This section is from the "Version Control with Subversion" book, by Ben Collins-Sussman, Brian W. Fitzpatrick and C. Michael Pilato. Also available from Amazon: Version Control with Subversion.
On the client side, the Subversion working copy is where all the action takes place. The bulk of functionality implemented by the client-side libraries exists for the sole purpose of managing working copies—directories full of files and other subdirectories which serve as a sort of local, editable “reflection” of one or more repository locations—and propagating changes to and from the Repository Access layer.
Subversion's working copy library, libsvn_wc, is directly
responsible for managing the data in the working copies. To
accomplish this, the library stores administrative information
about each working copy directory within a special
subdirectory. This subdirectory, named
.svn
, is present in each working copy
directory and contains various other files and directories
which record state and provide a private workspace for
administrative action. For those familiar with CVS, this
.svn
subdirectory is similar in purpose
to the CVS
administrative directories
found in CVS working copies. For more information about the
.svn
administrative area, see the section called “Inside the Working Copy Administration Area”in this chapter.
The Subversion client library, libsvn_client, has the
broadest responsibility; its job is to mingle the
functionality of the working copy library with that of the
Repository Access Layer, and then to provide the highest-level
API to any application that wishes to perform general revision
control actions. For example, the function
svn_client_checkout()
takes a URL as an
argument. It passes this URL to the RA layer and opens an
authenticated session with a particular repository. It then
asks the repository for a certain tree, and sends this tree
into the working copy library, which then writes a full
working copy to disk (.svn
directories
and all).
The client library is designed to be used by any
application. While the Subversion source code includes a
standard command-line client, it should be very easy to write
any number of GUI clients on top of the client library. New
GUIs (or any new client, really) for Subversion need not be
clunky wrappers around the included command-line
client—they have full access via the libsvn_client API
to same functionality, data, and callback mechanisms that the
command-line client uses. In fact, the Subversion source code
tree contains a small C program (which can be found at
tools/examples/minimal_client.c
that
exemplifies how to wield the Subversion API to create a simple
client program