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Structural Queries

Beeri and Kornatzky have suggested a logical query language that would allow structural queries over a hypertext network. First-order logic is too general since it ignores the particular characteristics of hypertext. Hence, there is a need for a structural query language to incorporate the notions of recursive and quantification constructs. The logic for the proposed query language is a mixture of propositional calculus (which has no predicates or variables) and quantifiers such as many, most, at least two, exactly five etc. [Beeri & Kornatzky, 1990]. The basic formulae of the logic are the propositions and assertions on attributes' values. Queries use specifiers to directly retrieve edges, paths, and cycles. The set of elements retrieved is collapsed into a hypertext network. The output of a query being a hypertext network, users can incrementally compose queries. Thus, the combination of specifiers, quantifiers, and the collapsing of query answers into a new hypertext network makes it possible to express structural queries proposed by Halasz. Facilities also exist in this query language to view portions of the retrieved network based on the specification of filters. Research is also underway to develop a visual hypertext query language.