[Python-Dev] Looking for VCS usage scenarios

Tres Seaver tseaver at palladion.com
Thu Nov 6 13:51:19 CET 2008

Hash: SHA1

Georg Brandl wrote:
> Stephen J. Turnbull schrieb:
>> Tres Seaver writes:
>>  > svn doesn't have any true tags, AFAIK:  everything is a branch.
>> Yow!  I couldn't have imagined that would be true.  And didn't....
> It's not exactly true either. svn doesn't have either tags or branches,
> it has only a single (directory) tree per repository, of which individual
> subdirectories can be checked out individually. This is the root of the
> usual first step in creating a SVN repo: make "branches", "trunk" and
> "tags" subdirs.

The SVN docs use the term "branch" for this concept:


And they document that tags are really branches:


If you have some other definition for "branch", that's fine, but you
will need to outline how that differs from SVN's use of the term, given
that SVN is the reference model for Python development at ths moment.

> In this context it is not surprising that there is no separate branch or
> tag concept. I think the reason is that CVS *had* branches and tags as
> separate concepts and it must have been relatively painful to use them.

At the conceptual level, a tag would be the equivalent of a "symlink",
rather than a copy:  if they existed in SVN, tags would be pointers to
another branch, frozen in at a given revision. The SVN team denies the
utility of tags, which doesn't change the fact that other folks like and
use them effectively in other systems.

Any issues related to the implementation of tags and branches in CVS are
irrelevant to the usefulness of tags:  I have found them very useful in
many other VCSes (ClearCase, Perforce, etc.), and find their deliberate
omission from SVN to be a misfeature.

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Tres Seaver          +1 540-429-0999          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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