In a database missing values may be denoted by the use of a special null symbol. However, between the extremes of complete information and missing information one may have various states of incomplete or partial information. One of the advantages which logic databases will have over relational database is the ability to handle incomplete information in a more helpful way than simply through the use of null values. This paper considers three forms of incomplete information and describes how the query language Query-by-Example can be extended to cater for these forms. The implementation of these ideas in Prolog is described to illustrate how these concepts can be realised in a logic programming language.
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|Published - Apr 1988