Updated the doc with the idea of OBIDMS release files.

doc/source/formats.rst

@@ -9,6 +9,7 @@ The OBItools3 Data Management System (OBIDMS)
 
 An OBIDMS directory consists of : 
 	* OBIDMS column files
+	* OBIDMS release files
 	* an OBIDMS history file
 
 
@@ -56,12 +57,15 @@ A column of data of the same type.
 Versioning
 ----------
 
-Since OBIDMS column files are read-only, any modification leads to the creation of a new version 
+OBIDMS column files are read-only, and any modification leads to the creation of a new version 
-of the column file.
+of the column file. That means that one column is stored in one file (if there is only one version) 
+or more (if there are several versions), and that there is one file per version. 
 
 The first version of a column file is numbered 1, and each new version increments that 
 number by 1.
 
+The number of the latest version of an OBIDMS column is stored in an `OBIDMS release file <formats.html#obidms-release-files>`_.
+
 
 Mandatory columns
 -----------------
@@ -69,7 +73,22 @@ Mandatory columns
 Some columns must exist in an OBIDMS directory :
 	* sequence identifiers column
 
-	
+
+OBIDMS release files
+====================
+ 
+Each OBIDMS column is associated with an OBIDMS release file that contains the number of the latest
+version of the column. 
+
+File name
+---------
+
+OBIDMS release files are named with the attribute associated to the data contained in the column, and 
+have the extension ``.odr``.
+
+Example : ``count.odr``
+
+
 OBIDMS history file
 ===================