Finding k-Dissimilar Paths with Minimum Collective Length

Shortest path computation is a fundamental problem in road networks. However, in many real-world scenarios, determining solely the shortest path is not enough. In this paper, we study the problem of finding k-Dissimilar Paths with Minimum Collective Length (kDPwML), which aims at computing a set of paths from a source s to a target t such that all paths are pairwise dissimilar by at least \theta and the sum of the path lengths is minimal. We introduce an exact algorithm for the kDPwML problem, which iterates over all possible s-t paths while employing two pruning techniques to reduce the prohibitively expensive computational cost. To achieve scalability, we also define the much smaller set of the simple single-via paths, and we adapt two algorithms for kDPwML queries to iterate over this set. Our experimental analysis on real road networks shows that iterating over all paths is impractical, while iterating over the set of simple single-via paths can lead to scalable solutions with only a small trade-off in the quality of the results.Comment: Extended version of the SIGSPATIAL'18 paper under the same titl

Parallel In-Memory Evaluation of Spatial Joins

The spatial join is a popular operation in spatial database systems and its evaluation is a well-studied problem. As main memories become bigger and faster and commodity hardware supports parallel processing, there is a need to revamp classic join algorithms which have been designed for I/O-bound processing. In view of this, we study the in-memory and parallel evaluation of spatial joins, by re-designing a classic partitioning-based algorithm to consider alternative approaches for space partitioning. Our study shows that, compared to a straightforward implementation of the algorithm, our tuning can improve performance significantly. We also show how to select appropriate partitioning parameters based on data statistics, in order to tune the algorithm for the given join inputs. Our parallel implementation scales gracefully with the number of threads reducing the cost of the join to at most one second even for join inputs with tens of millions of rectangles.Comment: Extended version of the SIGSPATIAL'19 paper under the same titl

Two-layer Space-oriented Partitioning for Non-point Data

Non-point spatial objects (e.g., polygons, linestrings, etc.) are ubiquitous. We study the problem of indexing non-point objects in memory for range queries and spatial intersection joins. We propose a secondary partitioning technique for space-oriented partitioning indices (e.g., grids), which improves their performance significantly, by avoiding the generation and elimination of duplicate results. Our approach is easy to implement and can be used by any space-partitioning index to significantly reduce the cost of range queries and intersection joins. In addition, the secondary partitions can be processed independently, which makes our method appropriate for distributed and parallel indexing. Experiments on real datasets confirm the advantage of our approach against alternative duplicate elimination techniques and data-oriented state-of-the-art spatial indices. We also show that our partitioning technique, paired with optimized partition-to-partition join algorithms, typically reduces the cost of spatial joins by around 50%.Comment: To appear in the IEEE Transactions on Knowledge and Data Engineerin

Pulmonary sarcoidosis associated with psoriasis vulgaris: coincidental occurrence or causal association? Case report

BACKGROUND: Sarcoidosis is rarely associated with a distinct disease. One disease infrequently associated with sarcoidosis is psoriasis. CASE PRESENTATION: This case study describes a 38-year-old male, who presented with chest pain, high-grade fever, arthralgias and a skin rash accompanied by bilateral hilar lymphadenopathy on his chest radiograph. Extensive investigations including fiber-optic bronchoscopy with bronchoalveolar lavage and labial and skin biopsies, demonstrated that two distinct clinical entities co-existed in the same patient: pulmonary sarcoidosis and psoriasis vulgaris. Combination therapy for both diseases was applied and the patient was greatly improved. CONCLUSION: This is the first well-documented case of sarcoidosis and psoriasis in the same patient, reported on the basis of safe and widely-used techniques that were not available until fairly recently. These disorders might share common pathogenic mechanisms that could explain their co-existence in the patient

Use of interrupter technique in assessment of bronchial responsiveness in normal subjects

BACKGROUND: A number of subjects, especially the very young and the elderly, are unable to cooperate and to perform forced expiratory manoeuvres in the evaluation of bronchial hyperresponsiveness (BHR). The objective of our study was to investigate the use of the interrupter technique as a method to measure the response to provocation and to compare it with the conventional PD(20 )FEV(1). METHODS: We studied 170 normal subjects, 100 male and 70 female (mean ± SD age, 38 ± 8.5 and 35 ± 7.5 years, respectively), non-smoking from healthy families. These subjects had no respiratory symptoms, rhinitis or atopic history. A dosimetric cumulative inhalation of methacholine was used and the response was measured by the dose which increases baseline end interruption resistance by 100% (PD(100)Rint, EI) as well as by percent dose response ratio (DRR). RESULTS: BHR at a cut-off level of 0.8 mg methacholine exhibited 31 (18%) of the subjects (specificity 81.2%), 21 male and 10 female, while 3% showed a response in the asthmatic range. The method was reproducible and showed good correlation with PD(20)FEV(1 )(r = 0.76, p < 0.005), with relatively narrow limits of agreement at -1.39 μmol and 1.27 μmol methacholine, respectively, but the interrupter methodology proved more sensitive than FEV(1 )in terms of reactivity (DRR). CONCLUSIONS: Interrupter methodology is clinically useful and may be used to evaluate bronchial responsiveness in normal subjects and in situations when forced expirations cannot be performed

Evaluating queries over route collections

The recent advances in the infrastructure of Geographic Information Systems (GIS), and the proliferation of the GPS technology, have resulted in the abundance of geodata in the form of sequences of spatial locations representing points of interest (POIs), landmarks, waypoints etc. We refer to a set of such sequences as route collection. In many applications, the route collections are frequently updated as new routes are continuously created and included, or existing ones are extended or even deleted. This thesis studies three problems where given a frequently updated route collection the goal is to find a path, i.e., a sequence of spatial locations, that satisfies a number of constraints. According to the first problem a large collection of touristic routes is available and the goal is find a path that connects two landmarks through locations contained in the routes. Second, we focus on the pickup and delivery problems that appear in various logistics and transportation scenarios. A company that offers pickup and delivery services has already scheduled its fleet of vehicles to follow a collection of routes for servicing a number of customer requests. However during the day, new ad-hoc requests arrive at arbitrary times, and the objective is to find sequences of locations from the vehicle routes, i.e., paths, for picking up and delivering the new objects, and minimizing at the same time the company's expenses. Finally, we consider the problem of providing driving directions from one location of a city to another. In this context a collection of vehicle routes is constructed using everyday driving data on the road network of the city. This collection provides a trusted and "familiar" way of driving through the city, in other words it defines a "known" part of the city's network. The drivers consult the collection whenever they want to travel from one location to another, seeking for a path such that they will drive as less time as possible outside the known part of the road network without significantly increasing, at the same time, the total duration of their journey compared to the fastest way, i.e., the shortest path.Οι πρόσφατες εξελίξεις στον τομέα των υπηρεσιών εντοπισμού θέσης (GPS) και η εξάπλωση των εφαρμογών της γεωπληροφορικής έχουν ως αποτέλεσμα τη δημιουργία πληθώρας δεδομένων με τη μορφή ακολουθιών από σημεία ενδιαφέροντος, αξιοθέατα κλπ. Ένα σύνολο τέτοιων ακολουθιών το ονομάζουμε συλλογή διαδρομών. Σε πολλές εφαρμογές οι συλλογές διαδρομών παρουσιάζουν ένα ενδιαφέρον χαρακτηριστικό: ενημερώνονται συχνά είτε με την προσθήκη νέων διαδρομών, είτε με τη διαγραφή ή και την επέκταση υπαρχόντων. Στα πλαίσια της διατριβής αυτής μελετάμε τρία προβλήματα στα οποία μια τέτοια δυναμική συλλογή διαδρομών είναι διαθέσιμη και στόχος είναι η εύρεση ενός μονοπατιού, δηλαδή μιας ακολουθίας σημείων, που να ικανοποιεί δοσμένους περιορισμούς. Το πρώτο πρόβλημα αφορά σε μεγάλες συλλογές τουριστικών διαδρομών και το ζητούμενο είναι η εύρεση ενός μονοπατιού που να συνδέει δύο αξιοθέατα ή σημεία ενδιαφέροντος και να συνδυάζει σημεία αποκλειστικά από τις προτεινόμενες διαδρομές της συλλογής. Το δεύτερο πρόβλημα απαντάται στον τομέα της παροχής υπηρεσιών παραλαβής και παράδοσης πακέτων από εταιρίες ταχυμεταφορών. Μια τέτοια εταιρία κατασκευάζει και διατηρεί καθημερινά μία συλλογή διαδρομών. Τα οχήματα του στόλου της εταιρίας ακολουθούν αυτές τις διαδρομές για να εξυπηρετήσουν τα αιτήματα των πελατών. Ωστόσο κατά τη διάρκεια της ημέρας νέα αιτήματα καταφθάνουν σε τυχαίες χρονικές στιγμές και το ζητούμενο είναι να βρεθούν μονοπάτια που συνδυάζουν τις υπάρχουσες διαδρομές για να παραληφθούν και να παραδοθούν τα νέα πακέτα με τη μικρότερη αύξηση στα λειτουργικά έξοδα της εταιρίας. Τέλος, το τρίτο πρόβλημα σχετίζεται με τη μετακίνηση στο οδικό δίκτυο μιας πόλης. Ας φανταστούμε μία ομάδα οδηγών που καταγράφουν τις καθημερινές μετακινήσεις τους με το αυτοκίνητο στην πόλη. Με αυτό τον τρόπο κατασκευάζεται μία συλλογή διαδρομών που ορίζει ένα ασφαλή και έμπιστο τρόπο μετακίνησης, με άλλα λόγια ένα "γνωστό" κομμάτι του οδικού δικτύου. Γι' αυτό το λόγο κάθε φορά που ένας οδηγός θέλει να μεταβεί από ένα σημείο της πόλης σε ένα άλλο συμβουλεύεται αυτήν τη συλλογή διαδρομών και επιζητά ένα μονοπάτι ώστε να κινηθεί όσο το δυνατό περισσότερο στο "γνωστό" κομμάτι του δικτύου αλλά ταυτόχρονα ο συνολικός χρόνος που θα χρειαστεί να μην είναι μεγαλύτερος κατά ένα ποσοστό από τη διάρκεια του συντομότερου μονοπατιού