Glossary
========

.. glossary::

  ancestor
    An ancestor is one of any of the revisions that this revision is based on.
    The immediately prior revision has a special name, the
    :term:`parent revision`.

  ancestral parent
    Any branch that has been merged by another branch and then committed
    becomes that branches ancestral parent.

  branch
    a line of development. In the simplest of terms, a branch is the record of
    all the commits that have been done. Every :term:`working tree` has a
    branch, but it may be in a different location. The actual revisions
    produced by the commits are stored in a repository, which is sometimes
    shared with other
    branches.

    A frequent activity done by users within the working tree of a branch is to
    merge another branch. In this way users can share changes between two
    branches -- even if the branch is run by someone else.

    Bazaar's default behavior is to put the repository, branch, and working
    tree all in the same place. This combination is called a standalone tree.
    If there is no tree, it is called a :term:`standalone branch`. If the
    repository is shared with other branches, it is called a repository branch.
    A working tree in a different location from its branch is called a
    checkout.

  branch, bound
    A bound branch is a branch that does not commit a new revision until after
    the revision has been applied to another branch and first.

    A bound branch is a part of a :term:`heavyweight checkout`.

  cherry-pick
    A cherrypick is an operation in which the delta between two revisions is
    applied to a working tree. The process is roughly similiar to generating a
    diff between two revisions and applying it to a working tree.

    A cherrypick is a merge in which a range of revisions are selected and
    merged into a working tree . Performing a limited merge is different than a
    normal merge because normal merges imply all missing revisions should be
    merged. One of the results of cherrypicking is the creation of intransitive
    ancestors, which are revisons that are missing one or more of their
    ancestors.

    A cherrypick in Bazaar is a bit more advanced than the cherrypick with some
    other revision control systems, in that a three way merge is performed
    rather than a strict delta between revisions.

    The downside to cherrypicking is that Bazaar does not track cherrypicked
    revisions, although this feature is firmly on the wish list.

    A common use-case for cherrypicking is the back-porting of fixes from an
    ongoing branch of development to stable release branches.

  checkout
    A checkout is essentially a working tree that is linked to a branch at a
    different location.

    Checkouts also have local branches, which function as a local cache. This
    means that checkouts can be used effectively even with branches that are
    accessed through the Internet. Normal checkouts are sometimes called
    heavyweight checkouts to distinguish them from lightweight checkouts.

    A lightweight checkout is a related construct that lacks the local branch.
    Lightweight checkouts are smaller, but require fast access to the branch,
    such as on a LAN or local hard disk.

    Checkouts provide a location for people to hack on code and commit. Once a
    user commits, the associated branch is updated with a new revision that
    represents the changes for the commit.

  dag
    Directed Acyclic Graph. The graph of revisions where each revision is
    connected to its parent revisions.

  delta
    A delta is defined as the changes between two revisions. Any RCS that has
    revisions typically builds a delta in order to perform a diff

  merge
    Merging is the process of applying all the changes that were introduced in
    one branch into another branch, without applying any changes that are
    already common to both branches. Sometimes a user will not want all of the
    changes. For these cases, a user may instead prefer a cherrypick, which
    gives the user the option to apply only those revisions that are wanted.

    As well as altering the working tree, bzr's merge command will also get all
    of the revisions that a branch has, and add metadata indicating that a
    merge has been performed.

  merge, criss-cross
    A failed type of merge caused by two branches merging each other at the
    same time.

  nuclear launch codes
    Nuclear launch codes are an example of data that has been committed to a
    branch that must be removed at all costs. Imagine if one had access to the
    launch codes for a nuclear warhead, accidentally committed them to a branch
    and then pushed the branch to a public place.

    In real world situations most people do not have access to nuclear
    launchcodes. Users may have data such as passwords, proprietary code and
    other sensitive data. Accidental release of this type of data is
    potentially damaging to the branch owner -- perhaps damaging enough that
    the developer may hope for a nuclear disaster!

    A user dealing with a nuclear launch code problem needs specific data in
    the branch to be exised at all costs and in a rapid manner.

  repository
    A library of revisions for branches.

  revision
    A revision is one state of the code.

    bzr is snapshot based, meaning that conceptually it stores the whole state
    of the tree at each revision. This is in contrast to changeset based, where
    a revision refers to just the changes that were made in that revision. I
    said "conceptually", as internally bzr uses delta compression to reduce the
    amount of data that it stores, and so may only record the changes in a
    revision. However you must always think of a revision as referring to a
    whole snapshot.

    A revision also contains some metadata. In particular it stores the
    committer, and the timestamp when the commit was made, the log message that
    was given, and the nick of the branch on which the commit was made. It also
    stores pointers to the parent revisions, i.e. the revision preceeding it,
    and the tip revisions of any branches that were merged. Lastly it stores a
    number of revision properties, these is extra information that can be
    stored with the revision and is immutable, some uses of them are to store
    the author of the patch if it wasn't the committer (when given using the
    --author option of bzr commit), or to store information about the bugs
    fixed in that revision if using the bug-tracker integration.

    A revision also has a name, referred to as a revision id. This is a
    globally unique identifier for the revision so that it can be referred to
    without ambiguity. This means that two revisions are identical, if, and
    only if, they have the same revision id.

    A revision may also be referred to using a revision number, however this is
    not a globally unique identifier, meaning that revision 14 of your branch
    may not be the same as revision 14 of my branch, even if they are the same
    project. The only way to know if they are the same revision is to compare
    the revision ids. This means that when talking about a revision you must
    either use it's revision id, or also explain which branch you are referring
    to when you specify a revision number.

    Tags point at a revision, and so they may also be used to when referring to
    a commit, but again, two different branches may have the same tag name
    pointing to two different revisions, and so you should also give the branch
    to which you are referring when stating a tag name.

  revision, ancestor
    An ancestor is one of any of the revisions that this revision is based on.
    The immediately prior revision has a special name, the parent revision.

  revision, ghost
    A ghost :term:`revision`, also called a ghost, is a revision that a
    :term:`branch` knows about but does not have.

    Ghost revisions can occur in unusual situations such as the migration of
    branches from foreign revision control systems into Bazaar format.

    Ghost revisions can be scary the first time that a user bumps into them.
    Thankfully though, revision ghosts are just like real ghosts (such as they
    are) in that their discorporeal existence typically causes little, if any,
    harm.

  revision, parent
    The revision that comes immediately prior to this revision.

  shared repository
    A shared repository is similar to the traditional concept of a repository
    in other VCSs like CVS and Subversion. For example, in Subversion you have
    a remote repository, which is where all of the history is stored, and
    locally you don't have any history information, only a checkout of the
    working tree files. Note that "Shared" in this context means shared between
    branches. It *may* be shared between people, but standalone branches
    can also be shared between people.

    In Breezy_ terms, a "Shared Repository" is a location where multiple
    branches can **share** their revision history information. In order to
    support decentralized workflows, it is possible for every branch to
    store its own revision history information. But this is often
    inefficient, since related branches share history, and they might as
    well share the storage as well.

  tag
    A tag is a nickname for a particular :term:`revision`. The typical use is to mark a
    release of the software so you can easily refer to it later.

  working tree
    A working tree is a directory with project files that a user can edit.

    Unlike a normal directory, a working tree is associated with a
    :term:`branch`. The working tree is the space in which commands such as
    commit and revert operate.
