Recursion with the Graphical Query Language Candid

Abstract

CANDID is a graphical interface for data base manipulation designed for the final user. It is based on a generic semantic model using attributes and constructors. Each schema is represented by a graph where the nodes are associated to different object types and where the edges represent relationships between types. The graphical query language makes it possible to express a request by describing with a graph an object solution of the request. Specifying a request means the same as defining derived elements that can be incorporated definitively into the schema. This language is also characterized by the absence of boolean operators and quantifiers which are replaced by manipulations on Venn diagrams. This article shows how recursive requests can be expressed in CANDID through a tree-structure constructor.