why do source rpms have "prep" dependencies?

[Mamoru Tasaka]

Robert P. J. Day wrote, at 09/09/2007 04:33 PM +9:00:
>   i wanted to poke around the mkinird source rpm so i downloaded it
> and installed it, and then went to "prep" it via its .spec file:
> 
> $ rpmbuild -bp mkinitrd.spec
> error: Failed build dependencies:
>         parted-devel >= 1.8.5 is needed by mkinitrd-6.0.15-1.fc8.i386
>         libdhcp4client-devel is needed by mkinitrd-6.0.15-1.fc8.i386
>         libdhcp6client-devel is needed by mkinitrd-6.0.15-1.fc8.i386
>         libdhcp-devel >= 1.9 is needed by mkinitrd-6.0.15-1.fc8.i386
>         device-mapper-devel is needed by mkinitrd-6.0.15-1.fc8.i386
> $
> 
>   i'm confused -- why would a source rpm have dependencies for doing a
> simple prep?  for actual building perhaps, but doesn't prepping
> involve simply unloading the tarball and applying the patches?

try:
rpmbuild -bp --nodeps foo.spec

Regards,
Mamoru Tasaka