The Constructive method for query containment checking (extended version)

We present a new method that checks Query Containment for queries with negated derived atoms and/or integrity constraints. Existing methods for Query Containment checking that deal with these cases do not check actually containment but another related property called uniform containment, which is a sufficient but not necessary condition for containment. Our method can be seen as an extension of the canonical databases approach beyond the class of conjunctive queries.Postprint (published version

Dels materials clàssics als alternatius en la preparació de substrats. Motivacions de la substitució, tendències, disponibilitat i característiques

En el context hortícola, el terme substrat s’aplica a qualsevol material sòlid, diferent del sòl insitu, natural o artificial, pur o en barreja, que col·locat en un contenidor i sotmès a un programa específic de gestió (principalment reg i fertilització) permet l’establiment de l’aparell radicular amb un grau d’aeració satisfactori, possibilita una adequada nutrició hídrica i mineral i actua com a suport de la planta.Postprint (published version

Distance-layer structure of the De Bruijn and Kautz digraphs: analysis and application to deflection routing

This is the peer reviewed version of the following article: Fàbrega, J.; Martí, J.; Muñoz, X. Distance-layer structure of the De Bruijn and Kautz digraphs: analysis and application to deflection routing. "Networks", 29 Juliol 2023, which has been published in final form at https://onlinelibrary.wiley.com/doi/10.1002/net.22177. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.In this article, we present a detailed study of the reach distance-layer structure of the De Bruijn and Kautz digraphs, and we apply our analysis to the performance evaluation of deflection routing in De Bruijn and Kautz networks. Concerning the distance-layer structure, we provide explicit polynomial expressions, in terms of the degree of the digraph, for the cardinalities of some relevant sets of this structure. Regarding the application to defection routing, and as a consequence of our polynomial description of the distance-layer structure, we formulate explicit expressions, in terms of the degree of the digraph, for some probabilities of interest in the analysis of this type of routing. De Bruijn and Kautz digraphs are fundamental examples of digraphs on alphabet and iterated line digraphs. If the topology of the network under consideration corresponds to a digraph of this type, we can perform, in principle, a similar vertex layer description.Partially supported by the Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación, Spain, and the European Regional Development Fund under project PGC2018-095471-B-I00; and by AGAUR from the Catalan Government under project 2017SGR-1087.Peer ReviewedPostprint (author's final draft

Grid design benchmark on sheets with nonzero thickness

The conventional scattering analysis of perfectly conducting sheets ignores the scattering contribution of the rim. The so-called thin-surface scheme arises from the discretization of the Electric-field Integral Equation by assuming the sheet thickness to be null. This gives rise to many less unknowns than the full approach, arising from modelling the whole plate. Although good accuracy is observed in many practical applications, the thin-plate scattering analysis of thick enough sheets, especially under oblique incidences, with low grazing angles, exhibits great inaccuracies. A recent approach, so-called thick-surface, has proved to show similar accuracy as the full scheme, also in those cases where the thin-surface scheme fails, with moderate computational effort. In this paper, we show RCS results computed with the thick-surface approach for several sheets with nonzero thickness where the thin-surface scheme fails. Several types of meshes are adopted, triangular, quadrangular or hybrid. The required symmetries for the generation of the meshes are pointed out in each case

Monte Carlo methods in electromagnetic scattering computations

The solution of the electromagnetic scattering problem by the Method of Moments often leads to huge systems of equations that require large computational resources. In parallel computing environments, communication between computing units constitute the main bottleneck that limits the scalability of the problem. In this work, we use randomized techniques to relax the need for communication, thus achieving better scalability. The method is based on a formal solution of the scattering problem as a Neumann series modified by a set of coefficients who ensure its convergence. In the case of the Volume Integral Equation for dielectric objects, these coefficients are obtained by a conformal transformation that depends on the spectrum of the scattering operator, which is known to be confined in a certain region of the complex plane thanks to the spectral localization theorem. Then, the terms of the Neumann series are approximated by randomly sampling elements of its matrix representation computed by the method of moments. We show that this estimator is unbiased and, unlike other Monte Carlo techniques based on the Neumann series, always converges to the solution. The main advantages of this method are its ease of formulation and its potential parallelism. Since the coefficients of the modified Neumann series are known beforehand, the Monte Carlo samples can be computed independently without the need of communication between different processors or computing units, apart from a final reduction operation. Thus, the method is scalable and well suited for highly parallel architectures. Besides, the granularity of the parallel method can be adapted in a versatile way to exploit the capabilities of a particular computational environment

Experimental Models to Study End-Organ Morbidity in Sleep Apnea: Lessons Learned and Future Directions.

Sleep apnea (SA) is a very prevalent sleep breathing disorder mainly characterized by intermittent hypoxemia and sleep fragmentation, with ensuing systemic inflammation, oxidative stress, and immune deregulation. These perturbations promote the risk of end-organ morbidity, such that SA patients are at increased risk of cardiovascular, neurocognitive, metabolic and malignant disorders. Investigating the potential mechanisms underlying SA-induced end-organ dysfunction requires the use of comprehensive experimental models at the cell, animal and human levels. This review is primarily focused on the experimental models employed to date in the study of the consequences of SA and tackles 3 different approaches. First, cell culture systems whereby controlled patterns of intermittent hypoxia cycling fast enough to mimic the rates of episodic hypoxemia experienced by patients with SA. Second, animal models consisting of implementing realistic upper airway obstruction patterns, intermittent hypoxia, or sleep fragmentation such as to reproduce the noxious events characterizing SA. Finally, human SA models, which consist either in subjecting healthy volunteers to intermittent hypoxia or sleep fragmentation, or alternatively applying oxygen supplementation or temporary nasal pressure therapy withdrawal to SA patients. The advantages, limitations, and potential improvements of these models along with some of their pertinent findings are reviewed

Validation of schema mappings with nested queries

With the emergence of the Web and the wide use of XML for representing data, the ability to map not only flat relational but also nested data has become crucial. The design of schema mappings is a semi-automatic process. A human designer is needed to guide the process, choose among mapping candidates, and successively refine the mapping. The designer needs a way to figure out whether the mapping is what was intended. Our approach to mapping validation allows the designer to check whether the mapping satisfies certain desirable properties. In this paper, we focus on the validation of mappings between nested relational schemas, in which the mapping assertions are either inclusions or equalities of nested queries. We focus on the nested relational setting since most XML’s Document Type Definitions (DTDs) can be represented in this model. We perform the validation by reasoning on the schemas and mapping definition. We take into account the integrity constraints defined on both the source and target schema.Preprin

A schema-only approach to validate XML schema mappings

Since the emergence of the Web, the ability to map XML data between different data sources has become crucial. Defining a mapping is however not a fully automatic process. The designer needs to figure out whether the mapping is what was intended. Our approach to this validation consists of defining and checking certain desirable properties of mappings. We translate the XML schemas and the mapping into first-order logic formalism and apply a reasoning mechanism to check the desirable properties automatically, without assuming any particular instantiation of the schemas.Preprin

Testing Termination of Query Satisfiability Checking on Expressive Database Schemas

A query is satisfiable if there is at least one consistent instance of the database in which it has a non-empty answer. Defining queries on a database schema and checking their satisfiability can help the database designer to be sure whether the produced database schema is what was intended. The formulation of such queries may easily require the use of some arithmetic comparisons or negated expressions. Unfortunately, checking the satisfiability of this class of queries on a database schema that most likely have some integrity constraints (e.g., keys, foreign keys, Boolean checks) is, in general, undecidable. However, although the problem is undecidable for such a class of schemas and queries, it may not be so for a particular query satisfiability check. In this paper, we propose to perform a termination test as a previous step to query satisfiability checking. If positive, the termination test guarantees that the corresponding query satisfiability check will terminate. We assume the CQC method is the underlying query satisfiability checking method; to the best of our knowledge, it is the only method of this kind able to deal with schemas and queries as expressive as the ones we consider.Preprin