Polynomial conjunctive query rewriting under unary inclusion dependencies

Ontology-based data access (OBDA) is widely accepted as an important ingredient of the new generation of information systems. In the OBDA paradigm, potentially incomplete relational data is enriched by means of ontologies, representing intensional knowledge of the application domain. We consider the problem of conjunctive query answering in OBDA. Certain ontology languages have been identified as FO-rewritable (e.g., DL-Lite and sticky-join sets of TGDs), which means that the ontology can be incorporated into the user's query, thus reducing OBDA to standard relational query evaluation. However, all known query rewriting techniques produce queries that are exponentially large in the size of the user's query, which can be a serious issue for standard relational database engines. In this paper, we present a polynomial query rewriting for conjunctive queries under unary inclusion dependencies. On the other hand, we show that binary inclusion dependencies do not admit polynomial query rewriting algorithms

Past Lifetime and Inactivity Time: from Entropy to Coherent Systems

Information Theory was originally proposed by Claude Shannon in 1948 in the landmark paper entitled "A Mathematical Theory of Communication". In this paper the concept of entropy was adopted for the first time in a field other than thermodynamics and statistical mechanics. Since then, the interest in entropy has grown more and more and the current literature now focuses mainly on the analysis of residual lifetime. However, in recent years the interest has 'changed direction'. New notions of entropy have been introduced and are used to describe the past lifetime and the inactivity time of a given system or of a component that is found not to be working at the current time. Moreover inferences about the history of a system may be of interest in real life situations. So, the past lifetime and the inactivity time can also be analysed in the context of the theory of coherent systems

The ALICE Silicon Pixel Detector Control and Calibration Systems

The work presented in this thesis was carried out in the Silicon Pixel Detector (SPD) group of the ALICE experiment at the Large Hadron Collider (LHC). The SPD is the innermost part (two cylindrical layers of silicon pixel detec- tors) of the ALICE Inner Tracking System (ITS). During the last three years I have been strongly involved in the SPD hardware and software development, construction and commissioning. This thesis is focused on the design, development and commissioning of the SPD Control and Calibration Systems. I started this project from scratch. After a prototyping phase now a stable version of the control and calibration systems is operative. These systems allowed the detector sectors and half-barrels test, integration and commissioning as well as the SPD commissioning in the experiment. The integration of the systems with the ALICE Experiment Control System (ECS), DAQ and Trigger system has been accomplished and the SPD participated in the experimental December 2007 commissioning run. The complexity of the detectors, the high number of subcomponents and the harsh working environment make necessary the development of a control system parallel to the data acquisition. This online slow control, called Detector Control System (DCS), has the task of controlling and monitoring all hardware and software components of the detector and of the necessary infrastructures. The latter include the power distribution system, cool ing, interlock system, etc. In this scenario, the DCS assumes a key role. Its functionalities have extended well over the simple control and monitoring of the experiment. DCS, nowadays, are highly advanced and automated online data acquisition systems, with less stringent requirements compared to the DAQ. Moreover the SPD DCS has the unique feature of not only controlling but also operating the SPD front-end electronics. These requirements impose a high level of synchronization between the system components and a fast system response. The DCS, in this case, is a fundamental component for the detector calibration. The SPD DCS should be operated in the ALICE DCS framework hence a series of integration constraint should be applied to the system. Furthermore, in complex experiments such as ALICE, the detector operation is tightly bound to the connection and integration of the various systems such as DAQ, DCS, trigger system, Experiment Control System (ECS) and Offline framework. The operation of the SPD front-end electronics and services should be done at various levels of integration. At the first and bottom level it is required that each system runs safely and independently. At the second level the subsystem controls should be merged to form a unique entity. At this stage the components operation should be synchronized to reach the full detector operation. The third level requires the integration of the SPD control in the genera l ALICE DCS/ECS. These requirements have been fulfilled by designing the DCS with two main software layers. On the bottom a Supervisory Control And Data Acquisition (SCADA) layer controls and monitors the equipments. It is based on a commercial application, PVSS, and it also responsible of provide an user interface to the subsystem components. On top a Finite State Machine (FSM) Layer performs the logical connection between the SPD subsystems and it connects the SPD DCS with the ALICE DCS and ECS. PVSS is designed for slow control applications and it is not suitable for the direct control of the fast SPD front-end electronics. I designed a Front-End Device Server (FED Server) to interface the SCADA layer with the front-end electronics. The server receives macro-instructions from the SCADA and it operates autonomously the complex front-end electronics. The complexity of the detector calibration requires a high automation level and the integration of the calibration system with the ALICE calibration framework. In order to satisfy these requirements and provide the user with a simple and versatile interface, I decided to foresee two calibration scenarios. A calibration scenario, named DAQ ACTIVE, allows the fast detector calibration but it needs the control of the full detector and subsystems. A second calibration scenario, named DCS ONLY, slower than the DAQ ACTIVE scenario, allows the calibration of a detector partition without interference with the normal detector operation. The control and calibration systems have been used to characterize and test the SPD components before and after the integration in the detector, both in laboratory (DSF) and in the ALICE environment. Some calibration and control systems application examples as well as a brief overview of the detector performance evaluated during the commissioning phases are reported

Advanced 3D photogrammetric surface reconstruction of extensive objects by UAV camera image acquisition

This paper proposes a replicable methodology to enhance the accuracy of the photogrammetric reconstruction of large-scale objects based on the optimization of the procedures for Unmanned Aerial Vehicle (UAV) camera image acquisition. The relationships between the acquisition grid shapes, the acquisition grid geometric parameters (pitches, image rates, camera framing, flight heights), and the 3D photogrammetric surface reconstruction accuracy were studied. Ground Sampling Distance (GSD), the necessary number of photos to assure the desired overlapping, and the surface reconstruction accuracy were related to grid shapes, image rate, and camera framing at different flight heights. The established relationships allow to choose the best combination of grid shapes and acquisition grid geometric parameters to obtain the desired accuracy for the required GSD. This outcome was assessed by means of a case study related to the ancient arched brick Bridge of the Saracens in Adrano (Sicily, Italy). The reconstruction of the three-dimensional surfaces of this structure, obtained by the efficient Structure-From-Motion (SfM) algorithms of the commercial software Pix4Mapper, supported the study by validating it with experimental data. A comparison between the surface reconstruction with different acquisition grids at different flight heights and the measurements obtained with a 3D terrestrial laser and total station-theodolites allowed to evaluate the accuracy in terms of Euclidean distances