If you search a catalog or database and receive a large number of results, add a limit or additional keyword in order to retrieve a manageable and relevant number of results to review. At the same time overly narrow search terms can return too few results. One way of solving both problems is to use Boolean operators (AND, OR, NOT), which allow you to limit or expand searches depending on your needs.
For example, a search for oil AND politics will return items that contain both concepts":
petroleum OR oil returns items that contain either one of the terms or both:
central america NOT costa rica returns items that talk about the region but do not mention the country Costa Rica:
An important strategy to use when searching for phrases ("oil industry") or titles:
For example, "oil causes war"
will search for those words in that order, finding the 2013 book: Petro-aggression: when oil causes war by Jeff Colgan
Truncation and Wildcards:
Most catalogs and databases enable users to search variations of keywords by using truncation (*) or wildcard (e.g., ?, $, !) symbols.
For example, one could search for politic* to find poltic, politics, political, politicking, and so on.
Wildcard searches are for differences within words: a search for wom?n will return results for woman, women, and womyn.
When pairing two or more keywords with another keyword, it is important to "nest" the former terms within a larger Boolean search.
For example, (petroleum OR oil) (politic* OR war OR violen*) = 256 results
The search returns results for the union of the two subject areas.