Boolean: AND / OR / NOT
You walk into a library or book store and ask to see all the books about lions and tigers. You want the books with information about both lions and tigers because you are doing a study about how lions and tigers interact in the wilds of India. Some of the books are only about lions and some are only about tigers. Some, however, are about both lions and tigers. In the illustration below, the whole left circle is filled with books about lions and the whole right circle has books about tigers. The books that fall in the darkest area have information about both lions AND tigers. This is the Boolean AND. Let’s say we asked for books about lions AND tigers AND bears (Oh my!). Notice that when we add another animal to our book needs, the darkest area is smaller meaning we get fewer books.
This process is not like addition in that you get more when you say 1 and 1 equals 2 (more than 1). Every time you add another word by combining it with an AND, you will get fewer results: you will find fewer books or articles. The other thing to note is that most databases default to an AND combination. In other words, if you do not tell the database how you want the words combined and you have typed in more than one word, the database will most likely (but not always) combine them for you using AND. A common mistake is to keep adding words to a search in anticipation that the results will grow. Now you know why that does not work. Having said that, most of the time you are going to want to use the AND search because it captures the multiple concepts of your topic.
Relating this to the grid you made, the Boolean AND is used between terms in different rows.
The Boolean OR and Boolean NOT are trickier than they look. The results they give you can include many resources off topic in the case of the OR and miss many in the case of the NOT. When used correctly, they can be powerful tools.
Boolean OR gets you anything and everything that has either and all the words you type in. It is often used with synonyms:
teens OR youth OR adolescents.
If, for example, your topic was the big cats of India, you would want books about lions, books about tigers and books that are about both lions and tigers. This is when you would use the Boolean OR.
Relating this to the grid you made, the Boolean OR is used between terms in the same row.
The Boolean NOT omits terms from your search. An example of a good use of the Boolean NOT would be if you are interested in the Dolphin habitat off the coast of Miami and you were retrieving a lot of information about the Miami Dolphins football team. Since it is completely off topic, you could try NOT football.
Caution is necessary, however, because the Boolean NOT can end up omitting resources you might want unless you are careful how you use it. Let’s say you are only interested in information about lions, but your results keep coming up with a bunch of tiger books as well. To eliminate the books about tigers, you use a Boolean NOT and type in NOT tigers. What you have eliminated are any books with the word tiger even if it has some very good information about lions and that would be bad.
We have covered the Boolean AND, OR and NOT. You will find that most database help screens call them operators and require that you type them with capital letters if typing them is required. The suggestion here is that you depend on multiple AND searches and do not make using OR and NOT your “go-to” operators. If you choose to try more than one operator in a search (an AND and an OR, for example) check with your librarians. It is a bit more complex than it looks and requires a bit more finesse than we will cover in this text.
We will talk more about searching the web later, but let’s take a detour for just a moment to discuss what Google’s advanced search calls the Boolean operators.
- AND: All of these words (that you have typed in)
- OR: Any of these words (that you have typed in)
- NOT: None of the words (that you have typed in)
Searching Google is merely searching another database so most, if not all, of the database tips apply.
Another important and often used way to combine words in a search is called phrase searching.
If you have two or more words and you want to find them right next to each other and in the order that you have typed them in, put them in quotation marks. Think of a multiword phrase that captures one concept. For example Sierra Nevada Mountains, storm drains, ice cream, Miami Dolphins, post office, jump rope and so on. If we combine the words Sierra Nevada Mountains with an AND, we could get resources (e.g. books or articles) that discuss the Sierra Trading Company’s new boots they call Nevada that are great in the mountains. If we combine ice cream with an AND we would get resources that talk about an ice hockey team that says they will cream their opponent on the ice next week. If we combine post office with an AND, we would get search results with both words in it such as an article about a medical office set up in a research post in Antarctica. If we want those words found together so that they capture one concept in our search, we combine them by putting them in quotation marks e.g. “Sierra Nevada Mountains”, “ice cream”, “post office”. What might we get if we did not use quotes around jump rope.
It can come in handy although not all databases are set up to handle this kind of search. Check the database help screens for specifics on how to use this kind of search if you want to try it. Proximity searches will return results with two words or phrases that appear in the resource within so many words of each other. Some databases allow searching for the words within the same paragraph.
This is how it works in some databases: Perhaps an author speaks of the “mountains of the Sierra Nevada” and does not use the phrase “Sierra Nevada Mountains”. To catch information using that turn of phrase, you might type “Sierra Nevada” n/3 mountains. Between the terms or phrases use n/# for terms to be found within # of each other and w/# to find the first word # or less words before the second word or phrase. If you want football and Denver to appear within say, 3 words of each other, you would type football n/3 Denver. If you want them to be within 5 words of each other and in the same order that you type them, you would type football w/5 Denver. You can change the number to suit your search. (Where ever there is a # in this paragraph, substitute a number.) This is tricky especially since this too varies from database to database.
To recap, the three ways we discussed to combine your terms are 1) the Boolean operators, AND, OR and NOT 2) phrase searching by using quotation marks around more than one word or 3) proximity searching. To combine words to make a good search, we go back to the grid of alternative terms above: the grid about the drought in California and how it affects redwoods. You can combine any word on one line with a word on a different line with a Boolean AND. If you want to try using the Boolean OR you will combine words on the same line with an OR. Words that you want to find together you will type in quotation marks such as “Sierra Nevada Mountains” and “water shortage.” This is how the way you choose to combine your words relates to the grid above: the grid about the drought in California. It is why you need to be very careful on making an accurate grid as you add alternative words to it. Here are two examples of what you could type into a database. Truncation is added for a more complete search.
“water shortage*” AND redwood*
Or something like this
drought AND Sequoia*