This chapter is a short, casual introduction to Subversion.
If you're new to version control, this chapter is definitely for
you. We begin with a discussion of general version control
concepts, work our way into the specific ideas behind
Subversion, and show some simple examples of Subversion in
use.
Even though the examples in this chapter show people sharing
collections of program source code, keep in mind that Subversion
can manage any sort of file collection—it's not limited to
helping computer programmers.
Subversion is a centralized system for sharing information.
At its core is a repository, which is a central store of data.
The repository stores information in the form of a
filesystem tree—a typical hierarchy
of files and directories. Any number of
clients connect to the repository, and
then read or write to these files. By writing data, a client
makes the information available to others; by reading data, the
client receives information from others.
Figure 2.1, “A typical client/server system” illustrates this.
So why is this interesting? So far, this sounds like the
definition of a typical file server. And indeed, the repository
is
a kind of file server, but it's not your
usual breed. What makes the Subversion repository special is
that
it remembers every change
ever written
to it: every change to every file, and even changes to the
directory tree itself, such as the addition, deletion, and
rearrangement of files and directories.
When a client reads data from the repository, it normally
sees only the latest version of the filesystem tree. But the
client also has the ability to view
previous
states of the filesystem. For
example, a client can ask historical questions like, “What
did this directory contain last Wednesday?” or “Who
was the last person to change this file, and what changes did
he make?” These are the sorts of questions that are at
the heart of any version control system:
systems that are designed to record and track changes to data
over time.
