Visualization of Recursive Database-Query Output using a Declarative System: An Illustration through Parts-Assembly Tree Visualization

For visualization of output of database queries, the trial charts like bar graphs, line graphs, scatter plots and pie-charts are inappropriate even for small data set when the results of a query are generated recursively in the form of a graph or tree structure.Most of the recursive queries are used to retrieve hierarchical relationships among the instances of data within the database tables. Certain constraints are better represented by recursive rules. SQL 1999 standards allow the recursive queries using recursive common table expressions. To write these queries, views of relations have to be defined in terms of same table multiple times making procedural solutions less desirable. Datalog is also used for recursive queries.Since execution of most of the recursive queries can be represented by a syntax tree, therefore their output in most of the application scenarios is a tree. There is no support in SQL 1999 and Datalog to visualize output generated by recursive queries.In this research, the authors present visualization of output in two forms: First, an interactive tree view, and second, a complete non-interactive view of the output in the form of a tree.The correct results obtained from the system suggest that if software developers take care of appropriate ordering of the predicates, Prolog (PROgramming in LOGic) can be a better option over Datalog because Prolog provides many built-in predicates and many of its features make it suitable as a relational language.