound very different depending on how it is performed, my favourite performance is by Emma Kirkby. But it’s hit and miss about how that gets categorised - and it’s particularly important if the piece forms part of a set of works. I don’t want to search Emma Kirkby to find a piece by pergolesi, and I want to be able to group by composer rather than performer even through the performer is listed as the artist. Or, I might want to find other pieces performed by her from other composers.