“…, Sun and Lim (2001), Mladenic and Grobelnik (2003), Sun et al (2003Sun et al ( , 2004, Wu et al (2005), Cesa-Bianchi et al (2006a,b), Esuli et al (2008), Jin et al (2008), Punera and Ghosh (2008), Xue et al (2008) and Bennett and Nguyen (2009) LCPN Koller and Sahami (1997), Chakrabarti et al (1998), McCallum et al (1998, Weigend et al (1999), D'Alessio et al (2000), Dumais and Chen (2000), Ruiz and Srinivasan (2002), Tikk and Biró (2003), Tikk et al ( , 2007, Kriegel et al (2004) and Gauch et al (2009) GC Labrou and Finin (1999), Wang et al (1999Wang et al ( , 2001, Dekel et al (2004a), Hofmann (2004, 2007), Rousu et al (2005Rousu et al ( , 2006, Kiritchenko et al (2005Kiritchenko et al ( , 2006, Peng and Choi (2005) Holden and Freitas (2005, 2009), Secker et al (2007, 2010, Costa et al (2008) and Kriegel et al (2004) Acknowledgements The first author is financially supported by CAPES-a Brazilian research-support agency (process number 4871-06-5). We also thank the anonymous reviewers for their insightful feedback on the earlier version of this manuscript.…”