nn - 1 Near-Neighbor Search Applications Matrix Formulation...

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Unformatted text preview: 1 Near-Neighbor Search Applications Matrix Formulation Minhashing 2 Example Problem--- Face Recognition r We have a database of (say) 1 million face images. r We are given a new image and want to find the most similar images in the database. r Represent faces by (relatively) invariant values, e.g., ratio of nose width to eye width. 3 Face Recognition --- (2) r Each image represented by a large number (say 1000) of numerical features. r Problem : given the features of a new face, find those in the DB that are close in at least (say) of the features. 4 Face Recognition --- (3) r M a n y - o n e p r o b l e m : given a new face, see if it is close to any of the 1 million old faces. r a n y - M a n y p r o b l e m : which pairs of the 1 million faces are similar. 5 Simple Solution r Represent each face by a vector of 1000 values and score the comparisons. r Sort-of OK for many-one problem. r Out of the question for the many-many problem (10 6 *10 6 *1000 numerical comparisons). r We can do better ! 6 Multidimensional Indexes Dont Work New face: [6,14,] 0-4 5-9 10-14 . . . Dimension 1 = Surely wed better look here. Maybe look here too, in case of a slight error. But the first dimension could be one of those that is not close. So wed better look everywhere! 7 Another Problem : Entity Resolution r Two sets of 1 million name-address-phone records. r Some pairs, one from each set, represent the same person. r Errors of many kinds : R Typos, missing middle initial, area-code changes, St./Street, Bob/Robert, etc., etc. 8 Entity Resolution --- (2) r Choose a scoring system for how close names are. R Deduct so much for edit distance > 0; so much for missing middle initial, etc. r Similarly score differences in addresses, phone numbers. r Sufficiently high total score -> records represent the same entity. 9 Simple Solution r Compare each pair of records, one from each set. r Score the pair. r Call them the same if the score is sufficiently high. r Unfeasible for 1 million records. r We can do better ! 10 Yet Another Problem : Finding Similar Documents r Given a body of documents, e.g., the Web, find pairs of docs that have a lot of text in common....
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nn - 1 Near-Neighbor Search Applications Matrix Formulation...

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