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<concept xml:lang="en" id="GUID-4C35C86A-D57F-503B-8E55-5D235E0D6DA0"><title>What is versioning</title><shortdesc>This topic describes the purpose and uses of versioning. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody> <p>Tools and applications use a set of classes to represent the data in the Comms Database. These classes are the container classes, which derive from <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>CMDBElement</apiname></xref> and <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>MMetaDatabase</apiname></xref>. </p> <p>The format of the data does not match the format of the data in the database. The implementation of the CommsDat API maps between the external format and the internal format. </p> <p>Future releases of Symbian OS can change the internal format. The map between the external format and the internal format maintains compatibility for tools and applications if the internal format changes. </p> <p>A new internal format is a new version of the interface. If a new version is created, the older version is deprecated, but Symbian OS maintains the compatibility for a managed period. </p> <p>You specify the version you need when you create a session with the Comms Database. </p> <p>A version is defined by an instance of the <xref href="GUID-1CDD0B97-8B00-3373-9908-512C9BC1CF51.dita"><apiname>TVersion</apiname></xref> class. </p> <p>In practice, changes to versions are extremely rare. The curent version is the same version used when the Comms Database was added to Symbian OS. </p> </conbody></concept>