1. A computer-implemented method for training a composite similarity function to identify when two records refer to a common underlying subject, comprising: at a computer comprising memory and one or more processors: applying the composite similarity function ƒ*(R 1 ,R 2 ) to pairs of training records, wherein application of the composite similarity function ƒ*(R 1 ,R 2 ) provides a number that can be used to indicate whether two records relate to a common underlying subject, and wherein the composite similarity function ƒ*(R 1 ,R 2 ) is a transform of a weighted linear combination of basis similarity functions: f * ⁡ ( R 1 , R 2 ) = f transform ⁡ [ ∑ i = 1 K ⁢ ⁢ α i ⁢ f i ⁡ ( R 1 , R 2 ) ] wherein ƒ*(R 1 ,R 2 ) is the composite similarity function, wherein the composite similarity function is configured to provide a composite similarity number that is used to indicate whether two records relate to the common underlying subject, and wherein the composite similarity number is adapted to facilitate identification and display of records for the common underlying subject, which is selected from the group consisting of a product a seller, a person and a reference, R 1 and R 2 are two records, ƒ transform [ ] is a transform function, ƒ i (R 1 ,R 2 ) are respective basis similarity functions, and α i are respective weights for respective basis similarity functions; and using an averaged perceptron algorithm to modify the respective weights α i in the weighted linear combination ∑ i = 1 K ⁢ ⁢ α i ⁢ f i ⁡ ( R 1 , R 2 ) .