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<h3>2.1 Identification Of Artifacts</h3>
<p>A particular version of a particular file is called an "artifact".
Each artifact has a universally unique name which is the
<a href="http://en.wikipedia.org/wiki/SHA">SHA1</a> hash of the content
of that file expressed as 40 characters of lower-case hexadecimal. Such
a hash is referred to as the Universally Unique Identifier or UUID
a hash is referred to as the Artifact Identifier or Artifact ID
for the artifact. The SHA1 algorithm is created with the purpose of
providing a highly forgery-resistent identifier for a file. Given any
file it is simple to find the UUID for that file. But given a
UUID it is computationally intractable to generate a file that will
have that UUID.</p>
file it is simple to find the artifact ID for that file. But given a
artifact ID it is computationally intractable to generate a file that will
have that Artifact ID.</p>
<p>UUIDs look something like this:</p>
<p>Artifact IDs look something like this:</p>
<blockquote><b>
6089f0b563a9db0a6d90682fe47fd7161ff867c8<br>
59712614a1b3ccfd84078a37fa5b606e28434326<br>
19dbf73078be9779edd6a0156195e610f81c94f9<br>
b4104959a67175f02d6b415480be22a239f1f077<br>
997c9d6ae03ad114b2b57f04e9eeef17dcb82788
</b></blockquote>
<p>When referring to an artifact using fossil, you can use a unique
prefix of the UUID that is four characters or longer. This saves
a lot of typing. When displaying UUIDs, fossil will usually only
prefix of the artifact ID that is four characters or longer. This saves
a lot of typing. When displaying artifact IDs, fossil will usually only
show the first 10 digits since that is normally enough to uniquely
identify a file.</p>
<p>Changing (or adding or removing) a single byte in a file results
in a completely different UUID. And since the UUID is the name of
in a completely different artifact ID. And since the artifact ID is the name of
the artifact, making any change to a file results in a new artifact.
In this way, artifacts are immutable.</p>
<p>A repository is really just an unordered collection of
artifacts. New artifacts can be added to the repository, but
existing artifacts can never be removed. Fossil is designed in
such a way that it can be handed a set of artifacts in any
order and it can figure out the relationship between those
artifacts and reconstruct the complete development history of
a software project.</p>
<h3>2.2 Manifests</h3>
<p>At the root of a source tree is a special file called the
"manifest". The manifest is a listing of all other files in
that source tree. The manifest contains the (complete) UUID
that source tree. The manifest contains the (complete) artifact ID
of the file and the name of the file as it appears on disk,
and thus serves as a mapping from UUID to disk name. The UUID
of the manifest is the UUID that identifies a baseline. When
you look at a "timeline" of changes in fossil, the UUID associated
with each check-in or commit is really just the UUID of the
and thus serves as a mapping from artifact ID to disk name. The artifact ID
of the manifest is the identifier for the entire baseline. When
you look at a "timeline" of changes in fossil, the ID associated
with each check-in or commit is really just the artifact ID of the
manifest for that baseline.</p>
<p>Fossil automatically generates a manifest whenever you "commit"
a new baseline. So this is not something that you, the developer,
need to worry with. The format of a manifest is intentionally
designed to be simple to parse, so that if
you want to read and interpret a manifest, either by hand or
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<ul>
<li>A <b>baseline</b> is a set of files arranged
in a hierarchy.</li>
<li>A <b>repository</b> keeps a record of historical baselines.</li>
<li>Repositories share their changes using <b>push</b>, <b>pull</b>,
<b>sync</b>, and <b>clone</b>.</li>
<li>A particular version of a particular file is an <b>artifact</b>
that is identified by a <b>UUID</b>.</li>
that is identified by an <b>artifact ID</b>.</li>
<li>Artifacts tracked by fossil are inherently immutable.</li>
<li>Fossil automatically generates a <b>manifest</b> file that identifies
every artifact in a baseline.</li>
<li>The UUID of the manifest is the UUID of the baseline.</li>
<li>The artifact ID of the manifest is the identifier of the baseline.</li>
</ul>
<h2>3.0 Fossil - The Program</h2>
<p>Fossil is software. The implementation of fossil is in the form
of a single executable named "fossil". To install fossil on your system,
all you have to do is obtain a copy of this one executable file (either
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