Presence Of Functional Dependencies Research Articles

Querying Incomplete Data: Complexity and Tractability via Datalog and First-Order Rewritings

Abstract To answer database queries over incomplete data, the gold standard is finding certain answers: those that are true regardless of how incomplete data is interpreted. Such answers can be found efficiently for conjunctive queries and their unions, even in the presence of constraints. With negation added, the problem becomes intractable however. We concentrate on the complexity of certain answers under constraints and on effficiently answering queries outside the usual classes of (unions) of conjunctive queries by means of rewriting as Datalog and first-order queries. We first notice that there are three different ways in which query answering can be cast as a decision problem. We complete the existing picture and provide precise complexity bounds on all versions of the decision problem, for certain and best answers. We then study a well-behaved class of queries that extends unions of conjunctive queries with a mild form of negation. We show that for them, certain answers can be expressed in Datalog with negation, even in the presence of functional dependencies, thus making them tractable in data complexity. We show that in general, Datalog cannot be replaced by first-order logic, but without constraints such a rewriting can be done in first order.

Standards of specialized diabetes care. Edited by Dedov I.I., Shestakova M.V., Mayorov A.Yu. 9th edition

Dear Colleagues!
 We are glad to present the 9th Edition (revised) of Standards of Diabetes Care. These evidence-based guidelines were designed to standardize and facilitate diabetes care in all regions of the Russian Federation.
 The Standards are updated on the regular basis to incorporate new data and relevant recommendations from national and international clinical societies, including World Health Organization Guidelines (WHO, 2011, 2013), International Diabetes Federation (IDF, 2011, 2012, 2013), American Diabetes Association (ADA, 2018, 2019), American Association of Clinical Endocrinologists (AACE, 2019), International Society for Pediatric and Adolescent Diabetes (ISPAD, 2014, 2018) and Russian Association of Endocrinologists (RAE, 2011, 2012, 2015). Current edition of the Standards also integrates results of completed randomized clinical trials (ADVANCE, ACCORD, VADT, UKPDS, SAVOR, TECOS, LEADER, EXAMINE, ELIXA, SUSTAIN, DEVOTE, EMPA-REG OUTCOME, CANVAS, DECLARE, CARMELINA, REWIND, etc.), as well as findings from the national studies of diabetes mellitus (DM), conducted in close partnership with a number of Russian hospitals.
 Latest data indicates that prevalence of DM in the world increased during the last decade more than two-fold, reaching some 463 million patients by the end of 2019. According to the current estimation by the International Diabetes Federation, 578 million patients will be suffering from diabetes mellitus by by 2030 and 700 million by 2045.
 Like many other countries, Russian Federation experiences a sharp rise in the prevalence of DM. According to Russian Federal Diabetes Register, there are at least 4 584 575 patients with DM in this country by the end of 2018 (3,1% of population) with 92% (4 238 503) Type 2 DM, 6% (256 202) Type 1 DM and 2% (89 870) other types of DM, including 8 006 women with gestational DM. However, these results underestimates real quantity of patients, because they consider only registered cases. Results of Russian epidemiological study (NATION) con- firmed that only 54% of Type 2 DM are diagnosed. So real number of patients with DM in Russia is 9 million patients (about 6% of population). This is a great long-term problem, because a lot of patients are not diagnosed, so they dont receive any treatment ant have high risk of vascular complications.
 Severe consequences of the global pandemics of DM include its vascular complications: nephropathy, retinopathy, coronary, cerebral, coronary and peripheral vascular disease. These conditions are responsible for the majority of cases of diabetes-related disability and death.
 In сurrent edition of the Standards:
 
 New goals of glycemic control for the elderly, based on the presence of functional dependence, as well as for pregnant women, children and adolescents, are given.
 Added a snippet that describes the continuous glucose monitoring.
 Only low-density lipoprotein cholesterol level is used as a target for lipid metabolism.
 Proposes more stringent target levels of blood pressure.
 It also features updated guidelines on stratification of treatment in newly diagnosed Type 2 diabetes: the excess of the initial level of HbA1c over the target level was used as a criterion.
 In the recommendations for the personalization of the choice of antidiabetic agents, it is taken into account that in certain clinical situations (the presence of atherosclerotic cardiovascular diseases and their risk factors, chronic heart failure, chronic kidney disease, obesity, the risk of hypoglycemia) certain classes of hypoglycemic agents (or individual drugs) have proven advantages.
 Recommendations for psychosocial support are added.
 The position of metabolic surgery as a method of treatment of DM with morbid obesity is updated.
 Recommendations for diagnostic and treatment of hypogonadism syndrome in men with DM are added.
 For the first time, evidence levels of confidence and credibility levels of recommendations for diagnostic, therapeutic, rehabilitative and preventive interventions based on a systematic review of the literature are given in accordance with the recommendations of the Center for Healthcare Quality Assessment and Control of the Ministry of Health of the Russian Federation.
 
 This text represents a consensus by the absolute majority of national experts, achieved through a number of fruitful discus- sions held at national meetings and forums.
 These guidelines are intended for endocrinologists, primary care physicians and other medical professionals involved in the treatment of DM.
 On behalf of the Working Group

Standards of specialized diabetes care. Edited by Dedov I.I., Shestakova M.V., Mayorov A.Yu. 9th edition

Dear Colleagues!
 We are glad to present the 9th Edition (revised) of Standards of Diabetes Care. These evidence-based guidelines were designed to standardize and facilitate diabetes care in all regions of the Russian Federation.
 The Standards are updated on the regular basis to incorporate new data and relevant recommendations from national and international clinical societies, including World Health Organization Guidelines (WHO, 2011, 2013), International Diabetes Federation (IDF, 2011, 2012, 2013), American Diabetes Association (ADA, 2018, 2019), American Association of Clinical Endocrinologists (AACE, 2019), International Society for Pediatric and Adolescent Diabetes (ISPAD, 2014, 2018) and Russian Association of Endocrinologists (RAE, 2011, 2012, 2015). Current edition of the Standards also integrates results of completed randomized clinical trials (ADVANCE, ACCORD, VADT, UKPDS, SAVOR, TECOS, LEADER, EXAMINE, ELIXA, SUSTAIN, DEVOTE, EMPA-REG OUTCOME, CANVAS, DECLARE, CARMELINA, REWIND, etc.), as well as findings from the national studies of diabetes mellitus (DM), conducted in close partnership with a number of Russian hospitals.
 Latest data indicates that prevalence of DM in the world increased during the last decade more than two-fold, reaching some 463 million patients by the end of 2019. According to the current estimation by the International Diabetes Federation, 578 million patients will be suffering from diabetes mellitus by by 2030 and 700 million by 2045.
 Like many other countries, Russian Federation experiences a sharp rise in the prevalence of DM. According to Russian Federal Diabetes Register, there are at least 4 584 575 patients with DM in this country by the end of 2018 (3,1% of population) with 92% (4 238 503) Type 2 DM, 6% (256 202) Type 1 DM and 2% (89 870) other types of DM, including 8 006 women with gestational DM. However, these results underestimates real quantity of patients, because they consider only registered cases. Results of Russian epidemiological study (NATION) con- firmed that only 54% of Type 2 DM are diagnosed. So real number of patients with DM in Russia is 9 million patients (about 6% of population). This is a great long-term problem, because a lot of patients are not diagnosed, so they dont receive any treatment ant have high risk of vascular complications.
 Severe consequences of the global pandemics of DM include its vascular complications: nephropathy, retinopathy, coronary, cerebral, coronary and peripheral vascular disease. These conditions are responsible for the majority of cases of diabetes-related disability and death.
 In сurrent edition of the Standards:
 
 New goals of glycemic control for the elderly, based on the presence of functional dependence, as well as for pregnant women, children and adolescents, are given.
 Added a snippet that describes the continuous glucose monitoring.
 Only low-density lipoprotein cholesterol level is used as a target for lipid metabolism.
 Proposes more stringent target levels of blood pressure.
 It also features updated guidelines on stratification of treatment in newly diagnosed Type 2 diabetes: the excess of the initial level of HbA1c over the target level was used as a criterion.
 In the recommendations for the personalization of the choice of antidiabetic agents, it is taken into account that in certain clinical situations (the presence of atherosclerotic cardiovascular diseases and their risk factors, chronic heart failure, chronic kidney disease, obesity, the risk of hypoglycemia) certain classes of hypoglycemic agents (or individual drugs) have proven advantages.
 Recommendations for psychosocial support are added.
 The position of metabolic surgery as a method of treatment of DM with morbid obesity is updated.
 Recommendations for diagnostic and treatment of hypogonadism syndrome in men with DM are added.
 For the first time, evidence levels of confidence and credibility levels of recommendations for diagnostic, therapeutic, rehabilitative and preventive interventions based on a systematic review of the literature are given in accordance with the recommendations of the Center for Healthcare Quality Assessment and Control of the Ministry of Health of the Russian Federation.
 
 This text represents a consensus by the absolute majority of national experts, achieved through a number of fruitful discus- sions held at national meetings and forums.
 These guidelines are intended for endocrinologists, primary care physicians and other medical professionals involved in the treatment of DM.
 On behalf of the Working Group

Enumeration Complexity of Conjunctive Queries with Functional Dependencies

We study the complexity of enumerating the answers of Conjunctive Queries (CQs) in the presence of Functional Dependencies (FDs). Our focus is on the ability to list output tuples with a constant delay in between, following a linear-time preprocessing. A known dichotomy classifies the acyclic self-join-free CQs into those that admit such enumeration, and those that do not. However, this classification no longer holds in the common case where the database exhibits dependencies among attributes. That is, some queries that are classified as hard are in fact tractable if dependencies are accounted for. We establish a generalization of the dichotomy to accommodate FDs; hence, our classification determines which combination of a CQ and a set of FDs admits constant-delay enumeration with a linear-time preprocessing. In addition, we generalize a hardness result for cyclic CQs to accommodate unary FDs, and further conclusions of our development include a dichotomy for enumeration with linear delay. Finally, we show that all our results apply also for CQs with disequalities and in the presence of cardinality dependencies that generalize FDs.

Multi-tuple deletion propagation

This paper studies the computational complexity of the classic problem of deletion propagation in a relational database, where tuples are deleted from the base relations in order to realize a desired deletion of tuples from the view. Such an operation may result in a (sometimes unavoidable) side effect: deletion of additional tuples from the view, besides the intentionally deleted ones. The goal is to minimize the side effect. The complexity of this problem has been well studied in the case where only a single tuple is deleted from the view. However, only little is known within the more realistic scenario of multi-tuple deletion, which is the topic of this paper. The class of conjunctive queries (CQs) is among the most well studied in the literature, and we focus here on views defined by CQs that are self-join free (sjf-CQs). Our main result is a trichotomy in complexity, classifying all sjf-CQs into three categories: those for which the problem is in polynomial time, those for which the problem is NP-hard but polynomial-time approximable (by a constant-factor), and those for which even an approximation (by any factor) is NP-hard to obtain. A corollary of this trichotomy is a dichotomy in the complexity of deciding whether a side-effect-free solution exists, in the multi-tuple case. We further extend the full classification to accommodate the presence of a constant upper bound on the number of view tuples to delete, and the presence of functional dependencies. Finally, we establish (positive and negative) complexity results on approximability for the dual problem of maximizing the number of view tuples surviving (rather than minimizing the side effect incurred in) the deletion propagation.

Ambiguity and context-dependent overloading

Abstract This paper discusses ambiguity in the context of languages that support context-dependent overloading, such as Haskell. A type system for a Haskell-like programming language that supports context-dependent overloading and follow the Hindley-Milner approach of providing context-free type instantiation, allows distinct derivations of the same type for ambiguous expressions. Such expressions are usually rejected by the type inference algorithm, which is thus not complete with respect to the type system. Also, Haskell’s open world approach considers a definition of ambiguity that does not conform to the existence of two or more distinct type system derivations for the same type. The article presents an alternative approach, where the standard definition of ambiguity is followed. A type system is presented that allows only context-dependent type instantiation, enabling only one type to be derivable for each expression in a given typing context: the type of an expression can be instantiated only if required by the program context where the expression occurs. We define a notion of greatest instance type for each occurrence of an expression, which is used in the definition of a standard dictionary-passing semantics for core Haskell based on type system derivations, for which coherence is trivial. Type soundness is obtained as a result of disallowing all ambiguous expressions and all expressions involving unsatisfiability in the use of overloaded names. Following the standard definition of ambiguity, satisfiability is tested—i.e., “the world is closed” —if only if overloading is (or should have been) resolved, that is, if and only if there exist unreachable variables in the constraints on types of expressions. Nowadays, satisfiability is tested in Haskell, in the presence of multi-parameter type classes, only upon the presence of functional dependencies or an alternative mechanism that specifies conditions for closing the world, and that may happen when there exist or not unreachable type variables in constraints. The satisfiability trigger condition is then given automatically, by the existence of unreachable variables in constraints, and does not need to be specified by programmers, using an extra mechanism.

Probabilistic query answering over inconsistent databases

This paper presents a framework for querying inconsistent databases in the presence of functional dependencies. Most of the works dealing with the problem of extracting reliable information from inconsistent databases are based on the notion of repair, a minimal set of tuple insertions and deletions which leads the database to a consistent state (called repaired database), and the notion of consistent query answer, a query answer that can be obtained from every repaired database. In this work, both the notion of repair and query answer differ from the original ones. In the presence of functional dependencies, tuple deletions are the only operations that are performed in order to restore the consistency of an inconsistent database. However, deleting a tuple to remove an integrity violation potentially eliminates useful information in that tuple. In order to cope with this problem, we adopt a notion of repair, based on tuple updates, which allows us to better preserve information in the source database. A drawback of the notion of consistent query answer is that it does not allow us to discriminate among non-consistent answers, namely answers which can be obtained from a non-empty proper subset of the repaired databases. To obtain more informative query answers, we propose the notion of probabilistic query answer, that is query answers are tuples associated with probabilities. This new semantics of query answering over inconsistent databases allows us to give a measure of uncertainty to query answers. We show that the problem of computing probabilistic query answers is FP #P -complete. We also propose a technique for computing probabilistic answers to arbitrary relational algebra queries.

MIRSOFT: mediator for integrating and reconciling sources using ontological functional dependencies

Providing automatic integration solutions is the key to the success of applications managing massive amounts of data. Two main problems stand out in the major studies: (i) the management of the source heterogeneity; (ii) the reconciliation of query results. To tackle the first problem, formal ontologies are used to explicit the semantic of data. The reconciliation problem consists in deciding whether different identifiers refer to the same instance. Two main trends emerge in the reconciliation process: (i) the assumption that different source entities representing the same concept have the same key – a strong hypothesis that violates the autonomy of sources; (ii) The use of statistical methods that identify affinities between concepts – not suitable for sensitive applications. In this paper, we propose a methodology integrating sources referencing shared domain ontology enriched with functional dependencies (FD). The presence of FD gives more autonomy to sources when choosing their primary keys and allows deriving a reconciliation key for a given query. The methodology is then validated using LUBM.

Inference Document Type (Dtd) From Xml Document: Web Structure Mining

XML is becoming a prevalent format and defacto standard for data exchange in many applications. While traditionally, lots of data are stored and managed in relational databases. There is an urgent need to research some efficient methods to convert these data stored in relational databases to XML format when integrating and exchanging these data in XML format. The semantics of XML schemas are crucial to design, query, and store XML documents and functional dependencies are very important representations of semantic information of XML schemas. As DTDs are one of the most frequently used schemas for XML documents in these days, we will use DTDs as schemas of XML documents here. This paper studies the problem of schema conversion from relational schemas to XML DTDs. As functional dependencies play an important role in the schema conversion process, the concept of functional dependency for XML DTDs is used to preserve the semantics implied by functional dependencies and keys of relational schemas. A conversion method is proposed to convert relational schemas to XML DTDs in the presence of functional dependencies, keys and foreign keys. The methods presented here can preserve the semantics implied by functional dependencies, keys and foreign keys of relational schemas and can convert multiple relational tables to XML DTDs at the same time.

Answering constraint-based mining queries on itemsets using previous materialized results

In recent years, researchers have begun to study inductive databases, a new generation of databases for leveraging decision support applications. In this context, the user interacts with the DBMS using advanced, constraint-based languages for data mining where constraints have been specifically introduced to increase the relevance of the results and, at the same time, to reduce its volume. In this paper we study the problem of mining frequent itemsets using an inductive database. We propose a technique for query answering which consists in rewriting the query in terms of union and intersection of the result sets of other queries, previously executed and materialized. Unfortunately, the exploitation of past queries is not always applicable. We then present sufficient conditions for the optimization to apply and show that these conditions are strictly connected with the presence of functional dependencies between the attributes involved in the queries. We show some experiments on an initial prototype of an optimizer which demonstrates that this approach to query answering is viable and in many practical cases it drastically reduces the query execution time.

Justification for inclusion dependency normal form

Functional dependencies (FDs) and inclusion dependencies (INDs) are the most fundamental integrity constraints that arise in practice in relational databases. In this paper, we address the issue of normalization in the presence of FDs and INDs and, in particular, the semantic justification for an inclusion dependency normal form (IDNF), which combines the Boyce-Codd normal form with the restriction on the INDs that they be noncircular and key-based. We motivate and formalize three goals of database design in the presence of FDs and INDs: noninteraction between FDs and INDs, elimination of redundancy and update anomalies, and preservation of entity integrity. We show that (as for FDs), in the presence of INDs, being free of redundancy is equivalent to being free of update anomalies. Then, for each of these properties, we derive equivalent syntactic conditions on the database design. Individually, each of these syntactic conditions is weaker than IDNF and the restriction that an FD is not embedded in the right-hand side of an IND is common to three of the conditions. However, we also show that, for these three goals of database design to be satisfied simultaneously, IDNF is both a necessary and a sufficient condition.

Optimization of a subclass of conjunctive queries

The optimization problem for a subclass of conjunctive queries which is formed by the union of the class of fan-out free queries and a subclass of typed fan-out queries is investigated. The typed fan-out queries in this class are obtained from simple tableaux by allowing atmost one attribute to violate the simple-tablau property. The optimization problem for several restricted subsets of typed fan-out queries is already known to be NP-hard. It is shown that the queries under consideration possess several useful properties which are then used to obtain an O(n 2) optimization algorithm based on the implication graph technique. The optimization of typed fan-out queries, obtained from simple tableaux by allowing atmost two attributes to violate the simple tableau property, is shown to be NP-hard. The optimization of simple tableaux in the presence of functional dependencies is also investigated and is shown to be NP-hard.