Choosing and combining search terms

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Choosing search terms

Search terms are often subject keywords but can also be names, molecular formulae, significant numbers, depending on what you are searching for and the source you are using. This page is focused on choosing subject keywords.

A good way to identify the important search terms for a search:

  1. Define the subject in one sentence, for example;
    • The impact of coastal pollution in Britain

  2. Split this sentence into concepts, discarding words which merely describe the relationship between one concept and another;
    • Coastal Pollution Britain

  3. For each of the concepts think of synonyms (words with similar meaning) or related terms that would be useful. Some databases, abstracts and indexes have a thesaurus which can help. Look up your terms in the thesaurus and this will tell you related or preferred terms, for example:
    • Costal; coast, coasts, beach, beaches
    • Pollution; oil, sewage
    • Britain; United Kingdom, UK, England, Scotland, Wales, British Isles, Ireland

  4. Use these terms in your search. The way that you input and combine terms will depend on the source that you are using. Most databases, and Library Search, allow you to add truncation or masking symbols to words. For example, entering coast* into a catalogue search will find any word beginning with coast, including coast, coasts and coastal. A printed guide to 'Advanced searching on the Web catalogue' explains more fully, as does help on the system. Some databases use a thesaurus or controlled indexing which will help you to choose the preferred term, and indicate related terms. If you are searching for more than one search term see combining search terms below.

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Combining search terms in your searches

When you carry out a search on Library Search, it automatically 'links' the search terms you have input and displays results which have all the terms present, i.e. term 1 and term 2 and .... However, on the Library Search and most other databases, you can specify how the search terms are combined. To do this you need to use Boolean logic or logical operators, AND, OR, and NOT or their equivalents on the system you are using. The following examples show how the different operators work.  Advice on how to use these when you are using Library Search is given in the Search tips section of the Library Search help.


Use AND if you want to retrieve references that contain both of the terms you are using. This can narrow a search to find fewer, more relevant, references.

 diagram showing AND results
eg Pollution AND Oil spills

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Use OR if you want to retrieve references that contain either one of the terms you are using, or both terms together.
This can broaden a search to find more references.

 diagram showing OR results
eg Pollution OR Oil spills

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Use NOT if you want to exclude references that contain a particular term. Use with caution!

 diagram showing NOT results
eg Pollution NOT Oil spills

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Also, many databases allow you to use brackets to make more complicated searches, for example:

(Pollution OR Oil) AND Seabirds.

The brackets indicate the order that the combining of terms is made in.

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Many databases allow you to search for phrases, ie a number of words in a sequence together, for example in Library Search and Google you can search for phrases in this way:

"Oil pollution"

The quotation marks indicate that this should be searched for as a phrase, rather than as two words anywhere in the record.

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Alternatives to AND, OR, and NOT

Some databases and search engines may use other symbols in the place of AND, OR, and NOT.

For instance, with Google:

  • Pollution Seabirds is equivalent to Pollution AND Seabirds (the AND is implied)
  •  +oil means that oil must be present
  • OR is used as above
  •  -music is the equivalent of NOT music

To get the best out of search tools we recommend you look at the help on the system to find out how to enter and combine search terms effectively.

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