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The "FS2/Design" page has been changed by brane: http://wiki.apache.org/subversion/FS2/Design?action=diff&rev1=5&rev2=6 ## page was renamed from FS2_Design = The Versioned Filesystem = - Subversion's versioned filesystem is a set of snapshots of the state of a tree of nodes. Changes to the tree are described by ''transactions'', which are a set of mutations of the tree state. Discrete states of the tree are called ''revisions'' and are represented by immutable transactions. Each snapshot (except for the first, which has none and is called ''revision 0'') has exactly one predecessor and at most one immutable successor. Any number of mutable transactions can exist at the same time. The set of revisions is a temporally ordered sequence; the last or ''youngest'' revision is called the ''HEAD''. New revisions are created by ''merging'' the changes described by a mutable transaction with the tree state represented by HEAD and appending the resulting revision to the sequence, creating a new HEAD. + Subversion's versioned filesystem is a temporally ordered sequence of discrete snapshots of the state of a tree of nodes. These immutable snapshots are called ''revisions''. The initial revision (''Revision 0'') contains exactly one node, the ''root directory''. The last, or ''youngest'' revision, is called the ''HEAD''. + + Beside this sequence of immutable revisions, the filesystem can contain an arbitrary number of ''transactions'', which are mutable snapshots that have no successors and whose predecessors (''base revisions'') are immutable. The only way to create a new revision is to ''merge'' the ''tree mutations'' described by a transaction into the HEAD tree and appending the result to the revision sequence, thereby creating a new HEAD (in other words, ''rebase'' the transaction to HEAD and make it immutable). [[attachment:vfs-snapshot-sequence.svg|{{attachment:vfs-snapshot-sequence.png}}]]
