Efficient Management of Short-Lived Data

Motivated by the increasing prominence of loosely-coupled systems, such as mobile and sensor networks, which are characterised by intermittent connectivity and volatile data, we study the tagging of data with so-called expiration times. More specifically, when data are inserted into a database, they may be tagged with time values indicating when they expire, i.e., when they are regarded as stale or invalid and thus are no longer considered part of the database. In a number of applications, expiration times are known and can be assigned at insertion time. We present data structures and algorithms for online management of data tagged with expiration times. The algorithms are based on fully functional, persistent treaps, which are a combination of binary search trees with respect to a primary attribute and heaps with respect to a secondary attribute. The primary attribute implements primary keys, and the secondary attribute stores expiration times in a minimum heap, thus keeping a priority queue of tuples to expire. A detailed and comprehensive experimental study demonstrates the well-behavedness and scalability of the approach as well as its efficiency with respect to a number of competitors.Comment: switched to TimeCenter latex styl

O2-tree: a shared memory resident index in multicore architectures

Shared memory multicore computer architectures are now commonplace in computing. These can be found in modern desktops and workstation computers and also in High Performance Computing (HPC) systems. Recent advances in memory architecture and in 64-bit addressing, allow such systems to have memory sizes of the order of hundreds of gigabytes and beyond. This now allows for realistic development of main memory resident database systems. This still requires the use of a memory resident index such as T-Tree, and the B+-Tree for fast access to the data items. This thesis proposes a new indexing structure, called the O2-Tree, which is essentially an augmented Red-Black Tree in which the leaf nodes are index data blocks that store multiple pairs of key and value referred to as \key-value" pairs. The value is either the entire record associated with the key or a pointer to the location of the record. The internal nodes contain copies of the keys that split blocks of the leaf nodes in a manner similar to the B+-Tree. O2-Tree structure has the advantage that: it can be easily reconstructed by reading only the lowest value of the key of each leaf node page. The size is su ciently small and thus can be dumped and restored much faster. Analysis and comparative experimental study show that the performance of the O2-Tree is superior to other tree-based index structures with respect to various query operations for large datasets. We also present results which indicate that the O2-Tree outperforms popular key-value stores such as BerkelyDB and TreeDB of Kyoto Cabinet for various workloads. The thesis addresses various concurrent access techniques for the O2-Tree for shared memory multicore architecture and gives analysis of the O2-Tree with respect to query operations, storage utilization, failover and recovery

Scapegoat trees: a comparative performance assessment

Η εργασία αυτή παρουσιάζει και αναλύει μια εναλλακτική μέθοδο για την αποδοτική εξισορρόπηση δυαδικών δέντρων αναζήτησης. Τα δέντρα scapegoat είναι ελαφρώς ισορροπημένα και ανακατασκευάζουν μέρη τους υπό ορισμένες συνθήκες. Η amortized χρονική πολυπλοκότητα για κάθε λειτουργία INSERT ή REMOVE είναι Ο(logn), ενώ η worst-case πραγματική χρονική πολυπλοκότητα μιας FIND είναι Ο(logn). Τα δέντρα scapegoat, σε αντίθεση με τις περισσότερες υλοποιήσεις αυτεξισορροπούμενων BST, δεν απαιτούν επιπλέον δεδομένα (π.χ. χρώματα, βάρη, ύψη) στους κόμβους των δέντρων. Χρησιμοποιούνται διάφορες μετρικές και δοκιμές για τη σύγκριση των δέντρων AVL και scapegoat ως προς τη λειτουργικότητά τους. Τέλος, παρέχουμε δεδομένα ως προς την επίδοση των δέντρων scapegoat σε πιθανές εφαρμογές πραγματικού χρόνου.This Thesis presents and analyzes an alternative tree scheme for the efficient balancing of binary search trees. Scapegoat trees are loosely balanced and restructure parts of themselves on certain conditions. The amortized time complexity for each INSERT or REMOVE operation is Ο(logn), while the worst-case real-time complexity of a FIND one is Ο(logn). Scapegoat trees, unlike most self-balancing BST implementations, do not require extra data (e.g. colors, weights, heights) in the tree nodes. Various metrics and tests are used to compare AVL and scapegoat trees on their functionality. Finally, we provide data as to the performance of scapegoat trees in potential real-time applications

Interactive visualization of information hierarchies and applications on the web

The visualization of information hierarchies is concerned with the presentation of abstract hierarchical information about relationships between various entities. It has many applications in diverse domains such as software engineering, information systems, biology, and chemistry. Information hierarchies are typically modeled by an abstract tree, where vertices are entities and edges represent relationships between entities. The aim of visualizing tree drawings is to automatically produce drawings of trees which clearly reflect the relationships of the information hierarchy. This thesis is primarily concerned with problems related to the automatic generation of area-efficient grid drawings of trees, interactively visualizing information hierarchies, and applying our techniques on Web data. The main achievements of this thesis include: 1. An experimental study on algorithms that produce planar straight-line grid drawings of binary trees, 2. An experimental study that shows the algorithm for producing planar straight-line grid drawings of degree-d trees with n nodes with optimal linear area and with user-defined arbitrary aspect ratio, works well in practice, 3. A rings-based technique for interactively visualizing information hierarchies, in real-time, 4. A survey of Web visualization systems developed to address the lost in cyberspace problem, 5. A separation-based Web visualization system that we present as a viable solution to the lost in cyberspace problem, 6. A rings-based Web visualization system that we propose as a solution to the lost in cyberspace problem

Phylogenetic and Functional Diversity of Saprolegniales and Fungi Isolated from Temperate Lakes in Northeast Germany

Funding: This research was funded by the Iranian Ministry of Science, Research, and Technology and DAAD (German Academic Exchange Service). The APC was funded by the Leibniz Association. Acknowledgments: The publication of this article was funded by the Open Access Fund of the Leibniz Association.Peer reviewedPublisher PD

Search Tree Data Structures and Their Applications

This study concerns the discussion of search tree data structures and their applications. The thesis presents three new top-down updating algorithms for the concurrent data processing environment.Computing and Information Scienc

A Smartphone-based Connected Vehicle Solution for Winter Road Surface Condition Monitoring

The monitoring of winter road surface conditions (RSCs) is essential to transportation agencies and the traveling public, since the former needs to be aware of the location and severity of existing RSCs in order to effectively maintain safe roadways with minimal environmental impact, while the latter uses RSC information to make informed travel decisions. However, current RSC monitoring practice still relies on methods that are time-consuming, labour-intensive and lacking in objectivity, therefore limiting their ability to provide sufficient spatial and temporal coverage across a road network. This research was motivated by the need for accurate, timely and reliable RSC monitoring for winter maintenance personnel and the travelling public. To achieve this objective, the field performance of a smartphone-based RSC monitoring system was evaluated on a section of Highway 6 in Ontario, Canada during the winter of 2014. A comparison between this system and current monitoring methods indicated that the former was capable of providing reliable results particularly at the maintenance route level; however, classification accuracy was found to vary according to RSC type. To improve the results produced by the smartphone-based system, this thesis proposes a connected- vehicle (CV) based RSC monitoring system that utilizes Road Weather Information System (RWIS) data in addition to the smartphone-based system’s data. Three techniques in artificial neural networks (ANNs), random trees (RTs), and random forests (RFs) were tested as the underlying models of the CV system, and the results indicated that all three models successfully increased the classification accuracy of the smartphone-based system. RFs were found to provide the most accurate RSC classifications for the standard (three-class) classification scheme while RTs were found to be most accurate when using a more detailed (five-class) classification scheme. Model transferability was also tested using data captured from a different test site during the winter of 2015; and it was found that although the proposed CV system significantly increased the reliability of RSC classifications, the underlying models were non-transferable and would therefore require local calibration before being used at different sites across a road network