Relational vs Similarity Selection (cont)
Similarity selection is used in contexts where
- cannot define a precise matching condition
- but can identify a notion of (S similar to T)
- requires a measure d of "distance" between tuples
- d=0 is an exact match, d>0 is less accurate match
- result is a list of pairs [ (t1,d1), (t2,d2), ..., (tn,dn) ] (ordered by di)
Uses for similarity matching:
- text or multimedia (image/music) retrieval
- ranked queries in conventional databases
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