“…In order to provide approximate answers, these systems are based on consolidated methodologies such as summary tables (Gupta & Quaas, 1995;Huang et al, 2014), sampling (Acharya et al, 1999a;Acharya et al, 1999b;Rösch & Lehner, 2009;Gibbons et al, 1998), histograms (Poosala et al, 1999;Chen & Dobra, 2013;Cormode et al, 2009;Iqbal et al, 2013), wavelets (Chakrabarti et al 2001;Guha et al, 2008), orthonormal series (Lefons et al, 1995;Yan et al, 2007), probabilistic models (Mannila & Smyth, 2000;Missaoui et al, 2007), and clustering (Shanmugasundaram et al, 1999).…”