OR and NOR Searches
OR is a logic operation whose output is true when all or at least one of its inputs is true. When followed by NOT the result is NOR, its logical complement.
Applications to IR
An OR operation can be applied to information retrieval problems (1 - 3). For instance, including OR in a query instructs a search engine to match any of the search terms. In Minerazzi, OR is declared at the beginning of a search, like this
OR:w1 w2 w3(1)
This query matches documents containing w1, w2, w3, w1 w2, w1 w3, w2 w3, w1 w2 w3 in any order or proximity.
The following figure illustrates this search.
The colored region represents the subsets of documents matching this search (OR matches). The white region, labeled as an empty subset { } represents the number of documents matching none of the search terms. These are called NOR "matches" because are returned when the NOR operator is used, like this
NOR:w1 w2 w3(2)
Applications
OR presumes that terms are completely independent from each others; that is, it makes no assumption about term relationships or about their proximity and ordering in documents and queries. Thus, a search like [ OR:marketing research ] returns documents matching marketing, research, or marketing research in any order or proximity.
Because of its nature, OR broadens a search at the expense of returning many irrelevant results. Sometimes including synonyms and related terms in an OR search helps to improve the relevancy of the results.
Final Remarks
Minerazzi supports the OR search mode and its complement. This mode helps users to broaden their searches. Because of its nature, it can return many irrelevant results.
References
- Australasian Legal Information Institute (Accessed on 1-1-2014). Search Operators Chart.
- University of Reading (Accessed on 1-1-2014). Search Techniques.
- Case Western Reserve University, Harris Library (Accessed on 1-1-2014). Harris Library Boolean Logic Tutorial.