9. A system comprising: a memory comprising instructions executable by one or more processors; and the one or more processors coupled to the memory and operable to execute the instructions, the one or more processors being operable when executing the instructions to: construct a classifier based on a plurality of training keywords, wherein: each training keyword comprises one or more words and has a corresponding training keyword document, and construct the classifier comprises: for each training keyword of the plurality of training keywords, annotate the training keyword with one or more labels of a plurality of labels, each label having a corresponding label document; and for each label annotating the training keyword, determine a correctness of the label; calculate a first index-wise product between a word count vector of the training keyword document corresponding to the training keyword and a word count vector of the label document corresponding to the label; and form a pair of the correctness and the first index-wise product; and train the classifier using one or more pairs of the correctness and the first index-wise product; and for each keyword of a plurality of keywords, the keyword being annotated with one or more labels of the plurality of labels, for each label annotating the keyword, calculate a second index-wise product between a word count vector of the keyword document corresponding to the keyword and a word count vector of the label document corresponding to the label; and predict whether the label annotating the keyword is correct using the classifier with the second index-wise product as an input to the classifier.
13. The system of claim 9 , wherein the one or more processors are further operable when executing the instructions to: group the plurality of keywords into one or more keyword groups based on similarities between the one or more labels annotating each keyword, each keyword group comprising one or more keywords of the plurality of keywords; and form one or more advertising groups from the one or more keyword groups, comprising: form at least one of the one or more advertising groups from each keyword group, each advertising group comprising at least one of the one or more keywords in the keyword group.