The techniques explained in this page will help you become the fast, effective searcher you really need to be as a distance learning student relying on online information sources. Not all the techniques covered here will be supported by all databases - you are advised to look at the help pages as you learn to use a new database since that will save you a lot of time and frustration.
What is Boolean Searching?
Most searches will return too many or too few records. It takes a long time to look at hundreds of records. By putting a little effort into constructing search strings (what you type into the search box) you can save a lot of time. The database can do a lot of work for you if you take the trouble to add a little sophistication to your search strings.
To do this with databases you need to know about the Boolean system. By the use of a few simple linking words, called operators, you can make your searches much more precise.
If your search returns too many records, you can narrow your search by adding more search terms. To make sure that all the records your search finds contain all the search terms, link them with the and operator. For example, let's say you were interested in only red cars. To avoid having to sift through records on blue cars, green cars and so on, you would use the following search string:
'red and cars'
If you do not wish to see records containing a certain term, you can exclude these by using the not operator. Be careful when using this, you may miss records that contain useful information because you have excluded too many records. With many databases you will need to use and not rather than not, check the help pages of the database if you are not sure. If you were interested in cars of any colour as long as they are not blue, you would use the following search string:
'cars not blue'
If your search returns few or no records, you might have more success if you can think of alternative search terms. This can include:
- other terms related to your topic
- synonyms (words with the same meaning)
- different word endings (singular and plural forms, for example)
- different spellings (UK versus US spelling, for example)
To search for records that return one or more of your search terms, link them together with the or operator. For example, cars are also known as automobiles and so to catch as many relevant records in your search as possible, you would use:
'cars or automobiles'
Proximity, Truncation and Wild Cards
The power of Boolean searching can be extended further by proximity, truncation and wild card operators. Proximity searching allows you to specify that records found by your search contain one search term near another. If, for example, you are interested in red cars, a search string such as
'red and cars'
may return irrelevant records because red is a very general adjective and could describe many other things in a record. The near operator requires that a record has terms close together in the text, making it more likely that there is a meaningful link between the terms in the record. Therefore one would use the search string:
'red near cars'
The syntax used for truncation varies amongst databases; e.g. sometimes next is used rather then near - you should check the databases' help pages to find out if and how proximity can be used.
Truncation allows you to search for all the variants of a word without having to specify them all in your search string. It is very useful to take into account plural and singular forms of a noun. For example,
asks the computer to search for both car and cars, or any word beginning with car such as carriage or carburettor. So, as with the not operator you have to be careful when using this operator or you may get a lot of irrelevant records. Think about how many words might start with a root such as car before using truncation. If you simply wish to include both the singular and the plural forms of a noun in your search you might be better off using the or operator:
'car or cars'
As for proximity, the syntax used for truncation varies amongst databases- you should check the databases' help pages to find out if and how truncation can be used.
Wildcards are rather like truncation, but rather than allowing for variation at the end of a word, it allows for variation in a character in the middle of a word. Wild cards are especially useful for taking into account variations in spelling. For example, many words can be spelt with an s or a z, e.g. realise/realize. You could use the or operator to get around this, but wild cards are much neater:
In the example above, any character can appear between the i and e. Again, syntax can vary between databases, sometimes ? is used - check the help pages!
Putting it all together
Using Boolean operators it is possible to construct complex strings of search terms. To make sure the computer does exactly what you want it to, you need to use brackets (parenthesis) to make the structure of your search string clear. Let us continue with our example. We have decided that it would be best to use "car or cars" rather than to use truncation (car*). We also want to specify that the word red occurs near car or cars. You could use the search string:
'red near car or cars'
There is a danger that the database will return records that contain the terms red and car near one another, or contain the term cars - the link between red and cars we want might be lost. Parenthesis avoids this. To make sure the database does exactly what we want, you would use the string:
'red near (car or cars)'
Whilst parenthesis is a powerful tool you have to take care in the order of terms in search strings. Lets say we are interested in red cars or red automobiles. You might construct the search string:
'automobile and ( red or car)'
Unfortunately this will contain records containing the terms automobile and red, or the terms automobile and car, which is not quite what we want. The correct search string would be:
'red and (automobile or car)'
An incorrect search string is quite obvious when combining an adjective with nouns but with combinations purely of nouns you have to be more careful.
All this may seem very laborious, but using these search techniques is actually quick and easy once you have mastered them. In the longer run they will save you a great deal of of time and will make it easier to track down the information you need.