Querying Hyperset/Web-Like Databases

Hyperset approach to Web-like (semistructured) databases is presented in a simple and intuitive way, hopefully for a wider audience, with demonstrating how this abstract view can be represented in concrete terms of set equations distributed between many hyperlinked HTML files of a particular form. Detailed, bisimulation invariant operational semantics of hyperset query language Δ is defined by means of reduction rules transforming such systems of set equations. The high expressive power of this language, formerly characterised by using the technique of descriptive complexity theory, is illustrated by defining formal semantics of path expressions, as well as of other known languages UnQL and UnCAL. A “horizontal”, stronger alternative to structural recursion of UnCAL is introduced, both definable in Δ.