1. A computer readable medium having instructions stored thereon that, when executed by a processor, causes the processor to generate one or more recommended items for a user, the instructions comprising: receiving a target items set for the user, wherein the target items set comprises two or more target items; querying a database of a plurality of related items sets using the target items set, wherein each related items set comprises a plurality of related items; in response to the querying, retrieving one or more similar items sets from the plurality of related item sets, wherein each similar items set is similar to the target items set; and performing a union of the similar items sets to generate the recommended items.