ABSTRACT
The notion of certain answers arises when one queries incompletely specified databases, e.g., in data integration and exchange scenarios, or databases with missing information. While in the relational case this notion is well understood, there is no natural analog of it for XML queries that return documents.
We develop an approach to defining certain answers for such XML queries, and apply it in the settings of incomplete information and XML data exchange. We first revisit the relational case, and show how to present the key concepts related to certain answers in a new model-theoretic language. This new approach naturally extends to XML. We prove a number of generic, application-independent results about computability and complexity of certain answers produced by it. We then turn our attention to a pattern-based XML query language with trees as outputs, and present a technique for computing certain answers that relies on the notion of a basis of a set of trees. We show how to compute such bases for documents with nulls and for documents arising in data exchange scenarios, and provide complexity bounds. While in general complexity of query answering in XML data exchange could be high, we exhibit a natural class of XML schema mappings for which not only query answering, but also many static analysis problems can be solved efficiently.
- S. Abiteboul, R. Hull, and V. Vianu. Foundations of Databases. Addison-Wesley, 1995. Google Scholar
Digital Library
- S. Abiteboul, P Kanellakis, and G. Grahne. On the representation and querying of sets of possible worlds. TCS, 78(1):158--187, 1991. Google Scholar
Digital Library
- S. Abiteboul, L. Segoufin, and V. Vianu. Representing and querying XML with incomplete information. ACM TODS, 31(1):208--254, 2006. Google Scholar
Digital Library
- S. Amano, Claire David, L. Libkin, and F. Murlak. On the tradeoff between mapping and querying power in XML data exchange. In ICDT'10, to appear. Google Scholar
Digital Library
- S. Amano, L. Libkin, and F. Murlak. XML schema mappings. In PODS'09, pages 33--42. Google Scholar
Digital Library
- M. Arenas and L. Libkin. XML data exchange: consistency and query answering. J. ACM, 55(2), 2008. Google Scholar
Digital Library
- D. Barbosa, L. Mignet, P. Veltri. Studying the XML web: gathering statistics from an XML sample. WWW 9(2):187--212 (2006). Google Scholar
Digital Library
- P. Barcelo. Logical foundations of relational data exchange. SIGMOD Record, 38(1):49--58, 2009. Google Scholar
Digital Library
- P. Barcelo, L. Libkin, A. Poggi, and C. Sirangelo. XML with incomplete information: models, properties, and query answering. In PODS'09, pages 237--246. Google Scholar
Digital Library
- P. Bernstein and S. Melnik. Model management 2.0: manipulating richer mappings. In SIGMOD'07, pages 1--12. Google Scholar
Digital Library
- H. Bjorklund, W. Martens, and T. Schwentick. Conjunctive query containment over trees. In DBPL'07, pages 66--80. Google Scholar
Digital Library
- H. Bjorklund, W. Martens, and T. Schwentick. Optimizing conjunctive queries over trees using schema information. In MFCS'08, pages 132--143. Google Scholar
Digital Library
- P. Buneman, L. Libkin, D. Suciu, V. Tannen, and L. Wong. Comprehension syntax. SIGMOD Record, 23(1):87--96, 1994. Google Scholar
Digital Library
- A. Cali, D. Lembo, and R. Rosati. On the decidability and complexity of query answering over inconsistent and incomplete databases. In PODS'03, pages 260--271. Google Scholar
Digital Library
- D. Calvanese, G. De Giacomo, and M. Lenzerini. Representing and reasoning on XML documents: A description logic approach. J. Logic & Comput., 9(3):295--318, 1999.Google Scholar
Cross Ref
- D. Calvanese, G. De Giacomo, M. Lenzerini, and M. Y. Vardi. Regular XPath: constraints, query containment and view-based answering for XML documents. In LID'08, 2008.Google Scholar
- A. Chandra and P. Merlin. Optimal implementation of conjunctive queries in relational data bases. In STOC'77, pages 77--90. Google Scholar
Digital Library
- A. Deutsch and V. Tannen. XML queries and constraints, containment and reformulation. TCS, 336(1): 57--87, 2005. Google Scholar
Digital Library
- R. Fagin, Ph. Kolaitis, R. Miller, and L. Popa. Data exchange: Semantics and query answering. TCS, 336(1):89--124, 2005. Google Scholar
Digital Library
- R. Fagin, Ph. Kolaitis, and L. Popa. Data exchange: getting to the core. ACM TODS, 30(1):174--210, 2005. Google Scholar
Digital Library
- R. Fagin, Ph. Kolaitis, L. Popa, and Wang Chiew Tan. Composing schema mappings: second-order dependencies to the rescue. ACM TODS, 30(4):994--1055, 2005. Google Scholar
Digital Library
- S. Flesca, F. Furfaro, S. Greco, and E. Zumpano. Repairs and consistent answers for XML data with functional dependencies. In XSym'03, pages 238--253.Google Scholar
- G. Gottlob, C. Koch, and K. Schulz. Conjunctive queries over trees. J. ACM 53(2):238--272, 2006. Google Scholar
Digital Library
- G. Grahne. The Problem of Incomplete Information in Relational Databases, Springer, 1991. Google Scholar
Digital Library
- C. Gutierrez, C. Hurtado, and A. Mendelzon. Foundations of semantic web databases. In PODS'04, pages 95--106. Google Scholar
Digital Library
- P. Hell and J. Nesetril. The core of a graph. Discrete Math., 109(1-3):117--126, 1992. Google Scholar
Digital Library
- T. Imielinski and W. Lipski. Incomplete information in relational databases. J. ACM, 31(4):761--791, 1984. Google Scholar
Digital Library
- B. Kimelfeld and Y. Sagiv. Matching twigs in probabilistic XML. In VLDB'07, pages 27--38. Google Scholar
Digital Library
- B. Kimelfeld and Y. Sagiv. Modeling and querying probabilistic XML data. SIGMOD Record, 37(4):69--77, 2008. Google Scholar
Digital Library
- Ph. Kolaitis. Schema mappings, data exchange, and metadata management. In PODS'05, pages 61--75. Google Scholar
Digital Library
- L. Popa, Y. Velegrakis, R. Miller, M. Hernandez, and R. Fagin. Translating web data. In VLDB'02, pages 598--609. Google Scholar
Digital Library
- R. Reiter. Towards a logical reconstruction of relational database theory. In On Conceptual Modelling, Springer, pages 191--233, 1982.Google Scholar
- R. Reiter. A sound and sometimes complete query evaluation algorithm for relational databases with null values. J. ACM 33(2):349--370, 1986. Google Scholar
Digital Library
- W3C. XQuery, W3C Recommendation. available at http://www.w3.org/TR/xquery, 2007.Google Scholar
- P. Wadler. Comprehending monads. Math. Str. in Comp. Sci., 2(4):461--493, 1992.Google Scholar
Cross Ref
- L. Wong. Kleisli, a functional query system. J. Funct. Program., 10(1):19--56, 2000. Google Scholar
Digital Library
- C. Yu and L. Popa. Constraint-based XML query rewriting for data integration. In SIGMOD'04, pages 371--382. Google Scholar
Digital Library
Index Terms
Certain answers for XML queries
Recommendations
XML Schema Mappings: Data Exchange and Metadata Management
Relational schema mappings have been extensively studied in connection with data integration and exchange problems, but mappings between XML schemas have not received the same amount of attention. Our goal is to develop a theory of expressive XML schema ...
Describing and deriving certain answers over partial databases
Although there has been much work in recent years on answering queries using views, there has been less work on deriving answers from partial databases. That is given a partial database state DV, materialized via the view V, what queries can be asked ...
View-based query answering in Description Logics: Semantics and complexity
View-based query answering is the problem of answering a query based only on the precomputed answers to a set of views. While this problem has been widely investigated in databases, it is largely unexplored in the context of Description Logic ...






Comments