Information-retrieval methods

Search words are combined into search phrases in information retrieval. To master the methods of information retrieval, you need to know:

  • search phrases and Boolean operators
  • truncation of search words
  • phrase search
  • limiting the search field

Search phrases and Boolean operators

You can combine the terms you have found into search phrases, if you cannot describe your search in one word. To combine search words, you need the Boolean operators AND, OR and NOT. Use capitals for operators, as not all databases recognise operators written in small letters.    

Use the operator AND when you want all the search words to appear in the search result. In this way, this operator limits the search result.

Example: You need publications that discuss the health effects of chocolate. The search phrase “chocolate AND health” retrieves all publications that contain the words “chocolate” and the word “health”. This can be illustrated:

AND operator (chocolate AND health)

  • the circle marked chocolate (yellow and green) contains the publications with the word ‘chocolate’.
  • the circle marked health (blue and green) contains the publications with the word ‘health’.
  • the search result shows the area marked AND (the green intersection of the yellow and the blue circle).
  • You can often leave out the word AND if it is used as the default operator in the database. In this case, the search phrase “chocolate health” corresponds to the search phrase “chocolate AND health”.  

The operator OR is used when we want one of the search words to occur in the search result, so this operator expands the search result.

Example: You need more information on the health effects of chocolate, and the search phrase of the previous example did not yield enough search results. Thus, it might be useful to run a search in some other languages. This could be something like “chocolate OR suklaa”. The search results include all publications that contain the word “chocolate” or the word “suklaa” – and, of course, some publications that contain both.

A search phrase for ‘chocolate’ or a related term ‘cocoa’ can be illustrated:

OR operator (chocolate OR cocoa)

  • the circle marked chocolate contains the publications with the word ‘chocolate’.
  • the circle marked ‘cocoa’ contains the publication with the word ‘cocoa’.
  • the search result includes the areas marked chocolate, OR and cocoa.

The operator NOT is used when we want to exclude a word from the search result. You have to be careful when using this operator, since it may exclude very useful information by mistake.

Example: You still need more information on the health effects of chocolate, but you have already found enough articles concerning weight gain. The search “health NOT weight gain” yields all the publications that contain the word “health” but not the phrase “weight gain”. The same illustrated:

NOT operator (health NOT “weight gain”)

  • the area marked health (green circle and the sectioned blue piece) contains the publications with the word ‘health’.
  • the circle marked “weight gain” (blue) contains the publications with the word ‘weight gain’.
  • the search result will give the area (green) marked health in the circle

Use of operators

You can use operators in different types of databases; library collection databases, various reference and full-text databases, and Internet search engines. The operators may have different names in other search programs: logical operators, Boolean logic or search commands. They can also be expressed in other words in a natural language (e.g. JA, AND) or characters (e.g. +, &).

Use parentheses () in the search phrase to clarify the search when you use several different operators, for example. The search engine will look for the search phrase inside the parenthesis first, and then combines the search phrases with each other.

Example: You need information about chocolates health benefits. The search

(chocolate OR cocoa) AND (health OR “weight gain”)

will give you a result with publications that contain at least one of the words ‘chocolate’, ‘cocoa’ and at least one of the words ‘health’ or ‘weight gain’.

Truncating search words

You can leave out a part of the end of the search word, this is called truncating. If you do not truncate search words, part of the result may be omitted because the search engine looks for words in exactly the form they are entered into the search engine. This is an important point if you are looking for information in Finnish (because of different word endings). In English, words are often spelled differently in British and American English (e.g. behavior vs. behaviour).

Truncation is marked with a truncation character or so-called joker sign. The most common joker sign is * (but also ?, # or $ are used sometimes). Often, it is also possible to exchange one or more characters in the middle of a word because of different spellings. As different databases use different characters for splitting and replacing words, please check the characters used from each separate database: for instance, in Helka, the character * is used for breaking off the search term.

Some general examples of the use of joker signs:

  • market* (will give the result on market and marketing
  • organi$ation (organisation or organization)
  • ?sonic (subsonic, supersonic, etc)

Always consider carefully where to truncate a search word. If you cut it too short, it may turn up results that you are not interested in. A search on emu*, for example, will turn up ’emu’, ’emulate’, ’emulsifier’, ’emulsify’, ’emulsion’, etc. please note that in some search engines, like Google, you cannot truncate words at all!

Phrase search

When you use several search words in a normal word search, it does not matter in which order the words are; the search phrase

donald duck

for example, could turn up a reference or page where a person called Donald Pizarro described his delicious duck recipe for Canneton à l’Orange.

With a phrase search the search engine will look for exactly the character string in the search phrase, in the same order. The phrase should usually be entered in citation marks, which means that the searches

“academic writing”
“gekko reproduction”
“Seven brothers”

will give a result answering to the exact phrase. Phrase search is especially useful for information-retrieval from full-text databases and with Internet search engines.

Example of searching for a phrase in the Proquest database: When searching for a book, such as Positive education, use quotation marks.

Search box in the Eric database. In phrase search, use quotes around “positive psychology”.

Limiting the search field

You can specify the search by limiting the search field. This will give you a more exact match, since the search results that fall outside the limit are left out. Commonly used limits are a certain period of time, a certain language or country.

The search field can usually be limited with the search form, where you can select e.g. which database field to limit.

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Watch the video about search phrases and Boolean operators. Duration of video 1 min 52 sec.