Chapter 10: User Interfaces and Visualization
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Modern Information Retrieval Chapter 10: User Interfaces and Visualization |
Contents |
In modern information access systems the matching process usually employs a statistical ranking algorithm. However, until recently most commercial full-text systems and most bibliographic systems supported only Boolean queries. Thus the focus of many information access studies has been on the problems users have in specifying Boolean queries. Unfortunately, studies have shown time and again that most users have great difficulty specifying queries in Boolean format and often misjudge what the results will be [#!boyle84!#,#!greene90!#,#!michard82!#,#!young93!#].
Boolean query specification!problems with syntax
Boolean queries are problematic for several reasons. Foremost among these is that most people find the basic syntax counter-intuitive. Many English-speaking users assume everyday semantics are associated with Boolean operators when expressed using the English words AND and OR, rather than their logical equivalents. To inexperienced users, using AND implies the widening of the scope of the query, because more kinds of information are being requested. For instance, `dogs and cats' may imply a request for documents about dogs and documents about cats, rather than documents about both topics at once. `Tea or coffee' can imply a mutually exclusive choice in everyday language. This kind of conceptual problem is well documented [#!boyle84!#,#!greene90!#,#!michard82!#,#!young93!#]. In addition, most query languages that incorporate Boolean operators also require the user to specify complex syntax for other kinds of connectors and for descriptive metadata. Most users are not familiar with the use of parentheses for nested evaluation, nor with the notions associated with operator precedence.
By serving a massive audience possessing little query-specification experience, the designers of World Wide Web search engines have had to come up with more intuitive approaches to query specification. Rather than forcing users to specify complex combinations of ANDs and ORs, they allow users to choose from a selection of common simple ways of combining query terms, including `all the words' (place all terms in a conjunction) and `any of the words' (place all terms in a disjunction).
Another Web-based solution is to allow syntactically-based query specification, but to provide a simpler or more intuitive syntax. The `+' prefix operator gained widespread use with the advent of its use as a mandatory specifier in the Altavista Web search engine. Unfortunately, users can be misled to think it is an infix AND rather than a prefix mandatory operator, and thus assume that `cat + dog' will only retrieve articles containing both terms (where in fact this query requires dog but allows cat to be optional).
Another problem with pure Boolean systems is they do not rank the retrieved documents according to their degree of match to the query. In the pure Boolean framework a document either satisfies the query or it does not. Commercial systems usually resort to ordering documents according to some kind of descriptive metadata, usually in reverse chronological order. (Since these systems usually index timely data corresponding to newspaper and news wires, date of publication is often one of the most salient features of the document.) Web-based systems usually rank order the results of Boolean queries using statistical algorithms and Web-specific heuristics.