4.2 What is Boolean Logic?
Using 'Boolean Logic' is the traditional and effective way of searching for items in a database, and works on many search engines. It relies on the 'operators' AND, OR and NOT and also brackets ( ) and truncation (see below) to define very precise searches, which address the issues raised in the previous section.
For instance, imagine a database of documents about cats,
dogs and fleas
which contains:
- 10,000 items just about cats
- 10,000 items just about dogs
- 10,000 items just about fleas
- 50 items about both fleas and dogs
- 100 items about all of fleas, dogs and cats
This is represented on the Venn diagram right.
Move your mouse over the different searches
below to see
what they would retrieve ...
You can see, if you move your mouse over the above
examples that the use of
OR, AND and NOT lets you
conduct very precise searches to pick out different
sets of results, depending on what you want to find.
You should also be aware of 'truncation' (also known as stemming or using wildcards) ... this is the common option of using a character like * or ? to search for words that have the same root:
eg. train* would find train, trainer, training, trains
Finally, bear in mind that quotation marks are often used to designate a phrase, eg. "love of god" will find only items containing that particular phrase and not just items that mention 'god' in one paragraph and 'love' in another.
