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Challenges in Ubiquitous Data Management
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Improved hardware and networking are clearly central to the development of
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ubiquitous computing, but an equally important and difficult set of challenges revolve
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around Data Management [AK93]. In order for computing to fade into the
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background while supporting more and more activities, the data required to support
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those activities must be reliably and efficiently stored, queried, and delivered.
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Traditional approaches to data management such as caching, concurrency control,
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query processing, etc. need to be adapted to the requirements and restrictions of
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ubiquitous computing environments. These include resource limitations, varying and
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intermittent connectivity, mobile users, and dynamic collaborations.
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In this paper we first discuss the main characteristics of applications that
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ubiquitous computing aims to support and then focus on the requirements that such
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applications impose on data management technology. We then examine several
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different aspects of data management and how they are being adapted to these new
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requirements.
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Applications and Data Management Requirements
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While there is wide agreement on the great potential of ubiquitous computing, it is not
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yet clear what the killer applications (i.e., the uses that will result in widespread
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adoption) will be. Many researchers and product developers have created example
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scenarios to demonstrate the potential of the technology. Due to the integrated and
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universal nature of ubiquitous computing, these scenarios tend to include a large
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number of functions rather than any one single application. Thus, some in industry
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have begun to talk in terms of delivering a certain type of user experience rather
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than a particular application or suite of applications. These scenarios tend to involve
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users with several portable devices, moving between different environments (e.g.,
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home, car, office, conference). The devices typically take an active (and often
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annoying) role in reminding the user of various appointments and tasks that are due,
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provide access to any and all information that may be relevant to these tasks, and
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facilitate communication among groups of individuals involved in the tasks.
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Categories of Functionality
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Rather than specify yet another such scenario, it is perhaps more useful to categorize
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the functionalities that such scenarios imply. This categorization can then be
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examined to determine the requirements that are imposed on data management. The
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functionalities can be classified into the following:
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1) Support for mobility the compactness of the devices combined with
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wireless communication means that the devices can be used in mobile
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situations. Thus, existing applications must be able to operate in varied
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and dynamic communication and computation environments, possibly moving from one network or service provider to another. Furthermore,
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new applications that are location-centric will also be developed.
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2) Context awareness if devices become truly ubiquitous, then they will
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be used constantly in a wide range of continually changing situations.
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For the devices to be truly helpful, they must be aware of the
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environment as well as the tasks that the user is performing or will be
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performing in the near future. Context aware applications range from
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intelligent notification systems that inform the user of (hopefully)
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important events or data, to smart spaces , that is, rooms or
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environments that adapt based on who is present and what they are
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doing.
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3) Support for collaboration another key theme of ubiquitous computing
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applications is the support of groups of people. This support consists of
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communications and conferencing as well as the storage, maintenance,
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delivery, and presentation of shared data. Collaborations may be
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performed in real-time, if all of the participants are available, or may be
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done asynchronously otherwise. In addition to supporting on-going
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collaboration, access to and analysis of traces of past activities is also
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required.
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Adaptivity and User Interaction
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These functionalities provide a host of challenges for data management techniques,
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but one requirement is present across all of them, namely, the need for adaptivity.
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Mobile users and devices, changing contexts, and dynamic groups all impose
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requirements for flexibility and responsiveness that are simply not addressed by most
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traditional data management techniques. Thus, adaptivity is a common theme of the
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techniques that we discuss in the remainder of the paper.
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It is also important to note that because ubiquitous computing is intended to
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augment human capabilities in the execution of various tasks, the nature of these
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applications is that the user is typically interacting in real-time with the computers.
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We are able to exploit this fact as part of the solution to adaptivity by, in some cases,
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depending on the users to make dynamic choices or to cope with some degree of
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ambiguity. A concrete example of such a design choice is the way that many
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groupware systems handle concurrent access and update to shared data. Rather than
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impose rules that restrict the types and degrees of interaction that users can have, as is
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done by concurrency control mechanisms in traditional database systems, a
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groupware data manager will typically impose less stringent rules. The relaxation of
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these rules limits the extent to which the system can autonomously handle conflicts.
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Thus, such systems typically handle whatever cases they can, and when they detect a
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conflict that cannot be handled automatically, they simply inform the user(s) that the
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conflict has occurred, and allow them to resolve it based on their knowledge of the
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situation. Thus, having users in the loop can be leveraged to provide more adaptive
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and flexible systems.
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Challenges in Ubiquitous Data Management
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Requirements Due to Mobility
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Other data management requirements are less universal across the three categories but
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yet must be addressed in order to support a comprehensive ubiquitous computing
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environment. For example, the issue of mobility raises a number of issues. First, the
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fact that the terminals (i.e. devices) are constantly moving, and often have limited
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storage capacity means that a ubiquitous computing system must be able to deliver
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