Towards a unified visual database access

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Abstract
Since the development of QBE, over fifty visual query languages have been proposed to facilitate easy database access. Although these languages have introduced some very useful paradigms, a number of these have some severe limitations, such as: (a) not extending beyond the relational model (b) not considering negation and safety, formally (c) using ad hoc constructs, with no analysis of expressivity or complexity done, etc. Note that visual database access is an important issue being revisted, with the emergence of different flavors of object-oriented databases. We believe that there is a need for developing a unified visual query language. Specifically, our goal is to develop a visual query language that has the following properties: (i) It has a few core constructs using which “expert-users” can define new ( derived ) constructs easily (ii) “Normal users” can use easily either the core or the derived constructs for database querying (iii) It can implement representative constructs of other (textual or visual) query language straightforwardly, and (iv) It has formal semantics, with its theoretical properties, such as complexity, analyzed. We believe that we make a first step towards the above goal by introducing a new logical construct called restricted universal quantifier and combining it with the hierarchical structure of windows to develop a V isual Q uery L anguage, called VQL. The core constructs of VQL can encode easily a number of representative constructs of different (about six visual and four non-visual) relational, nested and object-oriented query languages. We also study the theoretical aspects such as safety, complexity, etc., of VQL.

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