Signature retrieval and matching for media monitoring

1. An apparatus comprising:

a query processor to obtain a first hash key, first qualifier data and first value data associated with the first hash key in response to a first query of a first table, the first value data including a second hash key and a third hash key both representative of a first reference media, the second hash key preceding the first hash key in time and the third hash key following the first hash key in time;

a candidate qualifier to use the first value data to prequalify the first hash key as a candidate for subsequent signature processing associated with a first site signature, the candidate qualifier to:

determine prequalification of the first hash key is successful in response to a determination that the second hash key matches a second site signature preceding the first site signature in time and that the third hash key matches a third site signature following the first site signature in time; and

determine the prequalification of the first hash key is unsuccessful in response to a determination that at least one of the second hash key fails to match the second site signature or the third hash key fails to match the third site signature.

2. The apparatus of claim 1 , wherein the query processor is to perform the first query of the first table based on a hash corresponding to the first site signature, the first site signature obtained from a monitored site.

3. The apparatus of claim 1 , wherein the first table includes hash keys corresponding to respective reference signatures, and the first qualifier data is descriptive of a reference signature corresponding to the first hash key.

4. The apparatus of claim 3 , wherein the query processor is a first query processor, and further including a second query processor to perform a second query of a second table based on the first qualifier data obtained from the first query of the first table, the second query to obtain, from the second table, a plurality of blocks of reference signatures, the second table different than the first table.

5. The apparatus of claim 4 , wherein the first qualifier data includes a first timestamp associated with a first block of reference signatures including the reference signature, the first qualifier data also including first media identification data identifying first reference media represented by the reference signature.

6. The apparatus of claim 5 , further including a crediting facility to credit media, monitored at a monitored site, as corresponding to the first reference media represented by the reference signature when the prequalification of the first hash key is successful.

7. A non-transitory computer readable medium comprising computer readable instructions which, when execute, cause at least one processor to at least:

obtain a first hash key, first qualifier data and first value data associated with the first hash key in response to a first query of a first table, the first value data including a second hash key and a third hash key both representative of a first reference media, the second hash key preceding the first hash key in time and the third hash key following the first hash key in time;

determine prequalification of the first hash key as a candidate for subsequent signature processing associated with a first site signature is successful in response to a determination that the second hash key matches a second site signature preceding the first site signature in time and that the third hash key matches a third site signature following the first site signature in time; and

determine the prequalification of the first hash key is unsuccessful in response to a determination that at least one of the second hash key fails to match the second site signature or the third hash key fails to match the third site signature.

8. The non-transitory computer readable medium of claim 7 , wherein the instructions cause the at least one processor to perform the first query of the first table based on a hash corresponding to the first site signature, the first site signature obtained from a monitored site.

9. The non-transitory computer readable medium of claim 7 , wherein the first table includes hash keys corresponding to respective reference signatures, and the first qualifier data is descriptive of a reference signature corresponding to the first hash key.

10. The non-transitory computer readable medium of claim 9 , wherein the instructions cause the at least one processor to perform a second query of a second table based on the first qualifier data obtained from the first query of the first table, the second query to obtain, from the second table, a plurality of blocks of reference signatures, the second table different than the first table.

11. The non-transitory computer readable medium of claim 10 , wherein the first qualifier data includes a first timestamp associated with a first block of reference signatures including the reference signature, the first qualifier data also including first media identification data identifying first reference media represented by the reference signature.

12. The non-transitory computer readable medium of claim 11 , wherein the instructions cause the at least one processor to credit media, monitored at a monitored site, as corresponding to the first reference media represented by the reference signature when the prequalification of the first hash key is successful.

13. A method comprising:

obtaining a first hash key, first qualifier data and first value data associated with the first hash key in response to a first query of a first table, the first value data including a second hash key and a third hash key both representative of a first reference media, the second hash key preceding the first hash key in time and the third hash key following the first hash key in time;

determining, by executing an instruction with at least one processor, prequalification of the first hash key as a candidate for subsequent signature processing associated with a first site signature is successful in response to a determination that the second hash key matches a second site signature preceding a first site signature in time and that the third hash key matches a third site signature following the first site signature in time; and

determining, by executing an instruction with the at least one processor, the prequalification of the first hash key is unsuccessful in response to a determination that at least one of the second hash key fails to match the second site signature or the third hash key fails to match the third site signature.

14. The method of claim 13 , further including performing the first query of the first table based on a hash corresponding to the first site signature, the first site signature obtained from a monitored site.

15. The method of claim 13 , wherein the first table includes hash keys corresponding to respective reference signatures, and the first qualifier data is descriptive of a reference signature corresponding to the first hash key.

16. The method of claim 15 , further including performing a second query of a second table based on the first qualifier data obtained from the first query of the first table, the second query to obtain, from the second table, a plurality of blocks of reference signatures, the second table different than the first table.

17. The method of claim 16 , wherein the first qualifier data includes a first timestamp associated with a first block of reference signatures including the reference signature, the first qualifier data also including first media identification data identifying first reference media represented by the reference signature.

18. The method of claim 17 , further including crediting media, monitored at a monitored site, as corresponding to the first reference media represented by the reference signature when the prequalification of the first hash key is successful.