perkeep/website/content/docs/schema/permanode

<h1>Permanodes</h1>

<p>
  Permanodes are how Camlistore models mutable data on top of an
  immutable, content-addressable datastore. The data is modeled using
  nodes with two camliTypes: <tt>permanode</tt> and <tt>claim</tt>.
</p>

<h2 id="permanode">Permanode</h2>
<p>
  A permanode is an anchor from which you build mutable objects.  To
  serve as a reliable (consistently nameable) object, it must have no
  mutable state itself. In fact, a permanode is really just a
  <a href="/gw/doc/json-signing/json-signing.txt">signed</a> random
  number.
</p>
<pre>
{"camliVersion": 1,
 "camliType": "permanode",

 // Required.  Any random string, to force the digest of this
 // node to be unique.  Note that the date in the ASCII-armored
 // GPG JSON signature will already help it be unique, so this
 // doesn't need to be a great random.
 "random": "615e05c68c8411df81a2001b639d041f"

<a href="/gw/doc/json-signing/json-signing.txt">&lt;REQUIRED-JSON-SIGNATURE&gt;</a>}
</pre>

<h2 id="claim">Claim</h2>
<p>
  A claim is any signed JSON schema blob. One common use is modifying
  "attributes" on a permanode. The state of a permanode is the result
  of combining all attribute-modifying claims which reference it, in
  order. Claim nodes look something like this:
</p>
<pre>
{"camliVersion": 1,
 "camliType": "claim",
 "camliSigner": "....",
 "claimDate": "2010-07-10T17:20:03.9212Z", // redundant with data in ascii armored "camliSig",
                                           // but required. more legible. takes precedence over
                                           // any date inferred from camliSig
 "permaNode": "sha1-xxxxxxx",        // what is being modified
 "claimType": "set-attribute",
 "attribute": "camliContent",
 "value": "sha1-yyyyyyy",
 "camliSig": .........}
</pre>
<p>
  All claims must be <a href="/gw/doc/json-signing/json-signing.txt">signed</a>.
<p>
  The anagrammatical property <tt>claimType</tt> defines what the
  claim does, and is one of the following:
</p>
<ul>
  <li>
    <tt>add-attribute</tt>: adds a value to a multi-valued attribute
    (e.g. "tag")
  </li>

  <li>
    <tt>set-attribute</tt>: set a single-valued attribute. equivalent
    to "del-attribute" of "attribute" and then add-attribute.
  </li>

  <li>
    <tt>del-attribute</tt>: deletes all values of "attribute", if no
    "value" given, or just the provided "value" if multi-valued
  </li>

  <li>
    <tt>multi</tt>: atomically do multiple add/set/del from above on
    potentially different permanodes. looks like:
    <pre>
   {"camliVersion": 1,
    "camliType": "claim",
    "claimType": "multi",
    "claimDate": "2013-02-24T17:20:03.9212Z",
    "claims": [
         {"claimType": "set-attribute",
          "permanode": "sha1-xxxxxx",
          "attribute": "foo",
          "value": "fooValue"},
         {"claimType": "add-attribute",
          "permanode": "sha1-yyyyy",
          "attribute": "tag",
          "value": "funny"}
    ],
    "camliSig": .........}
    </pre>
  </li>
</ul>

<h2 id="attributes">Attributes</h2>

<p>
  A permanode can have any attribute you like, but here are the ones
  that currently mean something to Camlistore:
</p>
<ul>
  <li>
    <tt>tag</tt>: a set of zero or more keywords (or phrases) indexed
    completely, for searching by tag. No HTML.
  </li>
  <li>
    <tt>title</tt>: A name given to the permanode. No HTML.
  </li>
  <li>
    <tt>description</tt>: An account of the permanode. It may include but is
    not limited to: an abstract, a table of contents, or a free-text
    account of the resource. No HTML.
  </li>
  <li>
    <tt>camliContent</tt>: A reference to another blob. If a permanode
    has this attribute, it's considered a pointer to its camliContent
    value.
  </li>
  <li>
    <tt>camliMember</tt>: A reference to another permanode. This
    indicates that the referenced permanode is a dynamic set, and
    we're a part of it.
  </li>
  <li>
    <tt>camliPath:*</tt>: camliPath attributes are set on permanodes
    which represent dynamic directories. If a permanode has attributes:
    <pre>
    camliPath:dir2 = $blobref_dir2_permandode
    camliPath:bar.txt = $blobref_bartxt_permanode
    </pre>
    It will appear as a directory containing "dir2" and
    "bar.txt".
    <br>
    These are used by a few things, including the website UI, the
    "publish" code (declaring you want a photo at a URL and then the
    HTTP front end resolving each directory link in
    http://myhostname.com/pics/x/y/x/funny.jpg), and the FUSE
    read/write filesystem code.
  </li>
</ul>