File and Directory Ownership
Your package should own all of the files that are installed as part of the %install process. Packages must not own files already owned by other packages. The rule of thumb here is that the first package to be installed should own the files that other packages may rely upon. This means, for example, that no package in Fedora should ever share ownership with any of the files owned by the filesystem or man package. If you feel that you have a good reason to own a file or that another package owns, then please present that at package review time.
Directory ownership is a little more complex than file ownership. Although the rule of thumb is the same: own all the directories you create but none of the directories of packages you depend on, there are several instances where it's desirable for multiple packages to own a directory. Examples of this are:
1) The package you depend on to provide a directory may choose to own a different directory in a later version and your package will run unmodified with that later version.
One common example of this is a Perl module. Assume perl-A-B depends on perl-A and installs files into /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi/A/B. The base Perl package guarantees that it will own /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi for as long as it remains compatible with version 5.8.8, but a future upgrade of the perl-A package may install into (and thus own) /usr/lib/perl5/vendor_perl/5.9.0/i386-linux-thread-multi/A. So the perl-A-B package needs to own /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi/A as well as /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi/A/B in order to maintain proper ownership.
2) Multiple packages have files in a common directory but none of them requires others.
An example:
Foo-Animal-Emu puts files into /usr/share/Foo/Animal/Emu Foo-Animal-Llama puts files into /usr/share/Foo/Animal/Llama
Neither package depends on the other one. Neither package depends on any other package which owns the /usr/share/Foo/Animal/ directory. In this case, each package must own the /usr/share/Foo/Animal/ directory.
In all cases we are guarding against unowned directories being present on a system. Please see Packaging:UnownedDirectories for the details.