Efficient retrieval algorithm by query term discrimination

1. A method for use in information retrieval, the method comprising:

for each of a plurality of terms, selecting a predetermined number of top scoring documents for the term to form a corresponding document set for the term;

receiving a query comprising a plurality of query terms;

ranking the plurality of query terms received in the query based at least in part on the corresponding document sets for each of the plurality of query terms, wherein the ranking comprises using an inverse document frequency algorithm;

selecting a number of ranked query terms from the plurality of query terms, wherein each selected ranked query term comprises its corresponding document set and each document in a respective document set comprises a document identification number;

forming a union set based on the document sets associated with the selected number of ranked query terms; and

for a document identification number in the union set, scanning a document set corresponding to an unselected query term for a matching document identification number, wherein the unselected query term is included in the query comprising the plurality of query terms.

2. The method of claim 1 , wherein the scanning comprises use of a pointer that indicates a scanning position in the document set corresponding to the unselected query term.

3. The method of claim 1 , wherein the scanning comprises use of jumping.

4. The method of claim 1 , wherein the scanning comprises use of jumping and binary searching.

5. The method of claim 1 , wherein the number of ranked query terms comprise two.

6. The method of claim 1 further comprising repeating the scanning for more than one document identification number in the union set.

7. The method of claim 1 , wherein the predetermined number of documents comprises a number less than 25.

8. The method of claim 1 further comprising, after a matching document identification number is determined from the scanning, comparing a document score associated with the matching document identification number in the document set corresponding to the unselected query term to a document score associated with the document identification number in the union set.

9. The method of claim 8 further comprising, based at least in part on the comparing, jumping a pointer for the document set corresponding to the unselected query term or binary searching in the document set corresponding to the unselected query term.

10. The method of claim 9 , wherein jumping occurs if the document score associated with a document identification number in the document set corresponding to the unselected query term is less than the document score associated with the document identification number in the union set.

11. The method of claim 9 , wherein binary searching occurs if the document score associated with a document identification number in the document set corresponding to the unselected query term is not less than the document score associated with the document identification number in the union set.

12. The method of claim 1 , wherein the scoring the documents comprises BM25 scoring.

13. The method of claim 1 further comprising outputting a list of documents.

14. One or more computer memory devices comprising computer-executable instructions to perform the method of claim 1 .

15. An offline method for use in online information retrieval, the method comprising:

for each of a plurality of terms, selecting a predetermined number of top scoring documents for the term to form a corresponding document set for the term; and

storing the document sets for subsequent access responsive to an online query;

receiving a query comprising a plurality of query terms;

ranking the plurality of query terms using an inverse document frequency algorithm;

selecting at least two ranked query terms from the plurality of query terms, wherein each selected, ranked query term comprises a corresponding document set of top scoring documents, wherein the selecting the at least two ranked query terms leaves at least one unselected query term from the plurality of query terms;

forming a union set based on the document sets associated with the at least two ranked query terms;

merging the union set with a document set corresponding to the at least one unselected query term; and

outputting results based on the merging.

16. The method of claim 15 , wherein the scoring comprises BM25 scoring and wherein the predetermined number of top scoring documents comprises a number less than 25.

17. One or more computer memory devices comprising computer-executable instructions to perform the method of claim 15 .

18. An online information retrieval method comprising:

receiving a query that comprises a plurality of terms;

accessing documents or information about documents;

based on the accessing, ranking the plurality of terms using an inverse document frequency algorithm;

selecting a number of ranked terms, wherein each selected ranked term comprises a corresponding document set and each document in a respective document set comprises a document identification number;

forming a union set based on the document sets associated with the selected number of ranked terms; and

for a document identification number in the union set, scanning a document set corresponding to an unselected term for a matching document identification number, wherein the unselected term is included in the query comprising the plurality of terms.

19. One or more computer memory devices comprising processor executable instructions to perform the method of claim 18 .