In this paper, we present the design and implementation of a graphical user interface to interact with a relational database management system on touch screen based mobile devices. Our system allows users to author arbitrary graphical relational queries on the touch screen using a collection of on-screen widgets and gestures. The user can interact, introspect and integrate pieces of sub-queries on the mobile device. The system dynamically performs type checking during the authoring, so the user receives immediate visual feedback in case of semantic error in the resulting query. We have deployed our system on several Android devices ranging from the 4" smart phones to 7" and 10" tablets. Our usability study shows that our query interface, provides a significant improvement in the user experience when querying a relational data model. The system allows fast authoring speed of complex queries, and user friendly experience.
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