Boolean Search Techniques
Boolean Searching
Boolean searching is a logical method of connecting search terms using AND, OR, and NOT (known as "Boolean Operators") to narrow, expand, or exclude information in a search.
Named after the mathematician, George Boole, Boolean operators (A set of terms (AND, OR, and NOT) that are used in between keywords and phrases to help create a more precise search.), are used as conjunctions that combine or exclude certain keywords in your search. Though Boolean operators are used in logic, mathematics, and computer science, there are three common Boolean operators used by search engines (e.g., library catalogs, academic databases, and some online search engines). Think of Boolean operators as instructions that tell a search engine what to do with your keywords. Some search tools need Boolean operators to be typed in all capital letters in order for them to work, so it is a good idea to always type them in all caps whenever you are using them.
AND – If the main idea contains two or more ideas, you’ll want to use AND to combine those terms in your search statement. To look for information about spiders as signs of climate change, you’ll want to have both terms in the search and perform an AND search. That’s what automatically happens in search engines such as Google and Bing unless you tell them to do something different by using OR,NOT, or-.
OR – If the main idea has several synonyms, use OR to combine them. Most search tools search for all terms (AND) by default, so you need to use the operator OR between terms to let them know you want to find any of the terms not documents with all the terms. For instance, in the previous example of Latino small business growth, we would want to also use the term Hispanic.
NOT – If the main idea has a common use you want to exclude, use NOT to exclude that word. For example, if we were looking for information about illegal drug use we would want to exclude prescription drugs from the search results. This is commonly done with NOT or the use of the minus (-) sign. In Google, to exclude a word use-word with no space between the – and the word you want to exclude. If you put a space in there, Google will not exclude the word.(When using some search tools, you have to use AND NOT before the word to exclude it.)
Images from “Search Statements” by Teaching & Learning, Ohio State University Libraries, licensed under CC BY 4.0
Emily Wixson, Boolean Operators, https://www.youtube.com/watch?v=xsSZps3NH-M
Database Search Tips
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The key to being a savvy online searcher is to use common search techniques that you can apply to almost any database, including article databases, online catalogs and even commercial search engines.
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This is important because searching library databases is a bit different from searching Google.
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The techniques described in this section will enable you to quickly retrieve relevant information from the thousands of records in a database.
What is a database?
According to Encyclopedia Britannica: database, also called electronic database, is a collection of data, or information, specially organized for rapid search and retrieval by a computer.
A library database is a searchable electronic index of published, reliable resources. Databases provide access to research materials from academic journals, newspapers, and magazines. Some databases also include e-books, relevant Web resources, and various multimedia.
What to look for:
Boolean operators form the basis of mathematical sets and database logic.
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They connect your search words together to either narrow or broaden your set of results.
- The three basic boolean operators are: AND, OR, and NOT.
Why use Boolean operators?
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To focus a search, particularly when your topic contains multiple search terms.
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To connect various pieces of information to find exactly what you're looking for.
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Example:
second creation (title) AND wilmut and campbell (author) AND 2000 (year)
Search Order:
Databases follow commands you type in and return results based on those commands. Be aware of the logical order in which words are connected when using Boolean operators:
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Databases usually recognize AND as the primary operator, and will connect concepts with AND together first.
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If you use a combination of AND and OR operators in a search, enclose the words to be "ORed" together in parentheses.
Examples:
- ethics AND (cloning OR reproductive techniques)
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(ethic* OR moral*) AND (bioengineering OR cloning)
Tutorials
What to look for:
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Root words that have multiple endings. Example: sun = suns, sunshine, sunny, sunlight
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Words that are spelled differently, but mean the same thing. Example: color, colour
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Truncation/wildcard symbols vary by database. Check the help screens to find out which symbols are used.
Truncation:
Truncation, also called stemming, is a technique that broadens your search to include various word endings and spellings.
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To use truncation, enter the root of a word and put the truncation symbol at the end.
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The database will return results that include any ending of that root word.
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Examples:
child* = child, childs, children, childrens, childhood
genetic* = genetic, genetics, genetically -
Truncation symbols may vary by database; common symbols include: *, !, ?, or #
Wildcards:
Similar to truncation, wildcards substitute a symbol for one letter of a word.
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This is useful if a word is spelled in different ways, but still has the same meaning.
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Examples:
wom!n = woman, women
colo?r = color, colour
What to look for:
To find subject headings for your topic:
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Look to see if the database has an online thesaurus to browse for subjects that match your topic (check the Help screens).
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Some databases publish thesauri in print (e.g. Thesaurus of Psychological Index Terms for the PsycInfo database).
Another way to find subject headings:
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Start with a keyword search, using words/phrases that describe your topic.
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Browse the results; choose 2 or 3 that are relevant.
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Look at the Subject or Descriptor field and note the terms used (write them down).
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Redo your search using those terms.
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Your results will be more precise than your initial keyword search.
What are subject headings and keywords?
Subject headings:
Describe the content of each item in a database. Use these headings to find relevant items on the same topic. Searching by subject headings (a.k.a. descriptors) is the most precise way to search article databases.
It is not easy to guess which subject headings are used in a given database. For example, the phone book's Yellow Pages use subject headings. If you look for "Movie Theatres" you will find nothing, as they are listed under the subject heading "Theatres - Movies."
Keyword searching:
Is how you typically search web search engines. Think of important words or phrases and type them in to get results.
Here are some key points about each type of search:
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Youtube video that explains the differences between keywords and subject headings.
What to look for:
Records in library databases are comprised of fields containing specific pieces of bibliographic information. Common fields include:
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author
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title
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journal title
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abstract
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publisher
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date/year of publication
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subject/descriptor
How database fields improve your search.
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Limiting your search to specific database fields can yield more precise results.
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For instance, if you are looking for articles by Elon Musk instead of about him, it is more efficient to limit your search to the author field.
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To find various fields within a database, look for drop down boxes or menus to select the field you want to search.
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Then combine words and fields together with boolean or proximity operators, depending on how precise you want to be.
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If you do not choose a specific field, the database usually reverts to a keyword search, where your words will be searched throughout the record.
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If your keyword search retrieves too many records (more than 50), try narrowing your search to retrieve a more manageable result.
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Information overload - too many results - can be a worse situation than finding only 10 very relevant results.
Examples of fields:
The record below shows the field names on the left: Title, Author, Source, Subject Terms, Abstract, etc.
What to look for:
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Different databases interpret searches differently. A common variation is how databases recognize phrases.
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Some assume that words typed next to each other should be searched as phrases.
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Others automatically put a Boolean AND between your search terms, requiring that all the words be present, but not necessarily adjacent to each other.
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These searches can retrieve very different results.
Phrase Searching Tips:
Most databases allow you to specify that adjacent words be searched as phrases.
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Using parentheses or quotes around search words is a common way to do phrase searching, but not all databases or search engines use them.
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Example: "genetic engineering"
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Hint: It is often very easy to do phrase searching from the Advanced or Guided search in a database.
Proximity Operators:
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Many databases allow you to specify that the words you are searching are within a certain proximity of each other.
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Proximity operators are more specific than Boolean operators and make your search more precise.
Proximity Operator Examples:
Proximity operators also vary by database, but some common ones include:
w# = with
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With specifies that words appear in the order you type them in.
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Substitute the # with a number of words that may appear in between. If no number is given, then it specifies an exact phrase.
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Examples:
genetic w engineering (searches the phrase genetic engineering)
Hillary w2 Clinton (retrieves Hillary Clinton, Hillary Rodham Clinton, etc.)
n# = near
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Near specifies that the words may appear in any order.
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Substitute the # with a number of words that may appear in between.
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Examples:
cloning n3 human (retrieves cloning of humans, human cloning etc.)
Consult the database Help screens to find out how to search by phrases or to specify proximity.
What to look for:
Stop words are frequently occurring, insignificant words that appear in a database record, article or web page.
Common stop words include:
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a
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an
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the
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in
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of
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on
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are
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be
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if
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into
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which
About Stop Words:
Why should you care about stop words?
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Many databases ignore common words from your search statement. If included, the database returns far too many results.
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So you know which words to exclude from your search statement.
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To make sure they are included if they are a significant part of your search.
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Many databases recognize common stop words when they are part of the controlled vocabulary of subject headings and descriptors. Example: balance of payments
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Stop words vary by database. Check the Help screens for a list.
How can you avoid using stop words in your search?
In some databases, you can use techniques to include stop words as part of the sear
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Some databases use quotes around stop words. Example: Title keyword= out "of" Africa retrieves title: Out of Africa
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Choose the most significant words that describe your topic and connect them together using Boolean operators or proximity operators.
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Search for your terms in specific fields, such as author, title or subject/descriptor.
The information for Database Search Tips was authored by Tina Chan at Massachusetts Institute of Technology, borrowed and adapted with permission by Nikki Crane, Taft College Library, May 21, 2019.