CQL: A QBE-like visual recursive query language.

Salminen, A.#, Järvelin, K.* & Niemi, T.+

#Department of Computer Science and Information Systems
University of Jyväskylä
P.O.Box 35
FIN-40351 JYVÄSKYLÄ, Finland

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

Jyväskylä, Finland: University of Jyväskylä, Dept. of Computer Science and Information Systems, Report WP-32, March 1995. 127 p.

Abstract

Data classification is an essential part in many database applications. In data classification, transitive relationships among classified data have an important role. The computation of transitive relationships is beyond the traditional data models because it presupposes the possibility of recursive definition. In this paper we develop a high-level visual QBE-like query language, called CQL (Classification Query Language), which is able to manipulate transitive relationships with minimal user effort. The language incorporates ordinary relations as well as hierarchical classifications which can be used transitively / recursively. Relations and classifications are represented in the visual interface through table and classification skeletons. All query formulation in the visual language is QBE-like, i.e. based on the intuitive way of inserting constant values and sample values into the skeletons. The use of tables and classifications is integrated seamlessly so that relational and classification expressions can be nested freely with each other without limiting nesting levels.

The abstraction level of the visual constructs of the language, tables and hierarchical classifications, is high and their interpretation is obvious in many application domains. 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 the visual language is both easy and safe.

The interpretation of CQL expressions into the internal intermediate representation is described and the translation of the intermediate expressions into the expressions of a textual, operation-oriented query language is defined. The proposed visual query language has been implemented in the homogeneous approach in our experimental Prolog-based deductive database system. The implementation of CQL in the heterogeneous approach in relational database environments is also discussed.

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