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Guide for Nanjing Institute of Technology (NJIT) students: Combining search terms

Designing a search string

With the help of a search string you will get the most versatile search possibilities when you are looking for comprehensive information on a certain topic.

As an example, a search about the topic "environmental effects of plastic waste".

  • Begin the search by grouping your topic into central subject matters. When brainstorming for search terms you can use a mind map. Do not use very general terms in your search such as effects.
    • Search terms: plastic waste, environment
  • Think about broader, narrower, parallel terms and different types of writing.
    • ​ litter plastic, plastic bottles, pollution
  • Select the appropriate keywords and form a search string.
    • Combine synonyms and parallel terms, for example, on the same line with an OR operator (Note: Use parentheses in Command search)​
    • Connect the subject matters with the AND operator
    • Also use truncation (*) and replacement character (?) if necessary
    • Use a phrase (" ") when you want the search terms to occur consecutively in the search results.

 An example search string:

"plastic waste" OR "litter plastic"

AND

environment* OR pollut*

The example picture information has been searched on the environmental effects of plastic waste in Scopus database.
Picture: Scopus <https://www.scopus.com/search> 13.6.2018

 

 

When you search with more than one search word, you need to tell the search engine what the relationship between the words is. For that we use Boolean operators:

  • OR operator with alternative words
  • AND operator with compulsory words
  • NOT operator to exclude a word.

The order of operations is usually AND before OR. You can override the order by using paranthesis ().

Databases have search boxes where you type in the search words and operators.

Some databases (e.g. Oula-Finna) require that the Boolean operators be capitalized, but with most other databases it does not matter.

Search order

Databases usually recognize AND as the primary operator, and will connect concepts with AND together first.  The order can, however, be defined by using parentheses. Parentheses define the order by first combining the search terms inside them. Without parentheses the order is determined by the database.

Boole

When, for example, you want references which, in addition to sugar, include either milk or cream. 

- The search (milk OR cream) AND sugar will always work correctly.

- Instead, the result of the search milk OR cream AND sugar depends on the database:

  • if the database performs AND first (e.g. Web of Science database), the search does not work as intended, because it finds references which have to include only milk or include both cream and sugar
  • if the database performs OR first (e.g. Scopus database), the search works as intended and finds references which have to include sugar and either milk or cream.

 

 

 

​Databases also have search fields which define the order between AND and OR operators depending on the database. For example, in the advanced search in Oula-Finna database the search fields are combined by always performing AND operator first, and in IEEE Xplore database the order of the search fields moves down from the first one. 

You can check the order of the operators in the instructions of the database from the Database guides.