Nearly Periodic Facts in Temporal Relational Databases

Despite the huge amount of work devoted to the treatment of time within the relational context, few relevant temporal phenomena still remain to be addressed. One of them is the treatment of \u201cnearly periodic events\u201d, i.e., eventsacts that occur in intervals of time which repeat periodically (e.g., a meeting occurring twice each Monday, possibly not at regular times). Nearly periodic events are quite frequent in everyday life, and thus in many applicative contexts. Their treatment within the relational model is quite challenging, since it involves the integrated treatment of three aspects: (i) the number of repetitions, (ii) their periodicity, and (iii) temporal indeterminacy. Coping with this problem requires an in-depth extension of current temporal relational database techniques. In this paper, we introduce a new data model, and new definitions of relational algebraic operators coping with the above issues. We ascertain the properties of the new model and algebra, with emphasis on the expressiveness of our representation model, on the reducibility property, and on the correctness of the algebraic operators

Statistical Equilibrium in Quantum Gravity: Gibbs states in Group Field Theory

Gibbs states are known to play a crucial role in the statistical description of a system with a large number of degrees of freedom. They are expected to be vital also in a quantum gravitational system with many underlying fundamental discrete degrees of freedom. However, due to the absence of well-defined concepts of time and energy in background independent settings, formulating statistical equilibrium in such cases is an open issue. This is even more so in a quantum gravity context that is not based on any of the usual spacetime structures, but on non-spatiotemporal degrees of freedom. In this paper, after having clarified general notions of statistical equilibrium, on which two different construction procedures for Gibbs states can be based, we focus on the group field theory formalism for quantum gravity, whose technical features prove advantageous to the task. We use the operator formulation of group field theory to define its statistical mechanical framework, based on which we construct three concrete examples of Gibbs states. The first is a Gibbs state with respect to a geometric volume operator, which is shown to support condensation to a low-spin phase. This state is not based on a pre-defined symmetry of the system and its construction is via Jaynes' entropy maximisation principle. The second are Gibbs states encoding structural equilibrium with respect to internal translations on the GFT base manifold, and defined via the KMS condition. The third are Gibbs states encoding relational equilibrium with respect to a clock Hamiltonian, obtained by deparametrization with respect to coupled scalar matter fields.Comment: v2 31 pages; typos corrected; section 2 modified substantially for clarity; minor modifications in the abstract and introduction; arguments and results unchange

Temporal Data Modeling and Reasoning for Information Systems

Temporal knowledge representation and reasoning is a major research field in Artificial Intelligence, in Database Systems, and in Web and Semantic Web research. The ability to model and process time and calendar data is essential for many applications like appointment scheduling, planning, Web services, temporal and active database systems, adaptive Web applications, and mobile computing applications. This article aims at three complementary goals. First, to provide with a general background in temporal data modeling and reasoning approaches. Second, to serve as an orientation guide for further specific reading. Third, to point to new application fields and research perspectives on temporal knowledge representation and reasoning in the Web and Semantic Web

ON PERIODICITY IN TEMPORAL DATABASES

The issue of periodicity is generally understood to be a desirable property of temporal data that should be supported by temporal database models and their query languages. Nevertheless, there has so far not been any systematic examination of how to incorporate this concept into a temporal DBMS. In this paper we describe two concepts of periodicity, which we call strong periodicity and near periodicity, and discuss how they capture formally two of the intuitive meanings of this term. We formally compare the expressive power of these two concepts, relate them to existing temporal query languages, and show how they can be incorporated into temporal relational database query languages, such as the proposed temporal extension to SQL, in a clean and straightforward manner.Information Systems Working Papers Serie

Irregular Indeterminate Repeated Facts in Temporal Relational Databases

Time is pervasive of reality, and many relational database approaches have been developed to cope with it. In practical applications, facts can repeat several times, and only the overall period of time containing all the repetitions may be known (consider, e.g., On January, John attended five meetings of the Bioinformatics project). While some temporal relational databases have faced facts repeated at (known) periodic time, or single facts occurred at temporally indeterminate time, the conjunction of non-periodic repetitions and temporal indeterminacy has not been faced yet. Coping with this problem requires an in-depth extension of current techniques. In this paper, we have introduced a new data model, and new definitions of relational algebraic operators coping with the above issues. We have studied the properties of the new model and algebra (with emphasis on the reducibility property), and how it can be integrated with other models in the literature

Thermal quantum gravity condensates in group field theory cosmology

The condensate cosmology programme of group field theory quantum gravity has produced several interesting results. The key idea is in the suggestion that a macroscopic homogeneous spacetime can be approximated by a dynamical condensate phase of the underlying microscopic system of an arbitrarily large number of candidate quanta of geometry. In this work, we extend the standard treatments in two ways: by using a class of thermal condensates, the coherent thermal states, which encode statistical fluctuations in quantum geometry; and, by introducing a suitable class of smearing functions as non-singular, well-behaved generalisations for relational clock frames in group field theory. In particular, we investigate an effective relational cosmological dynamics for homogeneous and isotropic spacetimes, extracted from a class of free group field theory models, and subsequently investigate aspects of its late and early times evolution. We find the correct classical limit of Friedmann equations at late times, with a bounce and accelerated inflationary expansion at early times. Specifically, we find additional correction terms in the evolution equations corresponding to the statistical contribution of the new thermal condensates in general; and, a higher upper bound on the number of e-folds, even without including any interactions

Application of the Temporal Database Technology in the Development of Latvian Railway Information Systems

The paper presents the research of temporal data usage in the information systems (IS) for railway transport. In the research the IS artifact building phase has been executed. The models and methods oriented at the operation with the temporal objects of the railway transport system have been designed. The work takes into consideration the problems of the temporal objects presentation in the relational databases, as well as the problems of provision of their integrity and the questions of interaction with them. The investigation results have been employed in the development of the interactive passenger train schedule IS for the Latvian Railway

Grammar-Based Random Walkers in Semantic Networks

Semantic networks qualify the meaning of an edge relating any two vertices. Determining which vertices are most "central" in a semantic network is difficult because one relationship type may be deemed subjectively more important than another. For this reason, research into semantic network metrics has focused primarily on context-based rankings (i.e. user prescribed contexts). Moreover, many of the current semantic network metrics rank semantic associations (i.e. directed paths between two vertices) and not the vertices themselves. This article presents a framework for calculating semantically meaningful primary eigenvector-based metrics such as eigenvector centrality and PageRank in semantic networks using a modified version of the random walker model of Markov chain analysis. Random walkers, in the context of this article, are constrained by a grammar, where the grammar is a user defined data structure that determines the meaning of the final vertex ranking. The ideas in this article are presented within the context of the Resource Description Framework (RDF) of the Semantic Web initiative.Comment: First draft of manuscript originally written in November 200

A System Architecture for Temporally Oriented Data Management

Attention to the temporal aspects of data management has intensified in recent years,focusing on data models and related systems that are sensitive to the ubiquitous temporal aspects of data. Both the growing need for easier access to historical data, as well as the imminent availability of mass storage devices, are makingthis apromisingbranchof database research, both practically and theoretically. In this paper we summarize the main results of recent research on temporally sensitive data models, discuss the lessons learned in their development, and assess the prospects and dimculties involved in incorporating a temporal dimension into database management systems (TODBs). Inparticular, three system levels are identified: the external userview of the database; an intermediate view closer to the structure of an existing data model; and an internal or implementation view defined interms of low level data structures. This general architecture coherently incorporates a variety of related research results and development experiences, and serves as the framework for theoretical and implementation research into such system