Cloaking data to ease view creation, query expression, and query execution

XML schemas often allow many aspects of an object to be described in the same document, but queries over such documents might be concerned with just one aspect. For example, an XML representation of a spreadsheet can include both spreadsheet data and styling, but a query might address only the data portions. In these situations, traditional approaches first define a data-only view and then query that view. However, these approaches can make it hard to define views and to express queries; and in some cases (even with view unfolding), they can even make query-execution inefficient in terms of time and space. We propose cloaking document parts and selectively revealing the cloaked parts as an alternative. Cloaking exposes many simultaneous conceptual views of a document without constructing new data, allows queries to be expressed in existing languages, and it can be easily supported in existing query processors. In this paper, we present a formal model for cloaking, its application in a cloaking query processor, and the results of an experimental evaluation in the context of superimposed information (SI, information with references to existing information) and bi-level information (SI along with the referenced information). Our experiments suggest that cloaking can make it easier to define views and to express queries, and that for certain query classes, a cloaking query processor saves both time and memory when compared to a traditional query processor. © 2012 Springer-Verlag Berlin Heidelberg.