[Checkins] SVN: zopyx.versioning/trunk/zopyx/versioning/storages/mongodb/README.txt added

[Andreas Jung]

Log message for revision 114201:
  added
  

Changed:
  A   zopyx.versioning/trunk/zopyx/versioning/storages/mongodb/README.txt

-=-
Added: zopyx.versioning/trunk/zopyx/versioning/storages/mongodb/README.txt
===================================================================
--- zopyx.versioning/trunk/zopyx/versioning/storages/mongodb/README.txt	                        (rev 0)
+++ zopyx.versioning/trunk/zopyx/versioning/storages/mongodb/README.txt	2010-07-05 12:23:58 UTC (rev 114201)
@@ -0,0 +1,34 @@
+Database layout of the MongoDB storage
+======================================
+
+We use three collections:
+
+metadata
+--------
+
+The ``metadata`` collections has a row for each versioned object. Each row
+consists of the MongoDB internal ``_id`` field, the ``_oid`` field for storing the
+object id of the versioned object and a counter ``_rev`` for counting the object
+revisions (0...N).
+
+revisions
+---------
+
+The ``revisions`` collections is used to store the versioned data. There is a
+row for each revision of each versioned object. ``_oid`` and ``_rev`` are used
+to identifying objects and their revisions. The ``_metadata`` holds metadata
+about the revision itself. By default it contains only the ``created`` field
+and an optional ``comment`` field. Additional revision specific metadata can be
+added through the store() API method. The real data belong to a particular
+revision is stored as ``_data`` field.
+
+collections
+-----------
+This collection is used for versioning object collections. A versioned object
+collection is described by the ``_oid`` and ``_rev`` of the collection itself
+the list objects belong to the collection.  They are stored under
+``collection_content`` as a sequence of embedded subobjects with fields
+``_oid`` and ``_rev`` representing the state (given by its specific revision)
+for each object of the collection.
+
+