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<h2>Sync Process</h2>
<ol>
<li style="margin-bottom: 1em;">Zotero client sends a /login request to the server with a username
and password and, upon successful authentication, gets back a session
key. Z client uses this session key in all subsequent requests until a)
Firefox is restarted, b) the key expires due to inactivity, or c) the
client logs out with a /logout request.</li>
<li style="margin-bottom: 1em;">Zotero sends a /lock request to the server to get an exclusive
session lock, which prevents other clients from syncing at the same
time. This may be adjusted in the future to allow other clients that
haven't made local changes to pull updated data, but for now they'll
just get an error.<br>
</li>
<li style="margin-bottom: 1em;">Zotero finds all objects (items, creators, collections, etc.) that have been added, changed, or deleted since the last time it synced. (The ids of deleted objects are saved by a Zotero.Notifier observer at delete time.)<br>
</li>
<li style="margin-bottom: 1em;">Zotero sends an /updated request with the server timestamp of the
last successful sync. Z server sends back XML of all data updated on
the server since that timestamp. The XML is validated on the server
using RELAX-NG before it's sent to the client.</li>
<li style="margin-bottom: 1em;">
<p>Zotero processes the updated object data from the server and compares it to local data:</p>
<p></p>
<ol style="list-style-type: lower-alpha;">
<li style="margin-top: 1em; margin-bottom: 1em;">If an object has changed only remotely, it is saved/updated/deleted locally.</li>
<li style="margin-bottom: 1em;">If an object has the same primary id (a small integer) as a local
object but a different secondary key (a unique string generated at
object creation time), it is a different object, so the primary id of
the local version is changed to an available id.</li>
<li style="margin-bottom: 1em;">If an object has been modified both locally and remotely, Zotero
displays a conflict resolution window allowing you to choose between
either version and make manual edits to the merged version.</li>
</ol>
</li>
<li style="margin-bottom: 1em;">Zotero converts updated objects into XML and POSTs to /upload. The
uploaded XML is validated on the server using RELAX-NG, and the server
saves the new data, overwriting existing data.</li>
<li style="margin-bottom: 1em;">Zotero sends an /unlock request to the server, freeing other clients to sync.</li>
</ol>
<h2>Additional Details</h2>
<ul>
<li>All data is transferred using HTTPS.</li>
<li>Data is gzipped in both directions to reduce bandwidth and improve sync time.</li>
</ul>

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