09-02-2013, 12:32 PM
A Survey of Context Data Distribution for Mobile Ubiquitous Systems
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ABSTRACT
The capacity to gather and timely deliver to the service level any relevant information that can characterize
the service-provisioning environment, such as computing resources/capabilities, physical device location,
user preferences, and time constraints, usually defined as context-awareness, is widely recognized as
a core function for the development of modern ubiquitous and mobile systems. Much work has been
done to enable context-awareness and to ease the diffusion of context-aware services; at the same time,
several middleware solutions have been designed to transparently implement context management and
provisioning in the mobile system. However, to the best of our knowledge, an in-depth analysis of the
context data distribution, namely, the function in charge of distributing context data to interested entities,
is still missing. Starting from the core assumption that only effective and efficient context data distribution
can pave the way to the deployment of truly context-aware services, this article aims at putting together
current research efforts to derive an original and holistic view of the existing literature. We present a
unified architectural model and a new taxonomy for context data distribution by considering and comparing
a large number of solutions. Finally, based on our analysis, we draw some of the research challenges still
unsolved and identify some possible directions for future work.
INTRODUCTION
The popularity of wireless devices and the increasing availability of heterogeneous
wireless infrastructures, spanning from IEEE 802.11 and Bluetooth to cellular 3G
and beyond, are stimulating new service provisioning scenarios. A growing number of
users require access anytime and anywhere to their Internet services, such as email,
printing, Voice over IP, social computing, and others, while moving across different
wireless infrastructures. In the so called Internet of Things vision, mobile users will be
able to dynamically discover and interact with heterogeneous computing and physical resources encountered during their roaming on an impromptu basis [Gershenfeld et al.
2004].
CONTEXT AND CONTEXT DATA DISTRIBUTION
Context-awareness has now a very wide meaning, and it can be considered even a
contradictory word that may express several and different senses, according to the
specific scenario and author. Since there is no agreed upon definition, the next sections
settle required terminology and definitions. The aim of these sections is also to motivate
and to better point out the scope of this work.
Context and QoC Definition
Context is still a vague concept for identifying the aspects the designer considers
useful for modeling and for describing the environment in which a given service is
to be deployed and executed. Many authors present their own definition of context.
In Schilit et al. [1994], service context contains information addressing “where you
are, who you are with, and what resources are nearby.” In Dey and Abowd [2000a], it
contains “any information that can be used to characterize the situation of an entity.”
In Zimmermann et al. [2007], it comprises “elements for the description of this context
information [that] fall into five categories: individually, activity, location, time, and
relations.” In a common sense meaning, context is the “set of variables that may be of
interest for an agent and that influence its actions” [Bolchini et al. 2009].
Context Data Distribution in Mobile Ubiquitous Environments
Even if context-aware solutions have appeared in different research areas, contextawareness
reaches its maximum usefulness when applied to mobile ubiquitous systems.
Context-awareness permits mobile services to dynamically and efficiently adapt
both to the current situation, such as current physical place and/or social activity, and
to the challenging and highly variable deployment conditions typical of mobile environments
(e.g., resources scarcity, unreliable and intermittent wireless connectivity,
etc.). The central role of context data distribution in mobile computing is evidenced
also by the plethora of research efforts proposed in the last few years in this area.
Therefore, we have decided to focus on mobile ubiquitous systems to provide privileged
examples of context-aware systems. At the same time, we believe that the taxonomy
and analysis of context data distribution systems proposed here also apply to other
context-aware solutions in different research areas (such as fixed Internet services
computing, distributed database management systems, etc.).