This seems to be a work-attribute example. However...
The missing example at the end has helped me see why a relationship-based model might possibly be better - because it would allow a work to have several different types, though I am unclear whether there are actually such examples, and if there are whether it would make more sense to think of them as separate arrangements of the same work.
However, I think that relationship-attributes have a fundamental flaw.They would either need to have attributes for both ends of the relationship, in which case you can easily get conflicts between relationships saying different things about the same work - OR they would only describe e.g. the lower end of the relationship in which case you will have one less attribute than the number of works. Based on this, I think we should stop considering relationship attributes as a solution and focus on work attributes.
Taking this example as a basis, my proposal would be as follows:
Concerto in E major, op. 8 no. 1, RV 269 “La primavera”: I. Allegro
is part of:
Concerto in E major, op. 8 no. 1, RV 269 “La primavera”
TYPE: Not sure - it is not really a complete work (as commonly understood) itself, because it is really part of "4 Seasons". I guess this demonstrates the difficulties of getting this right. Perhaps the suggestion of Concerto is a good idea, but then what do you call the parent(s), and how many alternatives do you need (Symphony, Opera are obvious other values, but I suspect you will still need a catch-all for music which doesn't fit.)
is part of TWO higher level works:
Le quattro stagioni (“The Four Seasons”)
Type: Main Work
Il cimento dell'armonia e dell'inventione, op. 8
Type: Main Work
Perhaps Wagner Ring Cycle would be another useful example, in part because of the number of levels of work it has.