A GRAPH-REWRITING VISUAL LANGUAGE FOR DATABASE PROGRAMMING

Textual database programming languages are computationally complete, b ut have the disadvantage of giving the user a non-intuitive view of th e database information that is being manipulated. The visual languages developed in recent years have allowed naive users access to a direct representation of data, often in a graph form, but have concentrated on user interface rather than complex programming tasks. There is a ne ed for a system which combines the advantages of both these programmin g methods. We describe an implementation of Spider, an experimental vi sual database programming language aimed at programmers. It uses a gra ph-rewriting paradigm as a basis for a fully visual, computationally c omplete language. The graphs it rewrites represent the schema and inst ances of a database. The unique graph-rewriting method used by Spider has syntactic and semantic simplicity. Its form of algorithmic express ion allows complex computation to be easily represented in short progr ams. Furthermore, Spider has greater power than normally provided in t extual systems, and we show that queries an the schema and associative queries can be performed easily and without requiring any additions t o the language. (C) 1997 Academic Press Limited.