2 research outputs found
Obtaining Information about Queries behind Views and Dependencies
We consider the problems of finding and determining certain query answers and
of determining containment between queries; each problem is formulated in
presence of materialized views and dependencies under the closed-world
assumption. We show a tight relationship between the problems in this setting.
Further, we introduce algorithms for solving each problem for those inputs
where all the queries and views are conjunctive, and the dependencies are
embedded weakly acyclic. We also determine the complexity of each problem under
the security-relevant complexity measure introduced by Zhang and Mendelzon in
2005. The problems studied in this paper are fundamental in ensuring correct
specification of database access-control policies, in particular in case of
fine-grained access control. Our approaches can also be applied in the areas of
inference control, secure data publishing, and database auditing
Assessing Achievability of Queries and Constraints
Assessing and improving the quality of data in data-intensive systems are
fundamental challenges that have given rise to numerous applications targeting
transformation and cleaning of data. However, while schema design, data
cleaning, and data migration are nowadays reasonably well understood in
isolation, not much attention has been given to the interplay between the tools
that address issues in these areas. Our focus is on the problem of determining
whether there exist sequences of data-transforming procedures that, when
applied to the (untransformed) input data, would yield data satisfying the
conditions required for performing the task in question. Our goal is to develop
a framework that would address this problem, starting with the relational
setting.
In this paper we abstract data-processing tools as black-box procedures. This
abstraction describes procedures by a specification of which parts of the
database might be modified by the procedure, as well as by the constraints that
specify the required states of the database before and after applying the
procedure. We then proceed to study fundamental algorithmic questions arising
in this context, such as understanding when one can guarantee that sequences of
procedures apply to original or transformed data, when they succeed at
improving the data, and when knowledge bases can represent the outcomes of
procedures. Finally, we turn to the problem of determining whether the
application of a sequence of procedures to a database results in the
satisfaction of properties specified by either queries or constraints. We show
that this problem is decidable for some broad and realistic classes of
procedures and properties, even when procedures are allowed to alter the schema
of instances