Thanks for it.
As I wrote in my Edit, the alternative would have been be to create a (sub-)Work for each Livre (book). They could have been related to the main work and, possibly to the composer, to his two works catalogue, L. and CD, with the number “CD 143”, “CD 143-I”/“CD 143-II”, “CD 143 (L1)”/“CD 143 (L2)”, etc. for example (highly debatable proposals!).
Personally, I do not like such a multiplication of Works, when it is just a way to structure a rather complex Work made of several parts, sub-parts, etc., like an e.g. operas, set of songs, suites, etc. especially when there are different possible ways to consider this structure, i.e. different possible arrangement of sub-works.
In Debussy’s Études case, the Livre level could be considered as optional: some could consider that the work Douze Études is made up of 12 Études, column. Others may consider that the Douze Études are undoubtedly comprised of 2 Livres each one including 6 Études.
Should then the Études works be related to both upper-level Works: to the intermediate one Livre and to the top one Douze Études? Here we have only 3 levels in the tree structure, of which only one is optional; what about a more complex situation when there would be 5 levels, of which 2 or 3 are optional, and possibly interwoven…
For sure, the Series is not the perfect answer to my wish of avoiding Works. With a Series, there is no AR with a parent work, neither to the composer artist (or only as the Cataloguer, which is wrong)… Moreover, there is no Series type that corresponds to this purpose. I intently used the “Series of Works” rather the “A series of works which form a catalogue of classical compositions”.
But I thought it would a be an appropriate (maybe temporary) way to record the existence of this intermediate level Livres.
I would be happy if this discussion led to an improvement of the Schema, to better manage works structuring.