Inheritance hierarchies: Semantics and unification

Inheritance hierarchies are introduced as a means of representing taxonomicallyorganized data. The hierarchies are built up from so-called feature types that are ordered by subtyping and whose elements are records. Every feature type comes with a set of features prescribing fields of its record elements. So-called feature terms are available to denote subsets of feature types. Feature unification is introduced as an operation that decides whether two feature terms have a nonempty intersection and computes a feature term denoting the intersection.We model our inheritance hierarchies as algebraic specifications in ordersortedequational logic using initial algebra semantics. Our framework integrates feature types whose elements are obtained as records with constructor types whose elements are obtained by constructor application. Unification in these hierarchies combines record unification with order-sorted term unification and is presented as constraint solving. We specify a unitary unification algorithm by a set of simplification rules and prove its soundness and completeness with respect to the model-theoretic semantics

A Database Interface for Complex Objects

We describe a formal design for a logical query language using psi-terms as data structures to interact effectively and efficiently with a relational database. The structure of psi-terms provides an adequate representation for so-called complex objects. They generalize conventional terms used in logic programming: they are typed attributed structures, ordered thanks to a subtype ordering. Unification of psi-terms is an effective means for integrating multiple inheritance and partial information into a deduction process. We define a compact database representation for psi-terms, representing part of the subtyping relation in the database as well. We describe a retrieval algorithm based on an abstract interpretation of the psi-term unification process and prove its formal correctness. This algorithm is efficient in that it incrementally retrieves only additional facts that are actually needed by a query, and never retrieves the same fact twice

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

A LATTICE THEORETIC APPROACH TO COMPUTATION BASED ON A CALCULUS OF PARTIALLY ORDERED TYPE STRUCTURES (PROPERTY INHERITANCE, SEMANTIC NETS, GRAPH UNIFICATION)

The purpose of this thesis is twofold: (1) to define a formal lattice-theoretic calculus of partially ordered type structures where the ordering is meant to reflect subtyping; (2) to propose a model of computation which amounts to solving systems of simultaneous equations in a lattice of types. The specific contributions which I believe to be original of the research presented here are: (1) An extrapolation of the syntactic properties of first-order terms to provide insight in formalizing record-like type structures; (2) A simple type-as-set semantics and a motivational discussion of what this entails for the operational use of partially ordered types in programming; (3) A lattice-theoretic calculus of type subsumption and a formal universal construction extending this calculus in the light of the foregoing discussion; (4) An efficient algorithm to compute greatest lower bounds of type structures; (5) The definition of a particular language (KBL) based on solving recursive equations in the lattice of types, and a fixed-point semantics study of its model of computation

A LATTICE THEORETIC APPROACH TO COMPUTATION BASED ON A CALCULUS OF PARTIALLY ORDERED TYPE STRUCTURES (PROPERTY INHERITANCE, SEMANTIC NETS, GRAPH UNIFICATION)

The purpose of this thesis is twofold: (1) to define a formal lattice-theoretic calculus of partially ordered type structures where the ordering is meant to reflect subtyping; (2) to propose a model of computation which amounts to solving systems of simultaneous equations in a lattice of types. The specific contributions which I believe to be original of the research presented here are: (1) An extrapolation of the syntactic properties of first-order terms to provide insight in formalizing record-like type structures; (2) A simple type-as-set semantics and a motivational discussion of what this entails for the operational use of partially ordered types in programming; (3) A lattice-theoretic calculus of type subsumption and a formal universal construction extending this calculus in the light of the foregoing discussion; (4) An efficient algorithm to compute greatest lower bounds of type structures; (5) The definition of a particular language (KBL) based on solving recursive equations in the lattice of types, and a fixed-point semantics study of its model of computation

LIFE - A Natural Language for Natural Language

Experimenting with formalisms for Natural Language Processing involves costly programming overhead in conventional computing idioms, even as &quot;advanced&quot; as Lisp or Prolog. LIFE is a programming language which incorporates an elegant type system which supports a powerful facility for structured type inheritance. Also, LIFE reconciles styles from Functional Programming and Logic Programming by implicitly delegating control to an automatic suspension mechanism. This allows interleaving interpretation of relational and functional expressions which specify abstract structural dependencies on objects. Together, these features provide a convenient and versatile power of abstraction for very high-level expression of constrained data structures. Computational linguistics is a discipline where such abstractions are particularly useful. Therefore, obvious convenience is offered by LIFE for experimentation to the computational linguist, who becomes relieved from burdensome yet extrinsic programming..

Entailment and Disentailment of Order-Sorted Feature Constraints

LIFE uses matching on order-sorted feature structures for passing arguments to functions. As opposed to unification which amounts to normalizing a conjunction of constraints, solving a matching problem consists of deciding whether a constraint (guard) or its negation are entailed by the context. We give a complete and consistent set of rules for entailment and disentailment of order-sorted feature constraints. These rules are directly usable for relative simplification, a general proof-theoretic method for proving guards in concurrent constraint logic languages using guarded rules. 1 Introduction LIFE [5, 4] extends the computational paradigm of Logic Programming in two essential ways: ffl using a data structure richer than that provided by first-order constructor terms; and, ffl allowing interpretable functional expressions as bona fide terms. The first extension is based on /-terms which are attributed partially-ordered sorts denoting sets of objects [1, 2]. In particular, /-terms..

Order-Sorted Feature Theory Unification

Order-sorted feature (OSF) terms provide an adequate representation for objects as flexible records. They are sorted, attributed, possibly nested, structures, ordered thanks to a subsort ordering. Sort definitions offer the functionality of classes imposing structural constraints on objects. These constraints involve variable sorting and equations among feature paths, including self-reference. Formally, sort definitions may be seen as axioms forming an OSF theory. OSF theory unification is the process of normalizing an OSF term, using sort-unfolding to enforce structural constraints imposed on sorts by their definitions. It allows objects to inherit, and thus abide by, constraints from their classes. A formal system is thus obtained that logically models record objects with recursive class definitions accommodating multiple inheritance. We show that OSF theory unification is undecidable in general. However, we propose a set of confluent normalization rules which is complete for detecting inconsistency of an object with respect to an OSF theory. These rules translate into an efficient algorithm using structure-sharing and lazy constraint-checking. Furthermore, a subset consisting of all rules but one is confluent and terminating. This yields a practical complete normalization strategy, as well as an effective compilation scheme