Platform Release 12 included a very useful new feature: the ability to send more than one changeset in a single POST to your store.

To generate a batch changeset from 2 versions of an RDF graph, you can use an ARC plugin called Talis_ChangeSetBuilderPlugin.

To use it:

	  $args = array(
			'before' => $before, //can be rdf/xml, turtle, or an ARC simpleIndex array
			'after' => $after,  //can be rdf/xml, turtle, or an ARC simpleIndex array
		);
		$cs = ARC2::getComponent('Talis_ChangeSetBuilderPlugin', $args);
		$cs_response = $store->get_metabox()->apply_versioned_changeset($cs); 

The plugin also relies upon the IndexUtils Plugin. The easiest way to get them all set up is to change to your arc directory and do:

svn co http://n2.talis.com/svn/playground/kwijibo/PHP/arc/plugins/trunk/ plugins