A state of art survey on zz-structures

Zz-structures are particular data structures capable of representing both hypertextual information and contextual interconnections among different information. The focus of this paper is to stimulate new research on this topic, by providing, in a state of the art survey, a short description and comparison of all the material that, to the best of our knowledge, is related to zz-structures: informal and formal descriptions, implementations, languages, demonstrations, projects and applitudes of zz-structures; in fact, despite their large use in different fields, the literature lacks of an exhaustive and up-to-date description of them.