1. A computer-implemented method comprising: normalizing a plurality of keywords received from a source, the source being from the group: a search query and a product listing; filtering the normalized plurality of keywords against one or more keyword filtration lists; producing site-specific variants of the filtered plurality of keywords; associating a plurality of levels of dimension data with each of the plurality of keywords, the plurality of levels of dimension data including information indicative of a probability that a keyword of the plurality of keywords belongs to a particular product category in a product category hierarchy, the plurality of levels of dimension data including keyword clustering dimension data, the keyword clustering dimension data including information indicative of a probability that a keyword of the plurality of keywords belongs to a particular keyword cluster of a plurality of pre-defined keyword clusters, the plurality of levels of dimension data including keyword traffic dimension data, the keyword traffic dimension data including information indicative of a probability that a keyword of the plurality of keywords was trafficked by a particular search engine, wherein the probability that a keyword of the plurality of keywords was trafficked by a particular search engine is maintained for each of a plurality of search engines, the keyword traffic dimension data including information indicative of a probability that a keyword of the plurality of keywords will achieve a predicted revenue per click level, the keyword traffic dimension data including information indicative of a value related to confirmed registered users, the keyword traffic dimension data including information indicative of a landing page related to a particular cluster of keywords; defining a time period of measurement for a metric corresponding to the plurality of levels of dimension data; and storing the processed plurality of keywords and dimension data in a keyword database, and selecting at least one keyword from the stored processed plurality of keywords according to the dimension data in the keyword database.