Query by Browsing (QBB) is a relationally complete paradigm for creating Visual Query Language (VQL)s. It has been adapted successfully for use on handheld devices in the form of the Chiromancer interface, thus placing considerable search capabilities at the fingertips of mobile users. In this paper we describe an enhancement to the QBB paradigm to accommodate continuous queries through the use of active folders, i.e. folders whose contents are constantly updated. We thus demonstrate how such continuous queries coupled with a suitable context-describing database schema can be used to support a variety of context-aware application scenarios. A prototype architecture and context schema are described as are the extensions to the QBB paradigm and the additions to the Chiromancer interface needed to support these scenarios.

In this paper we introduce and formally define Query by Browsing (QBB), a scalable, relationally complete visual query language based on the desktop user interface paradigm and tuple relational calculus that allows the formulation of complex queries over relational, entity-relationship, object-oriented and XML data sources on a variety of handheld and desktop platforms. It is to our knowledge the first visual query language to combine the important characteristics of usability, scalability, expressive power and flexibility. We support these claims by demonstrating the similarity of the QBB paradigm to the popular desktop user interface paradigm, by relating it to relational calculus and relational algebra and by describing Chiromancer II, a Web-based implementation of the QBB paradigm for handheld devices. We also discuss ways in which non-relational sources can be represented and queried and compare QBB to related work in the area of visual query languages for a variety of data models. We finally offer conclusions and thoughts for future work.