- What is Boolean search?
Boolean search allows you to construct queries that specify exactly the words that you do and don't want to see in your results. Three operators may be used: AND, OR, and NOT. They have these basic interpretations:
sheep AND deer: Find all documents containing the word sheep and the word deer.
sheep OR deer: Find all documents containing the word sheep or the word deer or both.
sheep NOT deer: Find all documents containing the word sheep but not the word deer.
The operators must be in all caps in order to be interpreted as Boolean.
Note that you can also use AND NOT as the equivalent of NOT, as in the query sheep AND NOT deer.
- How is Boolean search different from natural language search?
Natural language search takes into account the meanings of the words in your query. For example, if you ask How can I buy a camera phone?, the search will recognize phrases like camera phone as having a particular meaning with synonyms like phone cam or related terms like cell phone which may be also be recognized as a type of match. It will also not look for matches on common words like can, I, and a, which will not yield relevant results. Furthermore, there are likely to be rules which recognize the language patterns used to ask common questions, which will lead you directly to the best answer.
On the other hand, Boolean search can be useful when you want to target a particular set of words. In a Boolean search, synonyms and related terms are not searched on, (although other word forms may be included, as discussed in the next section). None of the words in your query will be skipped, and no other rules related to natural language interpretation will be used.
- How are the terms in my search interpreted?
If the words in your query can have other forms like plural or past tense, those variations will also be searched on. For example, if you search on manual NOT help, then your results may contain either the singular manual or the plural manuals, and they will not contain help or the verb forms helps, helped, or helping. Similarly, if you search on manuals NOT helping, all of these forms will still be used in your search.
Below are all the forms which are automatically included in your search:
| Nouns | singular | manual | child | mouse |
| plural | manuals | children | mice |
| Verbs | stem | help | run | log in |
| present tense | helps | runs | logs in |
| past tense | helped | ran | logged in |
| progressive tense | helping | running | logging in |
| Adjectives | simple | cheap | light | fast |
| comparative | cheaper | lighter | faster |
| superlative | cheapest | lightest | fastest |
- What if I have more than one word in a search term?
If your search includes multiple words in a single term, those words will be searched for as a unit. For example, if you search on camera phone AND manual, your results will contain camera phone or camera phones. A document containing the terms camera and phone with any words intervening will not be considered a match.
- What if I want the exact form of a word or phrase to be searched on?
You can use double quotes around a word or phrase to specify a search on the exact form. Suppose you want to find documents that contain camera phones but not camera phone plus either manual or manuals. Then you can submit the following query:
"camera phones" AND manual
Double quotes may only be placed around a single entire search term; the following searches are not correctly formed and will not generate a Boolean search:
Incorrect form: "camera" phones AND manual
Incorrect form: "camera phones AND manual"
- What happens if I use more than one operator in a search?
You can use multiple operators in your search to further narrow or expand your results. For example, you can ask:
camera AND phone OR phonecam
This search will yield documents containing forms of phonecam or containing forms of both camera and phone.
In this interpretation of the query, the AND operator takes precedence over the OR operator. That is, the phrase camera AND phone is grouped together before it is combined with phonecam OR .... This happens regardless of the order of the arguments, so the following queries have the same interpretation:
phonecam OR camera AND phone
camera AND phone OR phonecam
In general, the following operator precedence is observed:
NOT takes precedence over AND and OR
AND takes precedence over OR
This leads to the following interpretations:
x NOT y AND z: Retrieve documents containing both x and z, but not y.
x NOT y OR z: Retrieve documents containing x but not y, or containing z.
x AND y OR z: Retrieve documents containing both x and y, or containing z.
w AND x NOT y OR z: Retrieve documents containing w and containing x without y, or containing z.
w OR x NOT y NOT z: Retrieve documents containing w or containing x without y and without z.
- What if I want to enforce a different ordering on the operators in my query?
You can use parentheses to override the default ordering of the operators. For example, if you wanted to retrieve documents containing either term phone and phonecam plus the term camera, then you could use the following query:
(phonecam OR camera) AND phone
In general, you can use parentheses anywhere you want to override the default ordering or just be explicit about the query's interpretation. Below are some more examples of how queries with parentheses are interpreted:
a NOT (b OR c) OR d: Retrieve documents containing either a without b or c or containing d.
(a AND b) NOT (c AND d AND e): Retrieve documents containing both a and b, but not containing all the terms c, d, and e.
a NOT (b AND c OR d): Retrieve documents containing a, but not containing both b and c or containing d.
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