Introducing Bazaar
==================

What is Bazaar?
---------------

Bazaar is a tool for helping people collaborate. It tracks the changes
that you and other people make to a group of files - such as software
source code - to give you snapshots of each stage of their evolution.
Using that information, Bazaar can effortlessly merge your work with
other people's.

Tools like Bazaar are called version control systems (VCS) and have
long been popular with software developers. Bazaar's ease of use,
flexibility and simple setup make it ideal not only for software
developers but also for other groups who work together on files and
documents, such as technical writers, web designers and translators.

This guide takes you through installing Bazaar and how to use it,
whether on your own or with a team of other people. If you're already
familiar with distributed version control and want to dive straight in, 
you may wish to skim this section and jump straight to
`Learning more`_.

A brief history of version control systems
------------------------------------------

Version control tools have been evolving for several decades now. In
simple terms, there have been 4 generations of tools:

 1. file versioning tools, e.g. SCCS, RCS
 2. tree versioning tools - central style, e.g. CVS
 3. tree versioning tools - central style, take two, e.g. Subversion
 4. tree versioning tools - distributed style, e.g. Bazaar.

The design and implementation of Bazaar builds on the lessons learned
from all the previous generations of tools. In particular, Bazaar
cleanly supports both the central and the distributed version
control models so you can change models as it makes sense, without
needing to change tools.

Central vs distributed VCS
--------------------------

Many traditional VCS tools require a central server which provides the
change history or *repository* for a tree of files. To work on the files,
users need to connect to the server and *checkout* the files. This gives
them a directory or *working tree* in which a person can make changes.
To record or *commit* these changes, the user needs access to the central
server and they need to ensure they have merged their work with the latest
version stored before trying to commit. This approach is known as the
centralized model. 

The centralized model has proven useful over time but it can have some notable
drawbacks. Firstly, a centralized VCS requires that one is able to connect
to the server whenever one wants to do version control work. Secondly, the
centralized model tightly links the act of **snapshotting** changes with the act
of **publishing** those changes. This can be good in some circumstances but
it has a negative influence on quality in others.

Distributed VCS tools let users and teams have multiple repositories
rather than just a single central one. In Bazaar's case, the history is
normally kept in the same place as the code that is being version controlled.
This allows the user to commit their changes whenever it makes sense, even
when offline. Network access is only required when publishing changes or
when accessing changes in another location.

In fact, using distributed VCS tools wisely can have advantages well
beyond the obvious one of disconnected operations for developers.
Other advantages include:

 * easier for developers to create experimental branches
 * easier ad-hoc collaboration with peers
 * less time required on mechanical tasks - more time for creativity

 * increased release management flexibility through the use of
   "feature-wide" commits

 * trunk quality and stability can be kept higher, making everyone's
   job less stressful

 * in open source communities:

   * easier for non-core developers to create and maintain changes

   * easier for core developers to work with non-core developers and
     move them into the core

 * in companies, easier to work with distributed and outsourced teams.
   
For a detailed look at the advantages of distributed VCS tools over
centralized VCS tools, see http://bazaar-vcs.org/BzrWhy.


Key features of Bazaar
----------------------

While Bazaar is not the only distributed VCS tool around, it does have some
notable features that make it an excellent choice for many teams and
communities. A summary of these and comparisons with other VCS tools
can be found on the Bazaar Wiki, http://bazaar-vcs.org.

Of the many features, one in particular is worth highlighting:
Bazaar is completely free software written in Python. As a result,
it is easy to contribute improvements. If you wish to get involved,
please see http://bazaar-vcs.org/BzrSupport.


Learning more
-------------

This manual provides an easy to read introduction to Bazaar and how to use
it effectively.  It is recommended that all users read at least the rest of
this chapter as it:

 * explains the core concepts users need to know
 * introduces some popular ways of using Bazaar to collaborate.

Chapters 2-6 provide a closer look at how to use Bazaar to complete
various tasks. It is recommended that most users read these in first-to-last
order shortly after starting to use Bazaar. Chapter 7 and beyond provide
additional information that helps you make the most of Bazaar once the core
functionality is understood. This material can be read when required and in
any order.

If you are already familar with other version control tools,
you may wish to get started quickly by reading the following documents:

 * `Bazaar in five minutes`_ - a mini-tutorial

 * `Bazaar Quick Start Card`_ - a one page summary of commonly used commands.

In addition, the online help and `Bazaar User Reference`_ provide all the
details on the commands and options available.

.. _Bazaar in five minutes: ../mini-tutorial/index.html
.. _Bazaar Quick Start Card: ../quick-reference/quick-start-summary.svg
.. _Bazaar User Reference: ../user-reference/bzr_man.html

We hope you find this manual useful. If you have suggestions on how it
or the rest of Bazaar's documentation can be improved, please contact
us on the mailing list, bazaar@lists.canonical.com.
