4. Boolean searching -- the operators AND, AND NOT, OR

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You have asked for pizza with pepperoni and ham, but without olives and garlic. Here's how your order will look using Boolean operators:

pizza AND pepperoni AND ham AND NOT olives AND NOT garlic.

A search engine would interpret this Boolean expression in the following way:

"The user wants me to show him or her links to all the pages that include the word pizza as well as the word pepperoni and the word ham, but he or she wants me to subtract pages that include the word olives or the word garlic.

It isn't poetry, but it is logical and it works. The operator AND means that the word that follows has to be in the text of the pages that are to be listed. Pages including the words following AND NOT will not be listed.

If you suspect that the restaurant is out of pepperoni, you may be a little more open-minded about this, and say: "I would like pepperoni or chicken". In Boolean terms that is:

pepperoni OR chicken

On the Net an order like this one will give you all the pages that include the word pepperoni, all the pages that include the word chicken and all the pages that include both of these words.

What happens if you take out the operators AND, AND NOT and OR and write the following line instead?

pizza pepperoni ham olives garlic

Most search engines interpret the space between the words as AND. That is, they will give you all the pages that include all these word. But that was not what you were looking for, was it? You are interested in pages that do not include the word olives or garlic, not in pages that have to include these words.

Then again, some engines may interpret the space between the words as OR. This means that they will even give you pages that include only one of these words. You will, for instance, end up with a lot of irrelevant information about the garlic industry.

At the moment true Boolean searching is supported by most of the major search engines.

In Pandia Plus and the Open Directory you must write ANDNOT in one word. Sorry about that!

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