Nikos Giatrakos

HERMES: aggregative LBS via a trajectory DB engine

We present HERMES, a prototype system based on a powerful query language for trajectory databases, which enables the support of aggregative Location-Based Services (LBS). The key observation that motivates HERMES is that the more the knowledge in hand about the trajectory of a mobile user, the better the exploitation of the advances in spatio-temporal query processing for providing intelligent LBS. HERMES is fully incorporated into a state-of-the-art Object-Relational DBMS, and its demonstration illustrates its flexibility and usefulness for delivering custom-defined LBS.

Prediction-based geometric monitoring over distributed data streams

Many modern streaming applications, such as online analysis of financial, network, sensor and other forms of data are inherently distributed in nature. An important query type that is the focal point in such application scenarios regards actuation queries, where proper action is dictated based on a trigger condition placed upon the current value that a monitored function receives. Recent work studies the problem of (non-linear) sophisticated function tracking in a distributed manner. The main concept behind the geometric monitoring approach proposed there, is for each distributed site to perform the function monitoring over an appropriate subset of the input domain. In the current work, we examine whether the distributed monitoring mechanism can become more efficient, in terms of the number of communicated messages, by extending the geometric monitoring framework to utilize prediction models. We initially describe a number of local estimators (predictors) that are useful for the applications that we consider and which have already been shown particularly useful in past work. We then demonstrate the feasibility of incorporating predictors in the geometric monitoring framework and show that prediction-based geometric monitoring in fact generalizes the original geometric monitoring framework. We propose a large variety of different prediction-based monitoring models for the distributed threshold monitoring of complex functions. Our extensive experimentation with a variety of real data sets, functions and parameter settings indicates that our approaches can provide significant communication savings ranging between two times and up to three orders of magnitude, compared to the transmission cost of the original monitoring framework.

SeTraStream: semantic-aware trajectory construction over streaming movement data

Location data generated from GPS equipped moving objects are typically collected as streams of spatiotemporal 〈x, y, t〉 points that when put together form corresponding trajectories. Most existing studies focus on building ad-hoc querying, analysis, as well as data mining techniques on formed trajectories. As a prior step, trajectory construction is evidently necessary for mobility data processing and understanding, including tasks like trajectory data cleaning, compression, and segmentation so as to identify semantic trajectory episodes like stops (e.g. while sitting and standing) and moves (while jogging, walking, driving etc). However, semantic trajectory construction methods in the current literature are typically based on offline procedures, which is not sufficient for real life trajectory applications that rely on timely delivery of computed trajectories to serve real-time query answers. Filling this gap, our paper proposes a platform, namely SeTraStream, for online semantic trajectory construction. Our framework is capable of providing real-time trajectory data cleaning, compression, segmentation over streaming movement data.

T-Warehouse: Visual OLAP analysis on trajectory data

Technological advances in sensing technologies and wireless telecommunication devices enable novel research fields related to the management of trajectory data. As it usually happens in the data management world, the challenge after storing the data is the implementation of appropriate analytics for extracting useful knowledge. However, traditional data warehousing systems and techniques were not designed for analyzing trajectory data. Thus, in this work, we demonstrate a framework that transforms the traditional data cube model into a trajectory warehouse. As a proof-of-concept, we implemented T-WAREHOUSE, a system that incorporates all the required steps for Visual Trajectory Data Warehousing, from trajectory reconstruction and ETL processing to Visual OLAP analysis on mobility data.

TACO: tunable approximate computation of outliers in wireless sensor networks

Wireless sensor networks are becoming increasingly popular for a variety of applications. Users are frequently faced with the surprising discovery that readings produced by the sensing elements of their motes are often contaminated with outliers. Outlier readings can severely affect applications that rely on timely and reliable sensory data in order to provide the desired functionality. As a consequence, there is a recent trend to explore how techniques that identify outlier values can be applied to sensory data cleaning. Unfortunately, most of these approaches incur an overwhelming communication overhead, which limits their practicality. In this paper we introduce an in-network outlier detection framework, based on locality sensitive hashing, extended with a novel boosting process as well as efficient load balancing and comparison pruning mechanisms. Our method trades off bandwidth for accuracy in a straightforward manner and supports many intuitive similarity metrics.

HERMES: A Trajectory DB Engine for Mobility-Centric Applications

This paper presents HERMES, a prototype DB engine that defines a powerful query language for trajectory databases, which enables the support of mobility-centric applications, such as Location-Based Services LBS. HERMES extends the data definition and manipulation language of Object-Relational DBMS ORDBMS with spatio-temporal semantics and functionality based on advanced spatio-temporal indexing and query processing techniques. Its implementation over two ORDBMS and its utilization in various domains proves the expressive power and applicability of HERMES in different application domains where knowledge regarding mobility data is essential. As a proof-of-concept, in this paper HERMES is applied to a case study related with vehicle traffic analysis, demonstrating its flexibility and usefulness for delivering custom-defined LBS.

In-network approximate computation of outliers with quality guarantees

Wireless sensor networks are becoming increasingly popular for a variety of applications. Users are frequently faced with the surprising discovery that readings produced by the sensing elements of their motes are often contaminated with outliers. Outlier readings can severely affect applications that rely on timely and reliable sensory data in order to provide the desired functionality. As a consequence, there is a recent trend to explore how techniques that identify outlier values based on their similarity to other readings in the network can be applied to sensory data cleaning. Unfortunately, most of these approaches incur an overwhelming communication overhead, which limits their practicality. In this paper we introduce an in-network outlier detection framework, based on locality sensitive hashing, extended with a novel boosting process as well as efficient load balancing and comparison pruning mechanisms. Our method trades off bandwidth for accuracy in a straightforward manner and supports many intuitive similarity metrics. Our experiments demonstrate that our framework can reliably identify outlier readings using a fraction of the bandwidth and energy that would otherwise be required.

PAO: power-efficient attribution of outliers in wireless sensor networks

Sensor nodes constitute inexpensive, disposable devices that are often scattered in harsh environments of interest so as to collect and communicate desired measurements of monitored quantities. Due to the commodity hardware used in the construction of sensor nodes, the readings of sensors are frequently tainted with outliers. Given the presence of outliers, decision making in sensor networks becomes much harder. In this work, we introduce PAO, a framework that can reliably and efficiently detect outliers in wireless sensor networks. PAO significantly reduces the bandwidth consumption during the outlier detection procedure, while being able to operate over multiple window types. Moreover, our framework possesses the ability to operate in either an exact mode, or an approximate one that further reduces the communication cost, thus covering a wide variety of application requirements.

Issues in complex event processing

Research issues in complex event processing (CEP) emphasizing on query optimization.Cover deterministic probabilistic models, centralized distributed settings.Issues for CEP optimization over Big Data enabling cloud computing platforms.Predictive Analytics and CEP in cloud platforms even with dispersed resource pools. Many Big Data technologies were built to enable the processing of human generated data, setting aside the enormous amount of data generated from Machine-to-Machine (M2M) interactions and Internet-of-Things (IoT) platforms. Such interactions create real-time data streams that are much more structured, often in the form of series of event occurrences. In this paper, we provide an overview on the main research issues confronted by existing Complex Event Processing (CEP) techniques, with an emphasis on query optimization aspects. Our study expands on both deterministic and probabilistic event models and spans from centralized to distributed network settings. In that, we cover a wide range of approaches in the CEP domain and review the current status of techniques that tackle efficient query processing. These techniques serve as a starting point for developing Big Data oriented CEP applications. Therefore, we further study the issues that arise upon trying to apply those techniques over Big Data enabling technologies, as is the case with cloud platforms. Furthermore, we expand on the synergies among Predictive Analytics and CEP with an emphasis on scalability and elasticity considerations in cloud platforms with potentially dispersed resource pools.

FERARI: A Prototype for Complex Event Processing over Streaming Multi-cloud Platforms

In this demo, we present FERARI, a prototype that enables real-time Complex Event Processing (CEP) for large volume event data streams over distributed topologies. Our prototype constitutes, to our knowledge, the first complete, multi-cloud based end-to-end CEP solution incorporating: a) a user-friendly, web-based query authoring tool, (b) a powerful CEP engine implemented on top of a streaming cloud platform, (c) a CEP optimizer that chooses the best query execution plan with respect to low latency and/or reduced inter-cloud communication burden, and (d) a query analytics dashboard encompassing graph and map visualization tools to provide a holistic picture with respect to the detected complex events to final stakeholders. As a proof-of-concept, we apply FERARI to enable mobile fraud detection over real, properly anonymized, telecommunication data from T-Hrvatski Telekom network in Croatia.