diff --git a/rhodecode/lib/vcs/backends/base.py b/rhodecode/lib/vcs/backends/base.py
new file mode 100644
--- /dev/null
+++ b/rhodecode/lib/vcs/backends/base.py
@@ -0,0 +1,911 @@
+# -*- coding: utf-8 -*-
+"""
+    vcs.backends.base
+    ~~~~~~~~~~~~~~~~~
+
+    Base for all available scm backends
+
+    :created_on: Apr 8, 2010
+    :copyright: (c) 2010-2011 by Marcin Kuzminski, Lukasz Balcerzak.
+"""
+
+
+from itertools import chain
+from rhodecode.lib.vcs.utils import author_name, author_email
+from rhodecode.lib.vcs.utils.lazy import LazyProperty
+from rhodecode.lib.vcs.utils.helpers import get_dict_for_attrs
+from rhodecode.lib.vcs.conf import settings
+
+from rhodecode.lib.vcs.exceptions import ChangesetError, EmptyRepositoryError, \
+    NodeAlreadyAddedError, NodeAlreadyChangedError, NodeAlreadyExistsError, \
+    NodeAlreadyRemovedError, NodeDoesNotExistError, NodeNotChangedError, \
+    RepositoryError
+
+
+class BaseRepository(object):
+    """
+    Base Repository for final backends
+
+    **Attributes**
+
+        ``DEFAULT_BRANCH_NAME``
+            name of default branch (i.e. "trunk" for svn, "master" for git etc.
+
+        ``scm``
+            alias of scm, i.e. *git* or *hg*
+
+        ``repo``
+            object from external api
+
+        ``revisions``
+            list of all available revisions' ids, in ascending order
+
+        ``changesets``
+            storage dict caching returned changesets
+
+        ``path``
+            absolute path to the repository
+
+        ``branches``
+            branches as list of changesets
+
+        ``tags``
+            tags as list of changesets
+    """
+    scm = None
+    DEFAULT_BRANCH_NAME = None
+    EMPTY_CHANGESET = '0' * 40
+
+    def __init__(self, repo_path, create=False, **kwargs):
+        """
+        Initializes repository. Raises RepositoryError if repository could
+        not be find at the given ``repo_path`` or directory at ``repo_path``
+        exists and ``create`` is set to True.
+
+        :param repo_path: local path of the repository
+        :param create=False: if set to True, would try to craete repository.
+        :param src_url=None: if set, should be proper url from which repository
+          would be cloned; requires ``create`` parameter to be set to True -
+          raises RepositoryError if src_url is set and create evaluates to
+          False
+        """
+        raise NotImplementedError
+
+    def __str__(self):
+        return '<%s at %s>' % (self.__class__.__name__, self.path)
+
+    def __repr__(self):
+        return self.__str__()
+
+    def __len__(self):
+        return self.count()
+
+    @LazyProperty
+    def alias(self):
+        for k, v in settings.BACKENDS.items():
+            if v.split('.')[-1] == str(self.__class__.__name__):
+                return k
+
+    @LazyProperty
+    def name(self):
+        raise NotImplementedError
+
+    @LazyProperty
+    def owner(self):
+        raise NotImplementedError
+
+    @LazyProperty
+    def description(self):
+        raise NotImplementedError
+
+    @LazyProperty
+    def size(self):
+        """
+        Returns combined size in bytes for all repository files
+        """
+
+        size = 0
+        try:
+            tip = self.get_changeset()
+            for topnode, dirs, files in tip.walk('/'):
+                for f in files:
+                    size += tip.get_file_size(f.path)
+                for dir in dirs:
+                    for f in files:
+                        size += tip.get_file_size(f.path)
+
+        except RepositoryError, e:
+            pass
+        return size
+
+    def is_valid(self):
+        """
+        Validates repository.
+        """
+        raise NotImplementedError
+
+    def get_last_change(self):
+        self.get_changesets()
+
+    #==========================================================================
+    # CHANGESETS
+    #==========================================================================
+
+    def get_changeset(self, revision=None):
+        """
+        Returns instance of ``Changeset`` class. If ``revision`` is None, most
+        recent changeset is returned.
+
+        :raises ``EmptyRepositoryError``: if there are no revisions
+        """
+        raise NotImplementedError
+
+    def __iter__(self):
+        """
+        Allows Repository objects to be iterated.
+
+        *Requires* implementation of ``__getitem__`` method.
+        """
+        for revision in self.revisions:
+            yield self.get_changeset(revision)
+
+    def get_changesets(self, start=None, end=None, start_date=None,
+                       end_date=None, branch_name=None, reverse=False):
+        """
+        Returns iterator of ``MercurialChangeset`` objects from start to end
+        not inclusive This should behave just like a list, ie. end is not
+        inclusive
+
+        :param start: None or str
+        :param end: None or str
+        :param start_date:
+        :param end_date:
+        :param branch_name:
+        :param reversed:
+        """
+        raise NotImplementedError
+
+    def __getslice__(self, i, j):
+        """
+        Returns a iterator of sliced repository
+        """
+        for rev in self.revisions[i:j]:
+            yield self.get_changeset(rev)
+
+    def __getitem__(self, key):
+        return self.get_changeset(key)
+
+    def count(self):
+        return len(self.revisions)
+
+    def tag(self, name, user, revision=None, message=None, date=None, **opts):
+        """
+        Creates and returns a tag for the given ``revision``.
+
+        :param name: name for new tag
+        :param user: full username, i.e.: "Joe Doe <joe.doe@example.com>"
+        :param revision: changeset id for which new tag would be created
+        :param message: message of the tag's commit
+        :param date: date of tag's commit
+
+        :raises TagAlreadyExistError: if tag with same name already exists
+        """
+        raise NotImplementedError
+
+    def remove_tag(self, name, user, message=None, date=None):
+        """
+        Removes tag with the given ``name``.
+
+        :param name: name of the tag to be removed
+        :param user: full username, i.e.: "Joe Doe <joe.doe@example.com>"
+        :param message: message of the tag's removal commit
+        :param date: date of tag's removal commit
+
+        :raises TagDoesNotExistError: if tag with given name does not exists
+        """
+        raise NotImplementedError
+
+    def get_diff(self, rev1, rev2, path=None, ignore_whitespace=False,
+            context=3):
+        """
+        Returns (git like) *diff*, as plain text. Shows changes introduced by
+        ``rev2`` since ``rev1``.
+
+        :param rev1: Entry point from which diff is shown. Can be
+          ``self.EMPTY_CHANGESET`` - in this case, patch showing all
+          the changes since empty state of the repository until ``rev2``
+        :param rev2: Until which revision changes should be shown.
+        :param ignore_whitespace: If set to ``True``, would not show whitespace
+          changes. Defaults to ``False``.
+        :param context: How many lines before/after changed lines should be
+          shown. Defaults to ``3``.
+        """
+        raise NotImplementedError
+
+    # ========== #
+    # COMMIT API #
+    # ========== #
+
+    @LazyProperty
+    def in_memory_changeset(self):
+        """
+        Returns ``InMemoryChangeset`` object for this repository.
+        """
+        raise NotImplementedError
+
+    def add(self, filenode, **kwargs):
+        """
+        Commit api function that will add given ``FileNode`` into this
+        repository.
+
+        :raises ``NodeAlreadyExistsError``: if there is a file with same path
+          already in repository
+        :raises ``NodeAlreadyAddedError``: if given node is already marked as
+          *added*
+        """
+        raise NotImplementedError
+
+    def remove(self, filenode, **kwargs):
+        """
+        Commit api function that will remove given ``FileNode`` into this
+        repository.
+
+        :raises ``EmptyRepositoryError``: if there are no changesets yet
+        :raises ``NodeDoesNotExistError``: if there is no file with given path
+        """
+        raise NotImplementedError
+
+    def commit(self, message, **kwargs):
+        """
+        Persists current changes made on this repository and returns newly
+        created changeset.
+
+        :raises ``NothingChangedError``: if no changes has been made
+        """
+        raise NotImplementedError
+
+    def get_state(self):
+        """
+        Returns dictionary with ``added``, ``changed`` and ``removed`` lists
+        containing ``FileNode`` objects.
+        """
+        raise NotImplementedError
+
+    def get_config_value(self, section, name, config_file=None):
+        """
+        Returns configuration value for a given [``section``] and ``name``.
+
+        :param section: Section we want to retrieve value from
+        :param name: Name of configuration we want to retrieve
+        :param config_file: A path to file which should be used to retrieve
+          configuration from (might also be a list of file paths)
+        """
+        raise NotImplementedError
+
+    def get_user_name(self, config_file=None):
+        """
+        Returns user's name from global configuration file.
+
+        :param config_file: A path to file which should be used to retrieve
+          configuration from (might also be a list of file paths)
+        """
+        raise NotImplementedError
+
+    def get_user_email(self, config_file=None):
+        """
+        Returns user's email from global configuration file.
+
+        :param config_file: A path to file which should be used to retrieve
+          configuration from (might also be a list of file paths)
+        """
+        raise NotImplementedError
+
+    # =========== #
+    # WORKDIR API #
+    # =========== #
+
+    @LazyProperty
+    def workdir(self):
+        """
+        Returns ``Workdir`` instance for this repository.
+        """
+        raise NotImplementedError
+
+
+class BaseChangeset(object):
+    """
+    Each backend should implement it's changeset representation.
+
+    **Attributes**
+
+        ``repository``
+            repository object within which changeset exists
+
+        ``id``
+            may be ``raw_id`` or i.e. for mercurial's tip just ``tip``
+
+        ``raw_id``
+            raw changeset representation (i.e. full 40 length sha for git
+            backend)
+
+        ``short_id``
+            shortened (if apply) version of ``raw_id``; it would be simple
+            shortcut for ``raw_id[:12]`` for git/mercurial backends or same
+            as ``raw_id`` for subversion
+
+        ``revision``
+            revision number as integer
+
+        ``files``
+            list of ``FileNode`` (``Node`` with NodeKind.FILE) objects
+
+        ``dirs``
+            list of ``DirNode`` (``Node`` with NodeKind.DIR) objects
+
+        ``nodes``
+            combined list of ``Node`` objects
+
+        ``author``
+            author of the changeset, as unicode
+
+        ``message``
+            message of the changeset, as unicode
+
+        ``parents``
+            list of parent changesets
+
+        ``last``
+            ``True`` if this is last changeset in repository, ``False``
+            otherwise; trying to access this attribute while there is no
+            changesets would raise ``EmptyRepositoryError``
+    """
+    def __str__(self):
+        return '<%s at %s:%s>' % (self.__class__.__name__, self.revision,
+            self.short_id)
+
+    def __repr__(self):
+        return self.__str__()
+
+    def __unicode__(self):
+        return u'%s:%s' % (self.revision, self.short_id)
+
+    def __eq__(self, other):
+        return self.raw_id == other.raw_id
+
+    @LazyProperty
+    def last(self):
+        if self.repository is None:
+            raise ChangesetError("Cannot check if it's most recent revision")
+        return self.raw_id == self.repository.revisions[-1]
+
+    @LazyProperty
+    def parents(self):
+        """
+        Returns list of parents changesets.
+        """
+        raise NotImplementedError
+
+    @LazyProperty
+    def id(self):
+        """
+        Returns string identifying this changeset.
+        """
+        raise NotImplementedError
+
+    @LazyProperty
+    def raw_id(self):
+        """
+        Returns raw string identifying this changeset.
+        """
+        raise NotImplementedError
+
+    @LazyProperty
+    def short_id(self):
+        """
+        Returns shortened version of ``raw_id`` attribute, as string,
+        identifying this changeset, useful for web representation.
+        """
+        raise NotImplementedError
+
+    @LazyProperty
+    def revision(self):
+        """
+        Returns integer identifying this changeset.
+
+        """
+        raise NotImplementedError
+
+    @LazyProperty
+    def author(self):
+        """
+        Returns Author for given commit
+        """
+
+        raise NotImplementedError
+
+    @LazyProperty
+    def author_name(self):
+        """
+        Returns Author name for given commit
+        """
+
+        return author_name(self.author)
+
+    @LazyProperty
+    def author_email(self):
+        """
+        Returns Author email address for given commit
+        """
+
+        return author_email(self.author)
+
+    def get_file_mode(self, path):
+        """
+        Returns stat mode of the file at the given ``path``.
+        """
+        raise NotImplementedError
+
+    def get_file_content(self, path):
+        """
+        Returns content of the file at the given ``path``.
+        """
+        raise NotImplementedError
+
+    def get_file_size(self, path):
+        """
+        Returns size of the file at the given ``path``.
+        """
+        raise NotImplementedError
+
+    def get_file_changeset(self, path):
+        """
+        Returns last commit of the file at the given ``path``.
+        """
+        raise NotImplementedError
+
+    def get_file_history(self, path):
+        """
+        Returns history of file as reversed list of ``Changeset`` objects for
+        which file at given ``path`` has been modified.
+        """
+        raise NotImplementedError
+
+    def get_nodes(self, path):
+        """
+        Returns combined ``DirNode`` and ``FileNode`` objects list representing
+        state of changeset at the given ``path``.
+
+        :raises ``ChangesetError``: if node at the given ``path`` is not
+          instance of ``DirNode``
+        """
+        raise NotImplementedError
+
+    def get_node(self, path):
+        """
+        Returns ``Node`` object from the given ``path``.
+
+        :raises ``NodeDoesNotExistError``: if there is no node at the given
+          ``path``
+        """
+        raise NotImplementedError
+
+    def fill_archive(self, stream=None, kind='tgz', prefix=None):
+        """
+        Fills up given stream.
+
+        :param stream: file like object.
+        :param kind: one of following: ``zip``, ``tar``, ``tgz``
+            or ``tbz2``. Default: ``tgz``.
+        :param prefix: name of root directory in archive.
+            Default is repository name and changeset's raw_id joined with dash.
+
+            repo-tip.<kind>
+        """
+
+        raise NotImplementedError
+
+    def get_chunked_archive(self, **kwargs):
+        """
+        Returns iterable archive. Tiny wrapper around ``fill_archive`` method.
+
+        :param chunk_size: extra parameter which controls size of returned
+            chunks. Default:8k.
+        """
+
+        chunk_size = kwargs.pop('chunk_size', 8192)
+        stream = kwargs.get('stream')
+        self.fill_archive(**kwargs)
+        while True:
+            data = stream.read(chunk_size)
+            if not data:
+                break
+            yield data
+
+    @LazyProperty
+    def root(self):
+        """
+        Returns ``RootNode`` object for this changeset.
+        """
+        return self.get_node('')
+
+    def next(self, branch=None):
+        """
+        Returns next changeset from current, if branch is gives it will return
+        next changeset belonging to this branch
+
+        :param branch: show changesets within the given named branch
+        """
+        raise NotImplementedError
+
+    def prev(self, branch=None):
+        """
+        Returns previous changeset from current, if branch is gives it will
+        return previous changeset belonging to this branch
+
+        :param branch: show changesets within the given named branch
+        """
+        raise NotImplementedError
+
+    @LazyProperty
+    def added(self):
+        """
+        Returns list of added ``FileNode`` objects.
+        """
+        raise NotImplementedError
+
+    @LazyProperty
+    def changed(self):
+        """
+        Returns list of modified ``FileNode`` objects.
+        """
+        raise NotImplementedError
+
+    @LazyProperty
+    def removed(self):
+        """
+        Returns list of removed ``FileNode`` objects.
+        """
+        raise NotImplementedError
+
+    @LazyProperty
+    def size(self):
+        """
+        Returns total number of bytes from contents of all filenodes.
+        """
+        return sum((node.size for node in self.get_filenodes_generator()))
+
+    def walk(self, topurl=''):
+        """
+        Similar to os.walk method. Insted of filesystem it walks through
+        changeset starting at given ``topurl``.  Returns generator of tuples
+        (topnode, dirnodes, filenodes).
+        """
+        topnode = self.get_node(topurl)
+        yield (topnode, topnode.dirs, topnode.files)
+        for dirnode in topnode.dirs:
+            for tup in self.walk(dirnode.path):
+                yield tup
+
+    def get_filenodes_generator(self):
+        """
+        Returns generator that yields *all* file nodes.
+        """
+        for topnode, dirs, files in self.walk():
+            for node in files:
+                yield node
+
+    def as_dict(self):
+        """
+        Returns dictionary with changeset's attributes and their values.
+        """
+        data = get_dict_for_attrs(self, ['id', 'raw_id', 'short_id',
+            'revision', 'date', 'message'])
+        data['author'] = {'name': self.author_name, 'email': self.author_email}
+        data['added'] = [node.path for node in self.added]
+        data['changed'] = [node.path for node in self.changed]
+        data['removed'] = [node.path for node in self.removed]
+        return data
+
+
+class BaseWorkdir(object):
+    """
+    Working directory representation of single repository.
+
+    :attribute: repository: repository object of working directory
+    """
+
+    def __init__(self, repository):
+        self.repository = repository
+
+    def get_branch(self):
+        """
+        Returns name of current branch.
+        """
+        raise NotImplementedError
+
+    def get_changeset(self):
+        """
+        Returns current changeset.
+        """
+        raise NotImplementedError
+
+    def get_added(self):
+        """
+        Returns list of ``FileNode`` objects marked as *new* in working
+        directory.
+        """
+        raise NotImplementedError
+
+    def get_changed(self):
+        """
+        Returns list of ``FileNode`` objects *changed* in working directory.
+        """
+        raise NotImplementedError
+
+    def get_removed(self):
+        """
+        Returns list of ``RemovedFileNode`` objects marked as *removed* in
+        working directory.
+        """
+        raise NotImplementedError
+
+    def get_untracked(self):
+        """
+        Returns list of ``FileNode`` objects which are present within working
+        directory however are not tracked by repository.
+        """
+        raise NotImplementedError
+
+    def get_status(self):
+        """
+        Returns dict with ``added``, ``changed``, ``removed`` and ``untracked``
+        lists.
+        """
+        raise NotImplementedError
+
+    def commit(self, message, **kwargs):
+        """
+        Commits local (from working directory) changes and returns newly
+        created
+        ``Changeset``. Updates repository's ``revisions`` list.
+
+        :raises ``CommitError``: if any error occurs while committing
+        """
+        raise NotImplementedError
+
+    def update(self, revision=None):
+        """
+        Fetches content of the given revision and populates it within working
+        directory.
+        """
+        raise NotImplementedError
+
+    def checkout_branch(self, branch=None):
+        """
+        Checks out ``branch`` or the backend's default branch.
+
+        Raises ``BranchDoesNotExistError`` if the branch does not exist.
+        """
+        raise NotImplementedError
+
+
+class BaseInMemoryChangeset(object):
+    """
+    Represents differences between repository's state (most recent head) and
+    changes made *in place*.
+
+    **Attributes**
+
+        ``repository``
+            repository object for this in-memory-changeset
+
+        ``added``
+            list of ``FileNode`` objects marked as *added*
+
+        ``changed``
+            list of ``FileNode`` objects marked as *changed*
+
+        ``removed``
+            list of ``FileNode`` or ``RemovedFileNode`` objects marked to be
+            *removed*
+
+        ``parents``
+            list of ``Changeset`` representing parents of in-memory changeset.
+            Should always be 2-element sequence.
+
+    """
+
+    def __init__(self, repository):
+        self.repository = repository
+        self.added = []
+        self.changed = []
+        self.removed = []
+        self.parents = []
+
+    def add(self, *filenodes):
+        """
+        Marks given ``FileNode`` objects as *to be committed*.
+
+        :raises ``NodeAlreadyExistsError``: if node with same path exists at
+          latest changeset
+        :raises ``NodeAlreadyAddedError``: if node with same path is already
+          marked as *added*
+        """
+        # Check if not already marked as *added* first
+        for node in filenodes:
+            if node.path in (n.path for n in self.added):
+                raise NodeAlreadyAddedError("Such FileNode %s is already "
+                    "marked for addition" % node.path)
+        for node in filenodes:
+            self.added.append(node)
+
+    def change(self, *filenodes):
+        """
+        Marks given ``FileNode`` objects to be *changed* in next commit.
+
+        :raises ``EmptyRepositoryError``: if there are no changesets yet
+        :raises ``NodeAlreadyExistsError``: if node with same path is already
+          marked to be *changed*
+        :raises ``NodeAlreadyRemovedError``: if node with same path is already
+          marked to be *removed*
+        :raises ``NodeDoesNotExistError``: if node doesn't exist in latest
+          changeset
+        :raises ``NodeNotChangedError``: if node hasn't really be changed
+        """
+        for node in filenodes:
+            if node.path in (n.path for n in self.removed):
+                raise NodeAlreadyRemovedError("Node at %s is already marked "
+                    "as removed" % node.path)
+        try:
+            self.repository.get_changeset()
+        except EmptyRepositoryError:
+            raise EmptyRepositoryError("Nothing to change - try to *add* new "
+                "nodes rather than changing them")
+        for node in filenodes:
+            if node.path in (n.path for n in self.changed):
+                raise NodeAlreadyChangedError("Node at '%s' is already "
+                    "marked as changed" % node.path)
+            self.changed.append(node)
+
+    def remove(self, *filenodes):
+        """
+        Marks given ``FileNode`` (or ``RemovedFileNode``) objects to be
+        *removed* in next commit.
+
+        :raises ``NodeAlreadyRemovedError``: if node has been already marked to
+          be *removed*
+        :raises ``NodeAlreadyChangedError``: if node has been already marked to
+          be *changed*
+        """
+        for node in filenodes:
+            if node.path in (n.path for n in self.removed):
+                raise NodeAlreadyRemovedError("Node is already marked to "
+                    "for removal at %s" % node.path)
+            if node.path in (n.path for n in self.changed):
+                raise NodeAlreadyChangedError("Node is already marked to "
+                    "be changed at %s" % node.path)
+            # We only mark node as *removed* - real removal is done by
+            # commit method
+            self.removed.append(node)
+
+    def reset(self):
+        """
+        Resets this instance to initial state (cleans ``added``, ``changed``
+        and ``removed`` lists).
+        """
+        self.added = []
+        self.changed = []
+        self.removed = []
+        self.parents = []
+
+    def get_ipaths(self):
+        """
+        Returns generator of paths from nodes marked as added, changed or
+        removed.
+        """
+        for node in chain(self.added, self.changed, self.removed):
+            yield node.path
+
+    def get_paths(self):
+        """
+        Returns list of paths from nodes marked as added, changed or removed.
+        """
+        return list(self.get_ipaths())
+
+    def check_integrity(self, parents=None):
+        """
+        Checks in-memory changeset's integrity. Also, sets parents if not
+        already set.
+
+        :raises CommitError: if any error occurs (i.e.
+          ``NodeDoesNotExistError``).
+        """
+        if not self.parents:
+            parents = parents or []
+            if len(parents) == 0:
+                try:
+                    parents = [self.repository.get_changeset(), None]
+                except EmptyRepositoryError:
+                    parents = [None, None]
+            elif len(parents) == 1:
+                parents += [None]
+            self.parents = parents
+
+        # Local parents, only if not None
+        parents = [p for p in self.parents if p]
+
+        # Check nodes marked as added
+        for p in parents:
+            for node in self.added:
+                try:
+                    p.get_node(node.path)
+                except NodeDoesNotExistError:
+                    pass
+                else:
+                    raise NodeAlreadyExistsError("Node at %s already exists "
+                        "at %s" % (node.path, p))
+
+        # Check nodes marked as changed
+        missing = set(self.changed)
+        not_changed = set(self.changed)
+        if self.changed and not parents:
+            raise NodeDoesNotExistError(str(self.changed[0].path))
+        for p in parents:
+            for node in self.changed:
+                try:
+                    old = p.get_node(node.path)
+                    missing.remove(node)
+                    if old.content != node.content:
+                        not_changed.remove(node)
+                except NodeDoesNotExistError:
+                    pass
+        if self.changed and missing:
+            raise NodeDoesNotExistError("Node at %s is missing "
+                "(parents: %s)" % (node.path, parents))
+
+        if self.changed and not_changed:
+            raise NodeNotChangedError("Node at %s wasn't actually changed "
+                "since parents' changesets: %s" % (not_changed.pop().path,
+                    parents)
+            )
+
+        # Check nodes marked as removed
+        if self.removed and not parents:
+            raise NodeDoesNotExistError("Cannot remove node at %s as there "
+                "were no parents specified" % self.removed[0].path)
+        really_removed = set()
+        for p in parents:
+            for node in self.removed:
+                try:
+                    p.get_node(node.path)
+                    really_removed.add(node)
+                except ChangesetError:
+                    pass
+        not_removed = set(self.removed) - really_removed
+        if not_removed:
+            raise NodeDoesNotExistError("Cannot remove node at %s from "
+                "following parents: %s" % (not_removed[0], parents))
+
+    def commit(self, message, author, parents=None, branch=None, date=None,
+            **kwargs):
+        """
+        Performs in-memory commit (doesn't check workdir in any way) and
+        returns newly created ``Changeset``. Updates repository's
+        ``revisions``.
+
+        .. note::
+            While overriding this method each backend's should call
+            ``self.check_integrity(parents)`` in the first place.
+
+        :param message: message of the commit
+        :param author: full username, i.e. "Joe Doe <joe.doe@example.com>"
+        :param parents: single parent or sequence of parents from which commit
+          would be derieved
+        :param date: ``datetime.datetime`` instance. Defaults to
+          ``datetime.datetime.now()``.
+        :param branch: branch name, as string. If none given, default backend's
+          branch would be used.
+
+        :raises ``CommitError``: if any error occurs while committing
+        """
+        raise NotImplementedError