The Role of Quasi-identifiers in k-Anonymity Revisited

The concept of k-anonymity, used in the recent literature to formally evaluate the privacy preservation of published tables, was introduced based on the notion of quasi-identifiers (or QI for short). The process of obtaining k-anonymity for a given private table is first to recognize the QIs in the table, and then to anonymize the QI values, the latter being called k-anonymization. While k-anonymization is usually rigorously validated by the authors, the definition of QI remains mostly informal, and different authors seem to have different interpretations of the concept of QI. The purpose of this paper is to provide a formal underpinning of QI and examine the correctness and incorrectness of various interpretations of QI in our formal framework. We observe that in cases where the concept has been used correctly, its application has been conservative; this note provides a formal understanding of the conservative nature in such cases.Comment: 17 pages. Submitted for publicatio

Lossless outer joins of relations containing nulls

Information is often incomplete in databases, and nulls are required to represent missing or unknown data; however, many difficulties occur with nulls. In his 1983 text, C. J . Date rejected outer join of relations with nulls mainly due to a perceived problem with functional dependencies (FDs): when nulls are present in R, outer join does not seem to support the lossless normalizations cased on Rissanen's Theorem. Alternatively, we show here that if care is taken to join the relations along common attributes that "tuple-connect" them, which we argue is reasonable, then appropriate analogues of Rissanen's Theorem hold, for null-valued FDs, and NMVDs, using extended outer Join. These results tend to rehabilitate the usefulness of outer join for forming universal relations with nulls

An algebraic representation of calendars.

This paper uses an algebraic approach to define temporal granularities and calendars. All the granularities in a calendar are expressed as algebraic expressions based on a single "bottom" granularity. The operations used in the algebra directly reflect the ways with which people construct new granularities from existing ones, and hence yield more natural and compact granularities definitions. Calendar is formalized on the basis of the algebraic operations, and properties of calendars are studied. As a step towards practical applications, the paper also presents algorithms for granule conversions between granularities in a calendar