Fossil

The local state is not versioned and is not synchronized
with the global state.
The local state is not composed of artifacts and is not intended to be enduring.
This document is concerned with global state only.  Local state is only
mentioned here in order to distinguish it from global state.

Each artifact in the repository is named by its SHA1 hash.
No prefixes or meta information is added to an artifact before
its hash is computed.  The name of an artifact in the repository
is exactly the same SHA1 hash that is computed by sha1sum 
on the file as it exists in your source tree.</p>

Some artifacts have a particular format which gives them special
meaning to fossil.  Fossil recognizes:

<ul>

A sample manifest from Fossil itself can be seen
[/artifact/28987096ac | here].

<a name="cluster"></a>
<h2>2.0 Clusters</h2>

A cluster is an artifact that declares the existence of other artifacts.
Clusters are used during repository synchronization to help 
reduce network traffic.  As such, clusters are an optimization and
may be removed from a repository without loss or damage to the
underlying project code.

Clusters follow a syntax that is very similar to manifests.
A Cluster is a line-oriented text file.  Newline characters

collection of artifacts.  Each artifact is named by 
its SHA1 hash encoded in lowercase hexadecimal.
In many contexts, the name can be
abbreviated to a unique prefix.  A five- or six-character
prefix usually suffices to uniquely identify a file.</p></li>

<li><p>Because artifacts are named by their SHA1 hash, all artifacts
are immutable.  Any change to the content of an artifact also 
changes the hash that forms the artifacts name, thus
creating a new artifact.  Both the old original version of the
artifact and the new change are preserved under different names.</p></li>

<li><p>It is theoretically possible for two artifacts with different
content to share the same hash.  But finding two such
artifacts is so incredibly difficult and unlikely that we

<h3>3.13 Unknown Cards</h3>

<p>If either the client or the server sees a card that is not
described above, then it generates an error and aborts.</p>

<h2>4.0 Phantoms And Clusters</h2>

<p>When a repository knows that an artifact exists and knows the ID of
that artifact, but it does not know the artifact content, then it stores that
artifact as a "phantom".  A repository will typically create a phantom when
it receives an igot card for an artifact that it does not hold or when it
receives a file card that references a delta source that it does not
hold.  When a server is generating its reply or when a client is
generating a new request, it will usually send gimme cards for every
phantom that it holds.</p>

<p>A cluster is a special artifact that tells of the existence of other
artifacts.  Any artifact in the repository that follows the syntactic rules
of a cluster is considered a cluster.</p>

<p>A cluster is line oriented.  Each line of a cluster
is a card.  The cards are separated by the newline ("\n") character.
Each card consists of a single character card type, a space, and a
single argument.  No extra whitespace and no trailing or leading
whitespace is allowed.  All cards in the cluster must occur in
strict lexicographical order.</p>

<p>A cluster consists of one or more "M" cards followed by a single
"Z" card.  Each M card holds an argument which is an artifact ID for an
artifact in the repository.  The Z card has a single argument which is the
lower-case hexadecimal representation of the MD5 checksum of all
preceding M cards up to and included the newline character that
occurred just before the Z that starts the Z card.</p>

<p>Any artifact that does not match the specifications of a cluster
exactly is not a cluster.  There must be no extra whitespace in