What Is Subversion?

Subversion is a source control system like Visual SourceSafe. It keeps track of all versions of a set of source files.

What Is Source Control?

Eric Sink has written an excellent overview of basic source control concepts. You can find it at http://software.ericsink.com/scm/source_control.html .

What Is a Subversion Repository?

A Subversion repository is a collection of all files related to a particular project. You can think of it as an instance of a Subversion database. The FlexWiki repository lives at flexwiki.svn.sourceforge.net, in the folder /flexwiki.

Subversion Philosophy

If you have only ever used Visual SourceSafe in its default configuration for source control, you should be aware that Subversion works quite differently. SourceSafe operates under a "lock-edit-checkin" model, wherein only a developer "checks out" a file, preventing anyone else from working on it, then edits it and ultimately performs a "check in", releasing their lock and allowing the next person to edit the file.

Subversion (like most other source control systems) does not default to this behavior. Rather, it uses a "edit-merge-commit" model. In this model, developers retrieve files from the repository and edit them without locking them. When it comes time to save changes back to the repository, Subversion will check to see if anyone else has made changes to the files you changed while you were working on them. This is called a "conflict", and in many cases Subversion can handle it automatically. If not, the developer can use any one of a number of tools to reconcile any differences and store the merged files back into the repository. This model allows multiple developers to continue working on FlexWiki without anyone blocking anyone else's work.

Other Subversion Terminology

Some of the terms that Subversion uses may be unfamiliar to those who have not worked with Subversion or similar source control systems before.

• Checkout. This is the term that Subversion uses to describe the initial retrieval of a module from a repository. It is a setup step that you will generally only perform once. Note that it does not in any way lock files - it has no relationship with the SourceSafe term "checkout".
• Update. A Subversion update refreshes your local copy from the repository: any files which are newer in the repository will be updated on your hard drive (unless you have also made changes). It is the moral equivalent of the Visual SourceSafe "get latest version" command.
• Commit. A Subversion commit publishes your changes back to the repository where they become available to other developers. It is somewhat similar to a Visual SourceSafe "check in", but since Subversion does not lock files, the analogy does not completely hold.

The usual sequence of events when working with Subversion is:

1. Checkout
2. Edit files
3. Periodically update to pick up changes
4. Commit

Repeating steps 2 through 4 as often as necessary.