Query Containment for Highly Expressive Datalog Fragments

The containment problem of Datalog queries is well known to be undecidable. There are, however, several Datalog fragments for which containment is known to be decidable, most notably monadic Datalog and several "regular" query languages on graphs. Monadically Defined Queries (MQs) have been introduced recently as a joint generalization of these query languages. In this paper, we study a wide range of Datalog fragments with decidable query containment and determine exact complexity results for this problem. We generalize MQs to (Frontier-)Guarded Queries (GQs), and show that the containment problem is 3ExpTime-complete in either case, even if we allow arbitrary Datalog in the sub-query. If we focus on graph query languages, i.e., fragments of linear Datalog, then this complexity is reduced to 2ExpSpace. We also consider nested queries, which gain further expressivity by using predicates that are defined by inner queries. We show that nesting leads to an exponentially increasing hierarchy for the complexity of query containment, both in the linear and in the general case. Our results settle open problems for (nested) MQs, and they paint a comprehensive picture of the state of the art in Datalog query containment.Comment: 20 page

Querying Schemas With Access Restrictions

We study verification of systems whose transitions consist of accesses to a Web-based data-source. An access is a lookup on a relation within a relational database, fixing values for a set of positions in the relation. For example, a transition can represent access to a Web form, where the user is restricted to filling in values for a particular set of fields. We look at verifying properties of a schema describing the possible accesses of such a system. We present a language where one can describe the properties of an access path, and also specify additional restrictions on accesses that are enforced by the schema. Our main property language, AccLTL, is based on a first-order extension of linear-time temporal logic, interpreting access paths as sequences of relational structures. We also present a lower-level automaton model, Aautomata, which AccLTL specifications can compile into. We show that AccLTL and A-automata can express static analysis problems related to "querying with limited access patterns" that have been studied in the database literature in the past, such as whether an access is relevant to answering a query, and whether two queries are equivalent in the accessible data they can return. We prove decidability and complexity results for several restrictions and variants of AccLTL, and explain which properties of paths can be expressed in each restriction.Comment: VLDB201

Measurement of triple differential photon plus jet cross section by D0

We report on a new measurement of triple differential cross section for the process ppbar -> photon + jet + X in ppbar collisions at sqrt(s)=1.96 TeV by the D0 Collaboration at Fermilab based on a dataset corresponding to an integrated luminosity of 1.1 fb-1.Comment: 3 pages, 1 figure, To appear in the Proceedings of the 2007 Europhysics Conference on High Energy Physics, Manchester, UK. Accepted for publication in Journal of Physics : Conference Serie

Evaluating Datalog via Tree Automata and Cycluits

We investigate parameterizations of both database instances and queries that make query evaluation fixed-parameter tractable in combined complexity. We show that clique-frontier-guarded Datalog with stratified negation (CFG-Datalog) enjoys bilinear-time evaluation on structures of bounded treewidth for programs of bounded rule size. Such programs capture in particular conjunctive queries with simplicial decompositions of bounded width, guarded negation fragment queries of bounded CQ-rank, or two-way regular path queries. Our result is shown by translating to alternating two-way automata, whose semantics is defined via cyclic provenance circuits (cycluits) that can be tractably evaluated.Comment: 56 pages, 63 references. Journal version of "Combined Tractability of Query Evaluation via Tree Automata and Cycluits (Extended Version)" at arXiv:1612.04203. Up to the stylesheet, page/environment numbering, and possible minor publisher-induced changes, this is the exact content of the journal paper that will appear in Theory of Computing Systems. Update wrt version 1: latest reviewer feedbac

Next-To-Leading Order Determination of Fragmentation Functions

We analyse LEP and PETRA data on single inclusive charged hadron cross-sections to establish new sets of Next-to-Leading order Fragmentation Functions. Data on hadro-production of large-$p_{\bot}$ hadrons are also used to constrain the gluon Fragmentation Function. We carry out a critical comparison with other NLO parametrizations

Utilization of tmRNA sequences for bacterial identification

In recent years, molecular approaches based on nucleotide sequences of ribosomal RNA (rRNA) have become widely used tools for identification of bacteria [1-4]. The high degree of evolutionary conservation makes 16S and 23S rRNA molecules very suitable for phylogenetic studies above the species level [3-5]. More than 16,000 sequences of 16S rRNA are presently available in public databases [4,6]. The 16S rRNA sequences are commonly used to design fluorescently labeled oligonucleotide probes. Fluorescence in situ hybridization (FISH) with these probes followed by observation with epifluorescence microscopy allows the identification of a specific microorganism in a mixture with other bacteria [2-4]. By shifting probe target sites from conservative to increasingly variable regions of rRNA, it is possible to adjust the probe specificity from kingdom to species level. Nevertheless, 16S rRNA sequences of closely related strains, subspecies, or even of different species are often identical and therefore can not be used as differentiating markers [3]. Another restriction concerns the accessibility of target sites to the probe in FISH experiments. The presence of secondary structures, or protection of rRNA segments by ribosomal proteins in fixed cells can limit the choice of variable regions as in situ targets for oligonucleotide probes [7,8]. One way to overcome the limitations of in situ identification of bacteria is to use molecules other than rRNA for phylogenetic identification of bacteria, for which nucleotide sequences would be sufficiently divergent to design species specific probes, and which would be more accessible to oligonucleotide probes. For this purpose we investigated the possibility of using tmRNA (also known as 10Sa RNA; [9-11]). This molecule was discovered in E. coli and described as small stable RNA, present at ~1,000 copies per cell [9,11]. The high copy number is an important prerequisite for FISH, which works best with naturally amplified target molecules. In E. coli, tmRNA is encoded by the ssrA gene, is 363 nucleotides long and has properties of tRNA and mRNA [12,13]. tmRNA was shown to be involved in the degradation of truncated proteins: the tmRNA associates with ribosomes stalled on mRNAs lacking stop codons, finally resulting in the addition of a C-terminal peptide tag to the truncated protein. The peptide tag directs the abnormal protein to proteolysis [14,15]. 165 tmRNA sequences have so far (August 2001; The tmRNA Website: http://www.indiana.edu/~tmrna/) been determined [16,17]. The tmRNA is likely to be present in all bacteria and has also been found in algae chloroplasts, the cyanelle of Cyanophora paradoxa and the mitochondrion of the flagellate Reclinomonas americana[10,17,18]

Beyond Work-Family Balance: Are Family-Friendly Organizations More Attractive?

In a context of labour shortage, organizations face immense pressures to attract the best employees, and therefore deploy great efforts to increase their organizational attractiveness. In order to appeal to working women or younger workers, some organizations have implemented policies designed to balance work and family. Yet, the effect of such family-friendly practices (FFPs) on organizational attractiveness has seldom been investigated; this study endeavours to fill this gap.The literature review led us to posit that organizations that have implemented FFPs are more attractive to applicants (H1). However, this main effect may be moderated by desire for segmentation (H2). Role segmentation refers to the separation of personal and professional roles, while role integration designates the blurring of boundaries between roles. For example, individuals with a high level of desire for segmentation may be more attracted to companies that offer segmentation strategies (e.g., flexible scheduling) than to companies that offer integration practices (e.g., telecommuting). Finally, the effect of corporate reputation is also tested (H3).Using a policy-capturing research design, we tested the distinct effect of four FFPs (on-site child care; generous personal leaves; flexible scheduling; teleworking) on applicant attraction as well as the effects of organizational reputation and candidates’ desire for segmentation. Our results indicate that FFPs do have a main effect on attractiveness. More specifically, the two scenarios that received the highest scores on attractiveness were personal leaves and flexible scheduling. Contrary to expectations, we did not find a significant “Desire for segmentation x Family-friendly practices” interaction. However, the results reveal a significant three-way interaction, which indicates that the anticipated Desire for segmentation x Family-friendly practices is significant for some values of the reputation variable. As expected, corporate reputation does have a significant main effect on attractiveness. The implications of this study are discussed in conclusion.Dans un contexte de rareté de main-d’oeuvre, les organisations sont soumises à des pressions grandissantes pour attirer des employés de talents. Se préoccupant de leur capacité d’attraction, notamment auprès des femmes et des jeunes professionnels, de plus en plus d’entreprises proposent à leurs employés une gamme de pratiques visant à favoriser la conciliation travail-famille, tels des horaires flexibles ou des garderies en milieu de travail.Bien que l’effet de ces pratiques n’ait pas été beaucoup testé empiriquement, une recension des écrits nous a permis de postuler que les organisations qui offrent de telles pratiques seront effectivement plus attrayantes aux yeux des candidats (H1), mais que cet effet sera modéré par le désir de segmentation (H2). Ce concept réfère à la séparation entre les rôles professionnels et personnels. Ainsi, les individus ayant un désir de segmentation élevé seront plus attirés par des compagnies qui offrent des stratégies de conciliation travail-famille basées sur la séparation des rôles, comme les horaires flexibles, plutôt que des stratégies basées sur l’intégration des rôles, comme le télétravail. La réputation de l’organisation a également un effet sur son pouvoir d’attraction (H3).Utilisant une méthode de recherche par scénario, nous avons testé l’effet individuel de quatre pratiques de conciliation sur l’attraction de candidats : service de garde sur les lieux du travail, généreux congés personnels, horaires flexibles et télétravail. Nos résultats confirment que les pratiques de conciliation ont un effet sur l’attraction. Plus spécifiquement, les scénarios ayant obtenu les scores d’attraction les plus élevés sont ceux qui proposaient des congés personnels généreux et la flexibilité des horaires. Contrairement à nos attentes, l’interaction « besoin de segmentation x pratiques de conciliation » ne s’est pas révélée significative. Tel qu’attendu, la réputation de l’entreprise a un effet principal significatif sur l’attraction. Les implications de ces résultats pour la recherche et la pratique sont présentées en conclusion.En un contexto de escasez de mano de obra, las organizaciones son sometidas a presiones cada vez más grandes para atraer empleados de talento. Las organizaciones se preocupan de su capacidad de atracción, sobre todo respecto a las mujeres y los jóvenes profesionales, y cada vez mas las empresas proponen a sus empleados una gama de prácticas con miras a favorecer la conciliación trabajo-familia, como los horarios flexibles o las guarderías en el lugar de trabajo.Aunque el efecto de estas prácticas ha sido poco evaluada empíricamente, una recensión de escritos nos ha permitido de postular que las organizaciones que ofrecen tales prácticas serán efectivamente más atractivas a la vista de los candidatos (H1), pero que este efecto será moderado por el deseo de segmentación (H2). Este concepto hace referencia a la separación entre los roles profesionales y personales. Así, los individuos que tienen un deseo de segmentación elevado serán más atraídos por las compañías que ofrecen estrategias de conciliación trabajo-familia basadas en la separación de roles, como los horarios flexibles, en vez de las estrategias basadas sobre la integración de roles, como el teletrabajo. La reputación de la organización tiene también un efecto sobre su poder de atracción (H3). Utilizando un método de investigación por escenario, hemos evaluado el efecto individual de cuatro prácticas de conciliación (servicio de guardería en el lugar de trabajo, permisos personales generosos, horarios flexibles, teletrabajo) sobre la atracción de candidatos. Nuestros resultados confirman que las prácticas de conciliación tienen un efecto sobre la atracción. Más específicamente, los escenarios que han obtenido los puntajes de atracción más elevados son aquellos que proponen permisos personales generosos y flexibilidad de horarios. Contrariamente a nuestras previsiones, la interacción entre la necesidad de segmentación y las prácticas de conciliación no se reveló significativa. Tal como previsto, la reputación de la empresa tiene un efecto principal significativo sobre la atracción. Las implicaciones de estos resultados para la investigación y la práctica son presentadas en conclusión