A VISUAL QUERY LANGUAGE FOR GRAPHICAL INTERACTION WITH SCHEMA-INTENSIVE DATABASES

This paper presents a visual query language called VQL for interacting with an object-oriented schema-intensive data model. VQL allows conve nient access to the various types of knowledge captured by the semanti c model. It consists of a set of ''graphical primitives'' along with a combination grammar for creating graphical queries. The visual langua ge is internally supported by a prolog-like predicate based query lang uage. The formal grammar underlying the predicate based language is al so presented. Apart from being able to create simple queries that can be specified in SQL or QBE, VQL can be used for making queries on any object-oriented data model including the generalization of the E-R mod el. VQL also handles complicated, indirect queries, specially those th at require a reasoning system for query interpretation and response ge neration. Further, recursive queries on graph structures such as findi ng transitive closures of graphs may be easily specified. Perhaps the most powerful feature of VQL is its ability to provide high semantic e xpressibility (in being able to specify highly complex queries) while maintaining simplicity in the user's query formulation process. VQL is embedded in an object-oriented graphical database interaction environ ment that supports schema creation and manipulation in addition to dat abase querying and updation. The prototype has been implemented in Sma lltalk-80 running on a Sun 3/60 workstation. All the illustrations of visual interaction presented in this paper are taken from actual inter action sessions.