All split packages which were build with the same PKGBUILD share the same pkgbase in their .PKGINFO file. But one direction is missing: Giving a single split package file one cannot tell which other packages were build with the same PKGBUILD.

The solution would be somehow add the complete list of pkgnames to each package's .PKGINFO file. I am only unsure about the key one should use here and whether this list should include the package's own pkgname or not.

ATM I see two possible usages for this information:
* check whether a split package is missing in the staging dir on db-update
* check whether a split package has been removed on db-update

The second task would even be muh easier if that information would also be put into the db files. (pacman might use this information, too) This might be redundant though as one could also get the same information by scanning the db file for a given pkgbase and output the related pkgname.