Some compositions are presented on a CD as multiple tracks, even though those tracks are really meant to be played together.  This happens most frequently in classical music, with symphonies, sonatas, etc., but it also happens in popular music on occasion ("Mean Mr. Mustard/Polythene Pam/..." by the Beatles, "2112" by Rush).

I would like for there to be an optional mechanism within slimserver that would treat such multi-track compositions as a single "song" for the purposes of "shuffle by song" or when adding to a playlist while browsing through the collection.  This would be similar to the way multi-disc albums are treated as a single album by slimserver now.

I have imagined three different ways to tag a track to indicate that it is part of a multi-track composition, each with its own advantages and drawbacks.  In all cases, there is a title for the overall composition and a title for each track corresponding to the movement or part.

1) Include both the title of the composition and the part information are stored in the TITLE tag, using a specific syntax that slimserver can read:

TITLE=Symphony No. 9 (2/5=ii. Molto Vivace)

The advantage here is that other players can read the tag directly and all the information is there.
The disadvantage is that the user must construct the syntax manually, and there could be confusion if someone uses a similar syntax for some other purpose.

2) Invent a user-defined tag called WORK or COMPOSITION for the title of the composition, and use TITLE tag for the movement title.  In this case, the order of the movements would be determined by the TRACKNUMBER tag, which would not necessarily start with 1.

WORK=Symphony No. 9
TITLE=ii. Molto Vivace

This is nice because it gives a unique TITLE for each track so that other players can keep it sorted out, but has the disadvantage that said player will not be able to tell you which composition it belongs to.

3) Invent a user-defined tag called PART for the title of the movement, and use the TITLE tag for the composition.  Again, movement order would be determined by TRACKNUMBER.

TITLE=Symphony No. 9
PART=ii. Molto Vivace

The advantage here is that the tag for the grouping is the same level as the tag for a single-track song, so "shuffle by song" would be the same as "shuffle by TITLE".  That may or may not make coding easier.  Another advantage is that the TITLE display on other players will show the name of the composition, with the drawback that the movement number and title are lost.  Also, browsing on other players will be compromised because all tracks in a composition will show up with the same title.  The user might be able to tell which is which if the browse list is sorted by track number.

There is a group of people who are already using "WORK" and have created a script for assembling a shuffled playlist based on that tag: http://forums.slimdevices.com/showthread.php?t=22079

One final note:
For classical music, some people (including myself) have adopted a compromised tagging strategy of using the ALBUM tag as the title of a composition, with the TITLE tag as the title of the movement.  This has several drawbacks.  First of all, it does not provide the shuffle behavior I described in the 2nd paragraph -- "shuffle by album" is required to get the whole composition at once, and results in individual classical compositions being mixed in with entire pop albums.  "Shuffle by song" results in single classical movements being played separately, mixed in with pop songs.  The other drawback is that the cohesion of the original physical CD album is lost.  I can't play "Wynton Marsalis -- Baroque Music for Trumpets" unless I remember which compositions were on that album and assemble the playlist myself.