Tomoko Murakami Koichiro Mori Ryohei Orihara Metrics for Evaluating the Serendipity of Recommendation Lists. 40-46 2007 JSAI http://dx.doi.org/10.1007/978-3-540-78197-4_5 conf/jsai/2007 db/conf/jsai/jsai2007.html#MurakamiMO07