On the complexity of query answering over incomplete XML documents

Previous studies of incomplete XML documents have identified three main sources of incompleteness – in structural information, data values, and labeling – and addressed data complexity of answering analogs of unions of conjunctive queries under the open world assumption. It is known that structural incompleteness leads to intractability, while incompleteness in data values and labeling still permits efficient computation of certain answers. The goal of this paper is to provide a complete picture of the complexity of query answering over incomplete XML documents. We look at more expressive languages, at other semantic assumptions, and at both data and combined complexity of query answering, to see whether some well-behaving tractable classes have been missed. To incorporate non-positive features into query languages, we look at gentle ways of introducing negation via inequalities and/or Boolean combinations of positive queries, as well as the analog of relational calculus. We also...

• Type: Journal
• Year: 2012
• Where: ICDT
• Authors: Amélie Gheerbrant, Leonid Libkin, Tony Tan
• Keywords: Boolean Combinations, Database, Evaluation Algorithms, ICDT 2012, World Assumption