Implementation of the Visual Query Language CQL for Transitive Computation

AUTHORS and Kalervo Järvelin*, Timo Niemi# and Airi Salminen+

*Department of Information Studies
#Department of Computer Science
University of Tampere
P.O.Box 607
FIN-33101 TAMPERE, Finland

+Department of Computer Science and Information Systems
University of JyvŠskylŠ, P.O.Box 35
FIN-40351 JYV€SKYL€, Finland

University of Tampere, Department of Information Studies, Research Notes RN-1995-1

Abstract

CQL (Classification Query Language) is a high-level visual QBE-like query language with a great expressive power. The implementation of the language described in this paper is intented for data classification. In data classification, transitive relationships among classified data have an important role. The computation of transitive relationships is beyond the traditional data models. Recursion is a natural way of defining transitive relationships. The CQL language incorporates ordinary relations as well as hierarchical classifications. Relations and classifications are represented in the visual interface through relation and classification skeletons. All query formulation in the visual language is QBE-like, i.e. based on the intuitive way of filling constants and sample values into the skeletons. The use of relations and classifications is integrated seamlessly so that relational and classification expressions can be nested freely with each other without limiting nesting levels.

The visual language embeds recursion into concepts of classifications which can be interpreted as such in the application domain. Recursive definition is totally hidden from the users. Therefore users' query formulation in CQL is both easy and safe. The implementation of CQL is based on relational algebra and a set of direction-oriented operations on transitive relationships (e.g., multiple hierarchical classifications). Each direction-oriented operation can be performed among a collection of binary relations representing transitive relationships. The benefit of these operations is that the computation of the transitive closure of one large binary relation can be avoided. Both the direction of computation and subsets of the collection of binary relations have obvious semantic interpretations in many application domains. The translation process of visual CQL expressions into expressions of the operation-oriented query language is presented. CQL has been implemented on the basis of our experimental deductive database system which has been implemented in a homogeneous way. Also the implementation of CQL in the heterogeneous way is outlined.

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