Refresher Course: Boolean AND (Searching OR Retrieval)

By Morton, Douglas | Online, January 1993 | Go to article overview

Refresher Course: Boolean AND (Searching OR Retrieval)


Morton, Douglas, Online


Boolean operators are the basic tools, the hammers and saws, of most of the information retrieval systems we use today. The structure of those information systems has been shaped by the Boolean logical operators and, or, and not. From edge-punch cards and peek-a-boo card systems to online catalogs and even artificial intelligence systems, all have Boolean operations at their core.

The or operator is used to pull together database records with similar concepts (e.g., chipboard or plywood). The and operator is used to extract records with more than one idea in common (e.g., 2x4 studs and nails). The not operator eliminates articles containing unwanted words (e.g., siding not vinyl). As with any tools, you have to watch what you are doing; you can hammer your finger as easily as a nail.

WHY USE BOOLEAN OPERATORS?

Print indexes are pre-coordinated, and all the expected logical connections have been considered in creating the index entries. Print indexes are and operations already clone for you. When you look up alternate headings you are performing an or operation.

Most computerized database systems index each word as a separate item and the computer only retrieves the words you request. This kind of system gives you the freedom to create connections that the indexer did not make, but adds complexity to your life. You have to develop a "concept map" and use the Boolean operators to link its various sections. Concept mapping is the key to a good search. The Venn diagrams in Figure 1 will also help in understanding how to combine word concepts.

WHEN TO USE THEM

You are likely to use Boolean operators in every search. If you don't need them, ask yourself if you might be better off using the print index? The Boolean operators work best on databases with short records - when records contain long abstracts or full text it is time to brush up on proximity operators.

BOOLEAN BASICS

Because each system operates a little differently, get the manual for the system you use and read it. This article is dealing with Boolean searching in general, and your manual will fill in the finer points for your preferred system. System manuals give the details about Boolean operators under such chapter headings as "Combining Search Sets," Connectors," "Logical Operators," "Basic Search Logic," or "Modify Your Search."

Some operators will appear under different names, especially if you use a menu-driven system. Some may be hidden as part of filling in a worksheet; the system merely translates these into ANDs and ORs and proceeds with the search. Despite their disguises, they all do the same thing from system to system.

As you prepare for a search or interview a client, keep in mind that colloquial English does not use AND or OR with the same exactness that the computer will require. A client may specify interest in "oak and maple and birch and pine and spruce" when he really means "oak or maple or birch or pine or spruce" in Boolean language.

SYSTEM DEFAULTS

Some systems allow you to leave a space and the search will default to an or, an and, or a phrase. Unless you have a perfect memory, I recommend ignoring such defaults. The amount of time spent typing a few extra characters will be saved by not rerunning incorrect searches. In addition, you or your client will understand better what you are doing when everything is spelled out.

USING THE or OPERATOR

The computer retrieves exactly what it is told to find and nothing else - therefore, you have to instruct it to look for variations on your search words. To build individual words into a concept, you link synonymous words or phrases with or. The net effect will be to increase the number of references retrieved.

Using the or operator will retrieve a list of records in which at least one of the search words is required to be present.

Instructions about using the or operator can also appear in manuals and search instructions as the "union" of sets, or "broaden the search topic. …

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