“…It is also noticeable that most FSSs developed to date operate on single domain [3,5,11,13,[20][21][22][23][24][25][26][27][28]30,36,39,41,44,46,51], although some experiment with multiple domains [1,40,43,47,48], and a few FSSs attempt open domains search, e.g., for the general web [14,18,50].…”