Comment 1 for bug 1202309

usr/include/ubuntu for example can be a symlink to the current default level of the sdk for compatability reasons / ease of building against the deefault, e.g.:

usr/include/ubuntu -> usr/include/ubuntu-<version>/ubuntu

The real headers are shipped in: usr/include/ubuntu-<version>/ubuntu/*.h

Then we need to have:
ubuntu-sdk-<version>.pc which define -I /usr/include/ubuntu-<version>
and a default
ubuntu-sdk.pc a symlink to current ubuntu-sdk-<version>.pc.

The ubuntu-sdk-default package will then be the one that ships symlinks only to the current ubuntu-sdk-<version>
This is very similar to how boost-dev, python, python3, etc... are all "dummy" default symlink only packages, depending on the "versioned" default one.