Combining Search Terms into a Search Query

Boolean operators are used with alternative search terms. In information retrieval, there are three Boolean operators: AND, OR and NOT. Search terms and phrases with the operators that connect them can all be parts of the search query. One sentence may have one or more operators depending on the subject. Usually, it does not matter whether the operators are written in capital letters or not. UEF Primo and PubMed make an exception and require operators written in capital letters. In this learning material, operators are always written in capital letters for clarity.

Phrases and Boolean operators do not always have to be included in the search query. The idea is that the use of search terms, phrases and operators fits the purpose of the search and provides enough relevant matches for the search topic.

The AND operator narrows and focuses the search

When doing searches in a database, placing the AND operator between search terms means that you want to find the publications (i.e., records) where the search words to the left and right of the operator occur simultaneously. The AND operator is used to connect search terms with each other.

The AND operator is used to combine search terms that are dependent of each other or in a causal or influential relationship (for example: exercise AND health). Generally, AND does not mean the same as the word “and” in natural language. In human language, the following form of expression is often used: “the effect of concept 1 and concept 2 on concept 3”. In reality, however, the aim is to learn about the impact of either concept 1 or concept 2 or both on concept 3. In such case, AND would limit the search result too much if it were to combine all concepts.

Using AND operators between search terms focuses the search: the more limiting search terms are used, the more specific the search will be, and thus there will (in theory) be fewer results.

The OR operator broadens the search

The OR operator tells the database’s search engine that you want to find all publications (i.e., records) that contain at least one of the search words to the left or right of the OR operator. The records that feature both search terms will also appear among the results.

The OR operator is used to connect two alternative search terms that describe the same concept, such as synonyms or coordinate concepts. The more alternative expressions are included in the search, the more matches will be found.

Do note that the use of the OR operator is redundant when the alternative word also covers a more specific term, which would often be a phrase. For example, in the query “defence mechanism” OR defence, the word defenceis sufficient for also finding records that include defence mechanism.

The NOT operator is used to exclude certain search terms

The NOT operator tells the search engine to exclude from the results those publications (e.g., records) that have the search term to the right of the NOT operator. Unlike the AND and OR operators, the NOT operator does not include the subsequent word in the search but excludes it in order to focus the search instead.

The NOT operation is used less regularly, and as it may exclude relevant records from the search, it should be used with consideration. The NOT operator can also exclude useful records from the search result.

Advanced information retrieval includes the use of phrase search, truncation, and the Boolean operators

A search phrase can be simple and short or longer and more versatile. More important than length is that the search phrase achieves the goals and needs of the information retrieval, i.e., results in literature that answers the search question. Sometimes it may be necessary to build a search phrase using several techniques, such as truncation, phrases and the AND, OR and NOT operators.

A table or other visualizations can be used to outline how the search words could be combined. This is especially useful if you need queries with multiple search terms and operators.