As discussed on the Style ML: http://musicbrainz.1054305.n4.nabble.com/WI-12-Work-Titles-that-are-part-of-an-Aggregate-Work-td3774919.html

Currently, when joining parts of a classical work, the sub-work must contain the aggregate work title + sub-work title. We need a way to stop copying the redundant parent work title information in the sub-works.

Example:
This work is titled: Symphony No. 5 in C minor, Op. 67
And has 4 sub-parts (in this case movements):

• Allegro con brio
• Andante con moto
• Scherzo. Allegro
• Allegro

At the moment we have to title it like this:

Symphony No. 5 in C minor, Op. 67 (Aggregate, parent work)
Symphony No. 5 in C minor, Op. 67: I. Allegro con brio
Symphony No. 5 in C minor, Op. 67: II. Andante con moto
Symphony No. 5 in C minor, Op. 67: III. Scherzo. Allegro
Symphony No. 5 in C minor, Op. 67: IV. Allegro

I think we should eventually move to a point where we don't need to repeat the aggregate part of every sub-work.
Ideally the sub-works should simply be:
I. Allegro con brio
II. Andante con moto
III. Scherzo. Allegro
IV. Allegro

The full title of the sub-work should be constructed by joining the aggregate work title + sub-work title.
I think the manner this should be implemented is similar to how we join artists in the AC field, where we could perhaps even choose the linking form, (in the above example, it should probably be ": " or ", "

Some pretty significant changes will need to be done to MB before this can be done however:
1.) When searching, MB should list the results using the Full work title including aggregate.
2.) Same when on the sub-work page
3.) The sub-works need to be grouped and hidden under the aggregate work. (I opened a ticket for this already: http://tickets.musicbrainz.org/browse/MBS-2637)
4.) Picard (and other tagging programs) need to be aware of the modification and tag accordingly.

There are numerous advantages to this proposal, one very obvious example is that if we need to make a modification to the aggregate work title, we don't need to follow through and change ALL sub-works.

As we continue in the cleanup of classical works, there will be many instances where there will be 3 levels of works in the hierarchy. if this ticket gets implemented, this will benefit these works even more.
A few examples of multi-level works:
http://musicbrainz.org/work/d8b0318b-0a84-49e9-8d08-152e8cdc874b
http://musicbrainz.org/work/bfe25ab1-204f-4dc0-a2d5-c9a14c9339b1