Usage in Commercial Search Engines
In regards to implicit/automatic versus explicit proximity search, as of November 2008, most Internet search engines only implement an implicit proximity search functionality. That is, they automatically rank those search results higher where the user keywords have a good "overall proximity score" in such results. If only two keywords are in the search query, this has no difference from an explicit proximity search which puts a NEAR operator between the two keywords. However, if three or more than three keywords are present, it is often important for the user to specify which subsets of these keywords expect a proximity in search results. This is useful if the user wants to do a prior art search (e.g. finding an existing approach to complete a specific task, finding a document that discloses a system that exhibits a procedural behavior collaboratively conducted by several components and links between these components).
Web search engines which support proximity search via an explicit proximity operator in their query language include Walhello, Exalead, Yandex, Yahoo! and Altavista:
- When using the Walhello search-engine, the proximity can be defined by the number of characters between the keywords.
- The search engine Exalead allows the user to specify the required proximity, as the maximum number of words between keywords. The syntax is (keyword1 NEAR/n keyword2) where n is the number of words.
- Yandex uses the syntax keyword1 /n keyword2 to search for two keywords separated by at most words, and supports a few other variations of this syntax.
- Yahoo! and Altavista both support an undocumented NEAR operator. The syntax is keyword1 NEAR keyword2.
- Google supports AROUND(#).
Ordered search within the Google and Yahoo! search engines is possible using the asterisk (*) full-word wildcards: in Google this matches one or more words, and an in Yahoo! Search this matches exactly one word. (This is easily verified by searching for the following phrase in both Google and Yahoo!: "addictive * of biblioscopy".)
To emulate unordered search of the NEAR operator can be done using a combination of ordered searches. For example, to specify a close co-occurrence of "house" and "dog", the following search-expression could be specified: "house dog" OR "dog house" OR "house * dog" OR "dog * house" OR "house * * dog" OR "dog * * house".
Read more about this topic: Proximity Search (text)
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