The fuller name, Okapi BM25, includes the name of the first system to use it, which was the Okapi information retrieval system, implemented at London's City University[1] in the 1980s and 1990s

1 200 OK Date: Thu, 02 Jul 2026 17:06:57 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"5c10b5686e0c159df9d5da5670da3dcd" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 19:46:58 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"224585a2a0e3e3163a01d12f9ff2f6bf" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 19:46:47 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"7a76809f6ec3aafe1d4cbdfbcf13223d" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 19:47:30 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"1ac518a72b4901f1a5a68408c23cf2a7" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 16:54:32 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"265baa85c7684e28d15c55e0a43ae54c" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 16:53:48 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"3c1b1e9e1490fb726e22e11ab6788493" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 21:47:09 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"764842f7a6fd6df0a8d57caaf9c860d1" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 16:54:21 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"26dfd90bfcac5e8fd65691a38e8d86b0" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 16:53:59 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"563ef1aa4a8f6d2e7b65a34501152d39" Cache-Control: max-age=0, private, must-revalidate Strict

S-Class Information Retrieval The empirically validated retrieval progression is BM25 then learned-sparse then dense then hybrid fusion with re-ranking

1 200 OK Date: Thu, 02 Jul 2026 17:07:19 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"7f53a7c4a1b003e79f3563086b10bf3a" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 19:47:09 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"4ad4d37c9015c110ecc0e7ddb593aeec" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 16:54:10 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"554c4addd0da505c1c2f60255b83a6e8" Cache-Control: max-age=0, private, must-revalidate Strict

1 200 OK Date: Thu, 02 Jul 2026 17:06:44 GMT Content-Type: text/html; charset=utf-8 Vary: X-PJAX, X-PJAX-Container, Turbo-Visit, Turbo-Frame, X-Requested-With, Sec-Fetch-Site,Accept-Encoding, Accept, X-Requested-With ETag: W/"47aa9c1d17c88f3a190a8326a978c3c3" Cache-Control: max-age=0, private, must-revalidate Strict

NOTE: ACM DL title omits the trailing word Research; the project site and arXiv include it

[7] It was initially available for download from its home at the SourceForge web site

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server: ATS/9.2.13 x-content-type-options: nosniff content-language: en accept-ch: reporting-endpoints: csp-report-to-endpoint='/w/api.php?action=cspreport&format=json'; content-security-policy: script-src 'unsafe-eval' blob: 'self' meta.

com\n |date=28 February 2020\n |access-date=18 April 2021\n}}</ref> and contributors<ref>\n{{LSR\n |url=https://github

In other projects Wikimedia Commons Wikidata item Appearance move to sidebar hide From Wikipedia, the free encyclopedia American photo storage and image hosting website Photobucket Type of site Image hosting service Available in English Owner Photobucket

server: ATS/9.2.13 x-content-type-options: nosniff content-language: en accept-ch: reporting-endpoints: csp-report-to-endpoint='/w/api.php?action=cspreport&format=json'; content-security-policy: script-src 'unsafe-eval' blob: 'self' meta.

## Communications If you think you've identified a security issue in the project, please *DO NOT* report the issue publicly via the GitHub issue tracker, mailing list, or IRC

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[ 1 ] It is a commonplace feature of instant messaging , Email clients , online games and mobile phones

server: ATS/9.2.13 x-content-type-options: nosniff content-language: en accept-ch: reporting-endpoints: csp-report-to-endpoint='/w/api.php?action=cspreport&format=json'; content-security-policy: script-src 'unsafe-eval' blob: 'self' meta.

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server: mw-web.codfw.main-59656c8c96-nwmcm x-content-type-options: nosniff content-language: en accept-ch: reporting-endpoints: csp-report-to-endpoint='/w/api.php?action=cspreport&format=json'; content-security-policy: script-src 'unsafe

This article includes a list of general references , but it lacks sufficient corresponding inline citations