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Comprehensive List of Researchers "Information Knowledge"

Department of Information Engineering

Software Science and Technology Group
Assistant Professor
Dr. of Information Science
Research Field
Formal language theory / Formal verification
SEKI, Hiroyuki

Current Research

Verification of transformations on structured data

Tree and graph structured data, such as XML and RDF, are widely used in recent years. For transformations on such structured data, we study formalization of the following properties and how to verify formally whether the properties are satisfied or not.

(1) Information preservation
In data transformation, it is desirable that certain information in source data be preserved through transformation. However, there is a trade-off between conditionality of information preservation and flexibility of designs of transformations. Query preservation is known as one of formalizations for information preservation. Intuitively, query preservation means that any information obtained by the query to the source data can be extracted from the transformed data by some query. By specifying appropriate queries as parameters, query preservation can be a sensible condition for information preservation on transformations. The verification of query preservation is an important problem, but it is undecidable in general. In our research, we find for which classes of transformations on structured data query preservation is decidable, and formulate a verification method.

(2) Tolerance to inference attacks
For a database system to be secure, secrecy, integrity, and availability of data must be achieved appropriately with respect to a given security policy. View mechanisms have played a principal role in achieving the secrecy of database systems. Views (or transformations) can avoid direct accesses to sensitive information in the database. However, there still is a possibility of indirect accesses, i.e., the sensitive information can be inferred using authorized views and/or general domain knowledge. To measure such risk, metrics for safety against inference attacks is needed. Currently, we adopt k-secrecy as the metrics. The underlying concept of k-secrecy is that it can be considered to be insecure that the set of candidates for the value of the sensitive information can be narrowed down by inference. We are studying methods that checks whether data (and views) satisfy k-secrecy or not.


  • Kenji Hashimoto received the Doctor of Information Science degree from Osaka University in March 2009.
  • He became an assistant professor of Nara Institute of Science and Technology in April 2009.
  • He has been an assistant professor of Nagoya University since October 2013.

Academic Societies

  • IPSJ


  1. C. Phonharath, K. Hashimoto, and H. Seki, ``Deciding Schema k-Secrecy for XML Databases,'' IEICE Transactions on Information and Systems, Vol. E96-D, No. 6, pp. 1268-1277, 2013.
  2. K. Miyahara, K. Hashimoto, and H. Seki, ``Node Query Preservation for Deterministic Linear Top-Down Tree Transducers,'' In Proc. of TTATT 2013, Vol. 134, pp. 27-37, 2013.
  3. Y. Ishihara, N. Suzuki, K. Hashimoto, S. Shimizu, and T. Fujiwara, ``XPath Satisfiability with Parent Axes or Qualifiers Is Tractable under Many of Real-World DTDs,'' In Proc. of DBPL 2013,, 2013.
  4. H. Kuwada, K. Hashimoto, Y. Ishihara, and T. Fujiwara, ``The Consistency and Absolute Consistency Problems of XML Schema Mappings between Restricted DTDs,'' In Proc. of APWeb 2013, pp. 228-239, 2013.
  5. K. Hashimoto, R. Sawada, Y. Ishihara, H. Seki, and T. Fujiwara, ``Determinacy and Subsumption for Single-valued Bottom-up Tree Transducers,'' In Proc. of LATA 2013, pp. 335-346, 2013.