22. A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising: identifying, by one or more processors, one or more web pages impressions satisfying a first query criteria, each web page impression being an instance of a previous presentation of a web page, where each web page has one or more attributes and associated values that describe entities that are targeted by the web page and where identifying one or more impressions includes comparing terms of the first query criteria to the one or more attributes and associated values associated of a given web page; identifying, by one or more processors, one or more web pages impressions satisfying a second query criteria including comparing terms of the second query criteria to the one or more attributes and values of a given web page, the first query criteria and the second query criteria being mutually exclusive; storing respective impression IDs associated with the respective one or more web pages satisfying the first query criteria and associated with the respective one or more web pages satisfying the second query criteria; subsequent to storing the respective impression IDs, receiving a query from a client device, the query including the first query criteria and the second query criteria; identifying, by one or more processors, a number of web page impressions satisfying the query as the number of impression IDs associated with both the one or more web pages satisfying the first query criteria and one or more web pages satisfying the second query criteria; and determining that the query received from the client device exceeds a predetermined number of criteria.
22. A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising: identifying, by one or more processors, one or more web pages impressions satisfying a first query criteria, each web page impression being an instance of a previous presentation of a web page, where each web page has one or more attributes and associated values that describe entities that are targeted by the web page and where identifying one or more impressions includes comparing terms of the first query criteria to the one or more attributes and associated values associated of a given web page; identifying, by one or more processors, one or more web pages impressions satisfying a second query criteria including comparing terms of the second query criteria to the one or more attributes and values of a given web page, the first query criteria and the second query criteria being mutually exclusive; storing respective impression IDs associated with the respective one or more web pages satisfying the first query criteria and associated with the respective one or more web pages satisfying the second query criteria; subsequent to storing the respective impression IDs, receiving a query from a client device, the query including the first query criteria and the second query criteria; identifying, by one or more processors, a number of web page impressions satisfying the query as the number of impression IDs associated with both the one or more web pages satisfying the first query criteria and one or more web pages satisfying the second query criteria; and determining that the query received from the client device exceeds a predetermined number of criteria. 23. The medium of claim 22 , further comprising operations of dividing the query into two queries having, respectively, the first query criteria and the second query criteria.