31-05-2013, 12:28 PM
Location-Dependent Query Processing: Where We Are and Where We Are Heading
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ABSTRACT
The continuous development of wireless networks and mobile devices has motivated an intense
research in mobile data services. Some of these services provide the user with context-aware
information. Specifically, location-based services and location-dependent queries have attracted a
lot of interest.
In this article, the existing literature in the field of location-dependent query processing is reviewed.
The technological context (mobile computing) and support middleware (such as moving
object databases and data stream technology) are described, location-based services and locationdependent
queries are defined and classified, and different query processing approaches are reviewed
and compared.
INTRODUCTION
Nowadays, there is a great interest in mobile computing, motivated by an everincreasing
use of mobile devices, that aims at providing data access anywhere and
at anytime. These devices are used not only to make voice connections (e.g., mobile
phones) or to work locally (e.g., laptops, palmtops, etc.) but also to transmit
data. Indeed, several market forecasts predict a growth in the use of mobile data
services.
TECHNOLOGICAL CONTEXT: MOBILE COMPUTING
According to [Milojicic et al. 2000], in general two types of mobility can be distinguished:
software mobility and hardware mobility. Software mobility implies the
transfer of passive data (e.g., files) or active data (mobile code, process migration,
or mobile agents) [Carzaniga et al. 1997; Lange and Oshima 1999; Milojicic
et al. 2000] among computers. However, the survey presented in this article relates
to hardware mobility, which implies the physical mobility of mobile devices
while providing computing services anywhere and at anytime. This type of mobility
is located within the mobile computing framework, which “[...] no longer requires
users to maintain a fixed and universally known position in the network and enables
unrestricted mobility of the users” [Barbar´a 1999].
Challenges and Related Fields
In this section, we first present some challenges posed by mobile computing. The
focus is on data management issues. Therefore, other works concerning how to support
mobile computing on top of existing mobile environments, such as [Ioannidis
et al. 1991; Teraoka et al. 1991; Perkins and Bhagwat 1994; Perkins 1998], are not
considered here.
While mobile computing is expected to provide great economical benefits, it also
opens up new research issues for data management, due to the need for adapting
existing techniques to the mobile environment [Imielinski and Nath 1993; Alonso and Korth 1993; Forman and Zahorjan 1994; Imielinski 1996a; Pitoura and Samaras
1998; Barbar´a 1999]. Particularly, the concept of mobile databases, where the users
and/or data may be mobile, appears to highlight the differences with traditional
distributed database systems [¨Ozsu and Valduriez 1999]. An early characterization
of the new problems appeared in [Alonso and Korth 1993].