#  Query Type: 7, Cross-delta structured queries (queries performed on changes of several versions (multiple deltas))
#  Query Description : 
#  Retrieve the average number of added News Items from version Vi to version Vi+2.

PREFIX cwork:<http://www.bbc.co.uk/ontologies/creativework/> 

SELECT ((?ViPlus1_news_items_added + ?ViPlus2_news_items_added) / 2 AS ?avg_added_news_items)
WHERE {
{ 
   SELECT (COUNT(*) AS ?ViPlus1_news_items_added )
   WHERE { 
   	GRAPH {{{graphViPlus1}}} { ?creativeWork a cwork:NewsItem } 
   	MINUS { GRAPH {{{graphVi}}} { ?creativeWork a cwork:NewsItem } } }
} . 
{ 
   SELECT (COUNT(*) AS ?ViPlus2_news_items_added)
   WHERE { 
   	GRAPH {{{graphViPlus2}}} { ?creativeWork a cwork:NewsItem } 
   	MINUS { GRAPH {{{graphViPlus1}}} { ?creativeWork a cwork:NewsItem } } }
} . }