A very nice explanation of how this evolved: http://unix.stackexchange.com/questions/44271/why-do-package-names-contain-version-numbers
Even though it is theoretically possible to install multiple versions of the same package on the same host, in practice this adds complications. So even though rpm itself will happily install multiple versions of the same package, most higher level tools (like yum, or apt), will not behave nicely. Their upgrade procedures will actively remove all older versions whenever a newer one is installed.
The common solution is to move the major version into the package name itself. Even though this is arguably a hack, it does express the inherent quality of incompatibility when doing a major version change to a piece of software.
According to the semantic versioning spec, a major version change:
Major version X (X.y.z | X > 0) MUST be incremented if any backwards incompatible changes are introduced to the public APIA new major version will break non-updated consumers of the package. That's a big deal. In practice, you will not be able to perform a major version update without some form of transition plan, during which both the old and the new version must be available.
Note that you can make different choices. A very common choice is to maintain a policy of always preserving compatibility to the previous version. This gives every consumer the time to upgrade.
In either case, there is no need to keep the major version number in the version string. If you're a good citizen and always maintain backwards compatibility, your major version is stuck at "1" forever, not adding anything useful - and if you change the package name whenever you do break backwards compatibility, you don't need it anyways...
So, how about finding a nice funeral home for the major version number?
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