Module 1:
Using Boolean AND and OR in Library Catalogs and Databases |
©2020 by Chris Niemeyer, University of Missouri-St. Louis.
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If you are a student, knowing simple 'Boolean logic' will help you search for information in library catalogs and databases with precision, speed and ease.
Boolean logic is a system that helps you arrange keywords to properly find information in these sources. Screen2 |
We will demonstrate this search system using two Boolean 'operators' (sometimes called 'connectors').
These will be: AND and OR. Screen3 |
Day-to-day communication provides some insight into Boolean logic.
Imagine you have dined at a restaurant. A waiter asks what you would like for dessert, and you reply: "I would like apple pie OR chocolate cake." Screen4 |
Well ... which of the two deserts do you really want?
"I would like apple pie OR chocolate cake." Screen5 |
But if you say:
AND "I would like apple pie OR chocolate cake." "I would like apple pie AND chocolate cake." the request becomes understandable. Screen6 |
With this slight modification the waiter would understand that you want both types of dessert. Maybe a strange request, but also a comprehensible one.
"I would like apple pie AND chocolate cake." Screen7 |
You know more about Boolean logic than you think because we all know how to use or as well as and in everyday speech.
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Knowing this, you should be able to employ Boolean or and and in library databases and catalogs for similar reasons.
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Below is the search line for a library catalog. Imagine you type-in the following
keyword search that uses Boolean or:
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This is an unusual keyword search since the terms appear to have NOTHING to do with each other. ![]() Screen11 |
Yet the search will retrieve a huge number of hits in most library catalogs - so many, in fact, that a catalog might only display the top 1,000 or so. Go to a library catalog and try it yourself if you don't believe it.
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Why so many hits?
Using or between keywords means you are requesting that all terms be retrieved. ![]() Screen13 |
Faced with this literal request, the catalog returns EVERY record that contains just ONE of your keywords.
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So, every record mentioning lightning will be retrieved, along with every record mentioning Cleopatra, along with every record mentioning hummingbirds, along with every record mentioning econometrics! ![]() A gigantic set of book records, most of which will have NOTHING to do with each other! Screen15 |
But the situation is radically changed when one uses and between search terms....
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In such a case, the keyword search will almost certainly return zero hits! Go to a library catalog and try it yourself if you don't believe it.
![]() Why zero search results?... Screen17 |
ALL keywords must be present in every single record whenever Boolean and is used exclusively between search terms. Boolean and narrows searches. Remember: we are searching for books in a regular library catalog.
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Library catalog records for books can be pretty spare. They try to describe the content of a book as concisely as possible. They might link to the full-text of a book but they won't have the full-text themselves.
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Knowing this, is is unlikely to find records in a library catalog for books about lightning, Cleopatra, birds of the family Trochilidae (hummingbirds were unknown to the Ancient Egyptians) and econometrics, a social science that uses mathematical modeling to understand economic activity.
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Once more, Boolean and narrows a search so that all keywords MUST be present in every single record.
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Just like in everyday speech, Using AND/OR in keyword searches produces quite different results depending on which of the two words you use.
![]() We will show an example of a helpful Boolean keyword search in the next module. Module finished! Screen22 |