Vassilis Stoumpos

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— Recent work has demonstrated that readings provided by commodity sensor nodes are often of poor quality. In order to provide a valuable sensory infrastructure for monitoring applications, we first need to devise techniques that can withstand " dirty " and unreliable data during query processing. In this paper we present a novel aggregation framework that(More)
Sensor networks are increasingly applied for monitoring diverse environments and applications. Due to their unsupervised nature of operation and inexpensive hardware used, sensor nodes may furnish readings of rather poor quality. We thus need to devise techniques that can withstand "dirty" data during query processing. In this paper we introduce a robust(More)
Complex on-demand data retrieval and processing is a characteristic of several applications and combines the notions of querying & search, information filtering & retrieval, data transformation & analysis, and other data manipulations. Such rich tasks are typically represented by data processing graphs, having arbitrary data operators as nodes and their(More)
— In this paper we discuss a robust aggregation framework that can detect spurious measurements and refrain from incorporating them in the computed aggregate values. Our framework can consider different definitions of an outlier node, based on a specified minimum support. Our experimental evaluation demonstrates the benefits of our approach.
In this paper we present algorithms for building and maintaining efficient collection trees that provide the conduit to disseminate data required for processing monitoring queries in a wireless sensor network. While prior techniques base their operation on the assumption that the sensor nodes that collect data relevant to a specified query need to include(More)
Contemporary long-term storage devices feature powerful embedded processors and sizeable memory buffers. Active Storage Devices (ASD) is the hard disk technology that makes use of these significant resources to not only manage the disk operation but also to execute custom application code on large amounts of data. While prior research has shown that ASDs(More)
Keywords: Scheduling of block-devices Anticipatory scheduling Kernel structures a b s t r a c t Anticipatory scheduling (AS) of I/O requests has become a viable choice for block-device schedulers in open-source OS-kernels as prior work has established its superiority over traditional disk-scheduling policies. An AS-scheduler selectively stalls the(More)
In this paper we present algorithms for building and maintaining efficient collection trees that provide the conduit to disseminate data required for processing monitoring queries in a wireless sensor network. While prior techniques base their operation on the assumption that the sensor nodes that collect data relevant to a specified query need to include(More)
—The predicates in a non-equi-join can be anything but equality relations. Non-equi-join predicates can be as simple as an inequality expression between two join relation fields, or as complex as a user-defined function that carries out arbitrary complex comparisons. The nature of non-equi-join calls for predicate evaluation over all possible combinations(More)
In this paper we present algorithms for building and maintaining efficient aggregation trees that provide the conduit to disseminate data required for processing monitoring queries in a wireless sensor network. While prior techniques base their operation on the assumption that the sensor nodes that collect data relevant to a specified query need to include(More)
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