Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Random graphs

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Convex Analysisの二,三の進展について

Data integration is the problem of combining data residing at different sources, and providing the user with a unified view of these data. The problem of designing data integration systems is important in current real world applications, and is characterized by a number of issues that are interesting from a theoretical point of view. This document presents on overview of the material to be presented in a tutorial on data integration. The tutorial is focused on some of the theoretical issues that are relevant for data integration. Special attention will be devoted to the following aspects: modeling a data integration application, processing queries in data integration, dealing with inconsistent data sources, and reasoning on queries.

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Data integration: a theoretical perspective

Optimization, approximation, and complexity classes

The consistent query answering framework has received considerable attention since it was first introduced as an alternative to coping with inconsistent databases. The framework was defined based on two notions: repairs and consistent query answers. Informally, a repair is a consistent database that minimally differs from the inconsistent database. The consistent answers to a query are those tuples that appear in the intersection of the answer sets of the query when evaluated over all possible repairs. Here we study the complexity of the problem of consistent query answering for the class of acyclic conjunctive queries without self-joins, under primary key constraints. The problem is known to be coNP-complete in general for this class. Our goal is to determine the boundary between tractability and intractability, by establishing a dichotomy to the effect that, every conjunctive query in this class is either in PTIME or coNP-complete. In the PTIME direction, previous work has identified the queries for which consistent answers can be computed via first-order rewriting. In fact, for the class of acyclic conjunctive queries without self-joins, under primary key constraints, the boundary between first-order rewritable and not first-order rewritable queries has already been determined. Hence, our focus is on queries for which there is no first-order rewriting. We present a technique for computing in polynomial time the consistent query answers to several not first-order rewritable queries. We hope this technique may lay the foundations for a more general algorithm that handles all PTIME not first-order rewritable queries. In the hardness direction, we identify several representative queries of the class, for which we show that the problem is coNP-hard.This work is done under the supervision of Prof. Phokion G. Kolaitis and Prof. Wang-Chiew Tan.

On the tractability and intractability of consistent conjunctive query answering

We develop a unifying approach to declarative entity linking by introducing the notion of an entity linking framework and an accompanying notion of the certain links in such a framework. In an entity linking framework, logic-based constraints are used to express properties of the desired link relations in terms of source relations and, possibly, in terms of other link relations. The definition of the certain links in such a framework makes use of weighted repairs and consistent answers in inconsistent databases. We demonstrate the modeling capabilities of this approach by showing that numerous concrete entity linking scenarios can be cast as such entity linking frameworks for suitable choices of constraints and weights. By using the certain links as a measure of expressive power, we investigate the relative expressive power of several entity linking frameworks and obtain sharp comparisons. In particular, we show that we gain expressive power if we allow constraints that capture non-recursive collective entity resolution, where link relations may depend on other link relations (and not just on source relations). Moreover, we show that an increase in expressive power also takes place when we allow constraints that incorporate preferences as an additional mechanism for expressing "goodness" of links.

Expressive Power of Entity-Linking Frameworks

Every logical formalism gives rise to two fundamental algorithmic problems: model checking and inference. In propositional logic, the model checking problem is polynomial-time solvable, while the inference problem is coNP-complete. In propositional circumscription, however, these problems have higher computational complexity, namely the model checking problem is coNP-complete, while the inference problem is II2P-complete. In this paper, we survey recent results on the computational complexity of restricted cases of these problems in the context of Schaefer's framework of generalized satisfiability problems. These results establish dichotomies in the complexity of the model checking problem and the inference problem for propositional circumscription. Specifically, in each restricted case the model checking problem for propositional circumscription either is coNP-complete or is polynomial-time solvable. Furthermore, in each restricted case the inference problem for propositional circumscription either is II2p-complete or is in coNP. These dichotomy theorems yield a complete classification of the "hard" and the "easier" cases of the model checking problem and the inference problem for propositional circumscription. Moreover, they provide efficiently checkable criteria that tell apart the "hard" cases from the "easier" ones.

On the Complexity of Model Checking and Inference in Minimal Models

We develop a novel framework that aims to create bridges between the computational social choice and the database management communities. This framework enriches the tasks currently supported in computational social choice with relational database context, thus making it possible to formulate sophisticated queries about voting rules, candidates, voters, issues, and positions. At the conceptual level, we give rigorous semantics to queries in this framework by introducing the notions of necessary answers and possible answers to queries. At the technical level, we embark on an investigation of the computational complexity of the necessary answers. We establish a number of results about the complexity of the necessary answers of conjunctive queries involving positional scoring rules that contrast sharply with earlier results about the complexity of the necessary winners.

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Computational social choice meets databases

A positive first-order formula is bounded if the sequence of its stages converges to the least fixed point of the formula within a fixed finite number of steps independent of the input structure. The boundedness problem for a fragment C of first-order logic is the following decision problem: given a positive formula in L, is it bounded? In this paper, we investigate the boundedness problem for two-variable first-order logic FO/sup 2/. As a general rule, FO/sup 2/ is a well-behaved fragment of first-order logic, since it possesses the finite-model property and has a decidable satisfiability problem. Nonetheless, our main result asserts that the boundedness problem for FO/sup 2/ is undecidable, even when restricted to negation-free and equality-free formulas /spl phi/(X, x) in which x is the only free variable and X is a monadic relation symbol that occurs within the scopes of universal quantifiers only. This undecidability result contrasts sharply with earlier results asserting the decidability of boundedness for monadic Datalog programs, which amounts to the decidability of boundedness for negation-free and equality-free existential first-order formulas /spl psi/(X, x) in which x is the only free variable and X is a monadic relation symbol. We demonstrate that our main result has certain applications to circumscription, the most well-developed formalism of nonmonotonic reasoning. Specifically, using the undecidability of boundedness for FO/sup 2/, we show that it is an undecidable problem to tell whether the circumscription of a given FO/sup 2/-formula is equivalent to a first-order formula. In contrast, the circumscription of every FO/sup 1/-formula is equivalent to a first-order formula.

Phokion G. Kolaitis

Papers

On the tractability and intractability of consistent conjunctive query answering

Expressive Power of Entity-Linking Frameworks

On the Complexity of Model Checking and Inference in Minimal Models

Computational social choice meets databases

On the boundedness problem for two-variable first-order logic