This is the use of quotation marks (" ") to locate documents with distinctive string of words or phrases such as “food security”, “climate change”, “tomato pests in Tanzania”. If a phrase is not specified in a search statement, the default search is one in which any of the words may be present. This can lead to thousands of useless hits.
Much electronic searching is based on the Boolean logic. This refers to the logical relationship among search terms and it consists of three logical operators: OR, AND, NOT. However, most search engines tend to use arithmetic operators/ templates/statements in the place of conventional Boolean operators. For example:
- Most search engines use AND as default. That means a space between search terms defaults to AND
- + is sometimes similar to AND
- - is similar to NOT
- Some databases offer search templates whereby users choose Booleans from a menu
- Logical operators can be expressed with substitute language (e.g. Google advanced search)
AND: This operator retrieves documents in which ALL search terms are present. It tends to narrow down a search and make it focused. For example, the search query environment AND development AND poverty retrieves documents that contain all three words i.e. development, environment and poverty.
OR: This operator retrieves records that contain EITHER of the search terms. Since it broadens a search and make it less focused, this operator is often used when searching for synonyms. For example, the search query “poultry diseases” OR “chicken diseases” retrieves documents that contain either of the search terms.
NOT: This operator excludes documents that contain the keywords you do not want. It retrieves your first word but excludes the second. For example, “gender violence” NOT children retrieves documents that contain only the term “gender violence” but not children.
There are search operators that work with several search engines to help you refine your search. It is important to observe the syntax when using these operators. For example, these search operators should be written in lower case. Sometimes there no spaces between the operators and search terms. Such operators include:
- intitle: This restricts results to those with specified term in the title. For example, the search query intitle:sunflowerretrieves documents with the word sunflower in the titles.Use allintitle for two and more terms e.g. allintitle:comparative embryology.
- allintext: This searches for multiple words in the body of the search result. E.g.allintext:fruit vegetable cultivation
- filetype:This restricts results to files ending in various formats such as doc, xls, ppt, pdf, rtf. For example, the search query “vertebrate anatomy” filetype:pdf retrieves only pdf documents that contain the phrasevertebrate anatomy.
- inurl: This restricts the results to websites that have the term in the address (URL). g. inurl:pasture. Use allinurlfor multiple words.
- site: This restrict your search results to the site you specify. For example, the query climate change site:www.fao.org retrieves documents with the terms climate and change only from the FAO website.
- define: This searches for definitions of words from various web sources. E.g. define:globalization
- It is possible to combine various search operators. g. allintitle:climate change filetype:pdf
- Some search engines provide tools to restrict your search according to date, geographical location, author, language, usage rights, safe search.
Truncation and Wild Card symbols
In some cases, search engines just search for exactly what you type in. Truncation and wild card symbols can be used to overcome this limitation. These symbols can be substituted for letters to retrieve variant spellings and word endings. Truncation symbols differ depending on database, but mainly an asterisk (*) is used. E.g. agricultur* will retrieve documents with the terms agriculture, agricultural, agriculturalist. However, a number of web search engines such as Google do not allow wildcards to be used for variable ends of words.Instead, such engines search for all possible word variations. Some databases support truncation in phrases. For example, searching the query “poverty * strategies" retrieves documents that contain the phrases poverty reduction strategies,poverty alleviation strategies, poverty elimination strategies.
Please download our compendium for more search techniques.