Database Reference
In-Depth Information
Chapter 1
Introduction
Uncertain data is inherent in several important applications such as sensor network
management [1] and data integration [2], due to factors such as data randomness
and incompleteness, limitations of measuring equipment and delayed data updates.
Because of the importance of those applications and the rapidly increasing amount
of uncertain data, analyzing large collections of uncertain data has become an im-
portant task.
Ranking queries (also known as top- k queries) [3, 4, 5, 6] are a class of important
queries in data analysis. Although ranking queries have been studied extensively in
the database research community, uncertainty in data poses unique challenges on
the semantics and processing of ranking queries. Traditional queries and evaluation
methods on certain data cannot be directly adopted to uncertain data processing.
Therefore, practically meaningful ranking queries as well as efficient and scalable
query evaluation methods are highly desirable for effective uncertain data analysis.
1.1 Motivation
Recently, there have been an increasing number of studies on uncertain data man-
agement and processing [7, 8, 9, 10, 11, 12, 13, 14, 15, 16]. For example, the prob-
abilistic database model [7, 17, 8] and the uncertain object model [18, 19, 20, 21]
are developed to describe the uncertainty in data. More details about those models
can be found in Chapter 3. In some important application scenarios, various ranking
queries can provide intersecting insights into uncertain data.
Example 1.1 (Ranking queries in traffic monitoring applications). Roadside sensors
are often used to measure traffic volumes, measure vehicle speeds, or classify ve-
hicles. However, data collected from sensors as such cannot be accurate all the
time due to the limitations of equipment and delay or loss in data transfer. There-
fore, confidence values are often assigned to such data, based on the specific sensor
characteristics, the predicted value, and the physical limitations of the system [22].
1
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