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Boolean Search Rules

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A number of the other search engines have search programs similar to Google. Many, like Google, utilize a Boolean retrieval method. Boolean retrieval is one of the simplest and oldest retrieval methods and uses an exact matching concept.

Documents on file, or in a search engine's case - indexed, are exactly matched to a document representing a user query.

Boolean refers to Boolean algebra where keywords are combined with the Boolean operators of AND, OR, and NOT to form logical statements.

In the case where none of the three terms - AND, OR, or NOT - are entered within the query - Google assumes that the AND is operative. This is known as the default setting.

The Boolean model operates by determining which keywords are present or absent in a document. Based on this determination the document is deemed relevant or irrelevant to the query.

The search engine then takes the relevant documents and ranks the relevance of each based on its internal algorithm. The results are then presented to the user in relevance order - from high to low.

It is likely that Google gives a certain amount of preference if the keywords are located in a heading, url, or title - places deemed to contain important words regarding the page. And preference is also likely accorded if there is significant frequency of the keywords.

Why is Boolean Used?

Many search engines , including Google, use a Boolean model as the basis for satisfying a searchers request for information. The reasons for this are fairly straight-forward.

First, Boolean reduces the query down to simple logic of yes or no. Is the keyword present or is it absent? Does the Boolean operation indicate that every keyword be present or either one or not at all? It is black and white - easy to understand - easy to explain.

Second, since the logic is so simple - it is relatively easy to program.

Third, queries can be satisfied quickly. Parallel scans can be made through the documents for the keywords.

Fourth, Boolean is not affected by larger volumes of documents, queries or keywords. As the internet grows, the programming remains simple. Only the data storage and parallel search capabilities need to be upgraded.

In the next section we will examine Boolean further.

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