You may have noticed by now that Subversion is extremely flexible. Because it implements branches and tags with the same underlying mechanism (directory copies), and because branches and tags appear in normal filesystem space, many people find Subversion intimidating. It's almost too flexible. In this section, we'll offer some suggestions for arranging and managing your data over time.

Repository Layout

There are some standard, recommended ways to organize a repository. Most people create a trunk directory to hold the main line of development, a branches directory to contain branch copies, and a tags directory to contain tag copies. If a repository holds only one project, often people create these top-level directories:


/
   trunk/
   branches/
   tags/

If a repository contains multiple projects, admins typically index their layout by project. See the section called “Planning Your Repository Organization” to read more about project roots, but here's an example of such a layout:


/
   paint/
      trunk/
      branches/
      tags/
   calc/
      trunk/
      branches/
      tags/

Of course, you're free to ignore these common layouts. You can create any sort of variation, whatever works best for you or your team. Remember that whatever you choose, it's not a permanent commitment. You can reorganize your repository at any time. Because branches and tags are ordinary directories, the svn move command can move or rename them however you wish. Switching from one layout to another is just a matter of issuing a series of server-side moves; if you don't like the way things are organized in the repository, just juggle the directories around.

Remember, though, that while moving directories is easy to do, you need to be considerate of other users as well. Your juggling can disorient users with existing working copies. If a user has a working copy of a particular repository directory and your svn move subcommand removes the path from the latest revision, then when the user next runs svn update, she is told that her working copy represents a path that no longer exists. She is then forced to svn switch to the new location.

Data Lifetimes

Another nice feature of Subversion's model is that branches and tags can have finite lifetimes, just like any other versioned item. For example, suppose you eventually finish all your work on your personal branch of the calc project. After merging all of your changes back into /calc/trunk, there's no need for your private branch directory to stick around anymore:

$ svn delete http://svn.example.com/repos/calc/branches/my-calc-branch \
             -m "Removing obsolete branch of calc project."

Committed revision 375.

And now your branch is gone. Of course, it's not really gone: the directory is simply missing from the HEAD revision, no longer distracting anyone. If you use svn checkout, svn switch, or svn list to examine an earlier revision, you can still see your old branch.

If browsing your deleted directory isn't enough, you can always bring it back. Resurrecting data is very easy in Subversion. If there's a deleted directory (or file) that you'd like to bring back into HEAD, simply use svn copy to copy it from the old revision:

$ svn copy http://svn.example.com/repos/calc/branches/my-calc-branch@374 \
           http://svn.example.com/repos/calc/branches/my-calc-branch \
           -m "Restore my-calc-branch."

Committed revision 376.

In our example, your personal branch had a relatively short lifetime: you may have created it to fix a bug or implement a new feature. When your task is done, so is the branch. In software development, though, it's also common to have two main branches running side by side for very long periods. For example, suppose it's time to release a stable version of the calc project to the public, and you know it's going to take a couple of months to shake bugs out of the software. You don't want people to add new features to the project, but you don't want to tell all developers to stop programming either. So instead, you create a stable branch of the software that won't change much:

$ svn copy http://svn.example.com/repos/calc/trunk \
           http://svn.example.com/repos/calc/branches/stable-1.0 \
           -m "Creating stable branch of calc project."

Committed revision 377.

And now developers are free to continue adding cutting-edge (or experimental) features to /calc/trunk, and you can declare a project policy that only bug fixes are to be committed to /calc/branches/stable-1.0. That is, as people continue to work on the trunk, a human selectively ports bug fixes over to the stable branch. Even after the stable branch has shipped, you'll probably continue to maintain the branch for a long time—that is, as long as you continue to support that release for customers. We'll discuss this more in the next section.