Venn Diagrams

Venn diagrams are a useful way to visualize Boolean logic.

AND looks like this:

low and cholesterol	sheep and cattle and chickens	coins and (francs or pesos)

Scenarios: 

I need articles about low cholesterol.
He needs information about running a farm with sheep, cattle, and chickens.
She need francs and pesos in coins.

OR looks like this:

major or minor	grilled or poached	circle or square

Scenarios:

We would like to attend a Spring training baseball game; we don't care if it is major league or the minors--or if it is a match between the two.  What games are available?
This cookout/potluck is great!  I'll eat either the grilled or poached salmon--or both if there isn't enough of one or the other.
They don't care if the coasters we buy them are shaped like a circle or square.

• Exclusive or.  There is an exclusive or, but it is not used in most library databases.  The majority of library researchers will never run across a database which uses the exclusive or.

  oil or water   [exclusive OR]

Scenario:  She is doing experiments, but she will never mix oil and water together.  -->To find these results in one search in a library database she will need to do her search like this: (oil not water) or (water not oil).

NOT looks like this:

chips not pretzels

Scenario:  He'll eat chips, but not if there are pretzels in the same bowl.

Real life search:  You do a word search for items in SAGE on solar houses. One of the items you find is Solar Homes and Sun Heating.

This can be shown on a Venn diagram like this:

solar and houses

Notice that the Venn diagram has a circle for "heating."   Even though you did not search for "heating" you found a record with "heating" as one of the subject terms.  Most of the time when you do a search, the records you pull up have several words that you did not specifically put in your search.  This is OK--and to be expected.  It is also a good way to find additional terms you might want to search.

If you had searched for all three, solar and houses and heating, your Venn diagram would look like this:

 

Your result set would not include the items in the set below:

(solar and houses) not heating

Looking at the big picture:

When you are doing advanced research, you may find yourself searching a database with a subject focus.  In this case, you don't need--or want--to do keyword searches for the general topic.

For example, in ERIC (an educational index), if you are looking for teaching tools in textbooks as well as suggested exercises, just search "textbooks and exercises"--there is no need to type "teaching" also. However, in this case you will probably want to add something about your targeted age group--or your search results may contain many irrelevant (to you) sources.

textbook and exercises	textbooks and exercises and grade 8

If you are beginning searcher you might find it worth your while to draw Venn diagrams before doing your searches--even advanced searchers use them from time to time.