Introduction - Repairing and Querying Databases under Aggregate Constraints - page 11

considered in this topic was introduced in [22], where the complexity of several
problems regarding the extraction of reliable information from inconsistent numer-
ical data (i.e. repair existence, minimal repair checking, as well as consistent query
answer) was investigated. In [25] the problem of repairing and querying database
inconsistent w.r.t. aggregate constraints was further investigated. In [21], the ar-
chitecture of a tool for acquiring and repairing numerical data inconsistent w.r.t.
a restricted form of aggregate constraints was presented, along with a strategy for
computing reasonable repairs, whereas in [23] the problem of computing reason-
able repairs w.r.t. a set of both strong and weak aggregate constraints was addressed.
The problem of querying inconsistent numerical databases was further investigated
in [24, 27], where techniques for evaluating aggregate queries were presented.
1.4 Organization
This topic provides an overview of the research done in the context of repairing
and querying databases inconsistent w.r.t. a given set of aggregate constraints. The
manuscript is organized as follows. In Chapter 2, the notion of repair as consistent
set of updates at attribute-value level, as well as that of consistent query answer is
defined. This notions are then exploited in Chapter 3, where the characterization of
several data-complexity issues related to repairing data and computing consistent
query answers is provided. Next, in Chapter 4 a method for computing reasonable
repairs of inconsistent numerical databases is introduced, for a restricted but ex-
pressive class of aggregate constraints, namely steady aggregate constraints .An
extension of this method for dealing with the data repairing problem in the pres-
ence of aggregate constraints with weak semantics is also presented. In Chapter 5,
a technique for computing consistent answers of aggregate queries in the presence
of steady aggregate constraints is presented. Many of the results presented in Chap-
ter 3, 4 and 5 can be studied in depth in [22, 21, 23, 25, 24, 27]. Finally, extensions
of the framework as well as several open problems are discussed in Chapther 6.