= Serialize to XML / Deserialize from XML (moin 2.x) =

We need (de-)serialization at quite some places:
 * (complete) wiki backup / restore: data and user items
 * import/export of single items or sets of items (see page packages in moin 1.x)
  * PackagePages
  * system / help page packs (+ i18ned versions)
 * wikisync for inter-wiki transfer of item revisions
 * wiki xmlrpc (v3?)
 * a format usable to write importers / exporters for other wiki engines (markup conversion shall not be part of this feature request)

= Ideas for serialization format =
== Complete dump ==
{{{
<wiki>
 <meta>
 ... (wiki-level metadata) ...
 </meta>
 <items>
  ... (items) ...
 </items>
</wiki>
}}}

== Item serialization (1 complete item) ==
{{{
<item type="user|data" name="...">
 <meta>
 ... (item-level metadata) ...
 </meta>
 <revision revno="0">
  <meta>
  ... (revision-level metadata) ...
  </meta>
  <data>
  ... (revision data) ...
  </data>
 </revision>
 ... (more revisions) ...
</item>
}}}

== Metadata representation ==
{{{
<meta>
 <entry name="key1">value1</entry>
 <entry name="key2">value2</entry>
 ...
</meta>
}}}

== Data representation and dealing with large data ==
As we store arbitrary binary items, stuff can easily get rather big (e.g. if someone attaches a CD or DVD image, maybe even in multiple revisions).

=== Embedding chunked revision data ===
!ElementTree (and also !EmeraldTree) does not seem to support data streaming (i.e. we can't read item data chunk-wise and write it to a ''single'' xml element).

But we can create multiple data-chunk elements, like:
{{{
<data>
 <chunk>... 100kB data ...</chunk>
 <chunk>... 100kB data ...</chunk>
 <chunk>... 42kB data (== the rest)...</chunk>
</data>
}}}

The data inside the chunk could be base64-encoded to support all item mimetypes in the same way.

=== Referring to revision data ===
 * put href: reference to data revision into xml dump (source wiki needs to be reachable to fetch the data later)
 * put file: reference to data revision into xml dump, write revision data to separate files (no access to src wiki needed)

== Integrity checking ==
Data integrity can be checked using the hash we have in the metadata.

== Serializer features ==
 * complete wiki (data and users)
 * sets of (named) items
  * with all revisions
  * just latest revision
  * with some revisions (since timestamp? all revision hashes we do not have yet?)
 * revisions need to be serialized in-order (0,1,2,...)
  * in any case: per item
  * globally in order of timestamp (see "backend.history()" output)?

= See also =
 * http://meta.wikimedia.org/wiki/Help:Export

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CategoryFeatureRequest