148 research outputs found

    Caterpillar dualities and regular languages

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    We characterize obstruction sets in caterpillar dualities in terms of regular languages, and give a construction of the dual of a regular family of caterpillars. We show that these duals correspond to the constraint satisfaction problems definable by a monadic linear Datalog program with at most one EDB per rule

    Regular families of forests, antichains and duality pairs of relational structures

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    Homomorphism duality pairs play crucial role in the theory of relational structures and in the Constraint Satisfaction Problem. The case where both classes are finite is fully characterized. The case when both side are infinite seems to be very complex. It is also known that no finite-infinite duality pair is possible if we make the additional restriction that both classes are antichains. In this paper we characterize the infinite-finite antichain dualities and infinite-finite dualities with trees or forest on the left hand side. This work builds on our earlier papers that gave several examples of infinite-finite antichain duality pairs of directed graphs and a complete characterization for caterpillar dualities

    On infinite-finite duality pairs of directed graphs

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    The (A,D) duality pairs play crucial role in the theory of general relational structures and in the Constraint Satisfaction Problem. The case where both classes are finite is fully characterized. The case when both side are infinite seems to be very complex. It is also known that no finite-infinite duality pair is possible if we make the additional restriction that both classes are antichains. In this paper (which is the first one of a series) we start the detailed study of the infinite-finite case. Here we concentrate on directed graphs. We prove some elementary properties of the infinite-finite duality pairs, including lower and upper bounds on the size of D, and show that the elements of A must be equivalent to forests if A is an antichain. Then we construct instructive examples, where the elements of A are paths or trees. Note that the existence of infinite-finite antichain dualities was not previously known

    On Ramsey properties of classes with forbidden trees

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    Let F be a set of relational trees and let Forbh(F) be the class of all structures that admit no homomorphism from any tree in F; all this happens over a fixed finite relational signature σ\sigma. There is a natural way to expand Forbh(F) by unary relations to an amalgamation class. This expanded class, enhanced with a linear ordering, has the Ramsey property.Comment: Keywords: forbidden substructure; amalgamation; Ramsey class; partite method v2: changed definition of expanded class; v3: final versio

    Homogeneity and Homogenizability: Hard Problems for the Logic SNP

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    We show that the question whether a given SNP sentence defines a homogenizable class of finite structures is undecidable, even if the sentence comes from the connected Datalog fragment and uses at most binary relation symbols. As a byproduct of our proof, we also get the undecidability of some other properties for Datalog programs, e.g., whether they can be rewritten in MMSNP, whether they solve some finite-domain CSP, or whether they define the age of a reduct of a homogeneous Ramsey structure in a finite relational signature. We subsequently show that the closely related problem of testing the amalgamation property for finitely bounded classes is EXPSPACE-hard or PSPACE-hard, depending on whether the input is specified by a universal sentence or a set of forbidden substructures.Comment: 34 pages, 3 figure

    Adding Pebbles to Weighted Automata: Easy Specification & Efficient Evaluation

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    International audienceWe extend weighted automata and weighted rational expressions with 2-way moves and reusable pebbles. We show with examples from natural language modeling and quantitative model-checking that weighted expressions and automata with pebbles are more expressive and allow much more natural and intuitive specifications than classical ones. We extend Kleene–Schützenberger theorem showing that weighted expressions and automata with pebbles have the same expressive power. We focus on an efficient translation from expressions to automata. We also prove that the evaluation problem for weighted automata can be done very efficiently if the number of reusable pebbles is low

    Practitioner Experiences of Forest School

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    The aim of this thesis is to investigate the situated subjectivities of the experiences of Forest School (FS) practitioners, in their journeys from training to initial practice. The research explores the impact of FS training, environmental and socio-cultural influences upon the practitioners and how their practices adapt in context. Eight in-depth case studies of FS trainee practitioners were undertaken over a period of two years (2010-12) using multiple qualitative methods. The analysis is in three parts; on practitioner identities, approaches and contexts. The thesis contributes three new conceptual models to outdoor pedagogical research. The concept of eco-social identity frames the ongoing construction of self. The FS adult role is theorised as a connector, engaged in dynamic role processes. The analysis of practitioner approaches in context uses Shared Space; an ecosystemic frame of practice and agency. Further analysis of practitioners’ experience of team contexts draws on theoretical lenses on role, socialisation and norms from Goffman and Foucault. Team relationships became positioned in either conflict, collaboration or congruence. The study contributes new insights into the impact of FS training and the influence of socialisation and subjectivity in the application of outdoor pedagogy. Early life experience, nature-society relations, and passionate purpose motivated the practitioners. Adult-to-adult interaction affected practice outcomes significantly, with strong disparities in setting teams regarding values and ethos, team interest, controls and standards in setting practices, curriculum pressures, setting aims, and site provision and care. The results imply that collaborative partnership and a whole team approach are effective strategies for ongoing practice, and tokenistic practice is a destructive strategy

    'I'm learning nature now with them': what can a holistic perspective contribute to our understanding of the influential relations between young children, adults and a natural environment?

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    There is a contemporary concern about children’s loss of contact with the natural world and its associated benefits. Children’s reduced independent mobility is an influential factor and there is growing recognition of an interdependence between child and adult in accessing outdoor play. This research explores a gap in literature through considering impacts on adults in sharing outdoor experiences with children. A Froebelian holistic perspective has been foregrounded within this due to its understanding of child, adult and natural environment relations according to their mutual benefit. This has been investigated though a suburban preschool’s organization of family trips to local natural environments. Twelve participant families with children between two and four years old have formed the focus of research activity. A sensory ethnography approach has framed use of child-worn Go-Pros™ on trips and this footage has formed the basis for sensory elicitation interviews with adults. Fifteen hours of Go-Pro™ footage have been reviewed along with eleven hours of audio-recorded parent reflections. Analysis of these materials has drawn upon a vocabulary of holistic relations offered by the theory of the evolution of human consciousness (Gebser, 1949). This vocabulary gives equal value to the relational qualities expressed by adult and child (Chawla, 2002) and offers a lens through which to consider Froebelian pedagogical relationships. Findings have highlighted the potential for children to draw adults into immersive sensory experiences, big questions, and storied relations with their immediate surroundings. This can balance an adult potential to draw children towards a capacity for abstract relations with a whole or global context. Each can be considered significant in forming rich, thick, continuous connections between individual and whole and can align with sustainability thinking in a need to act local but think global. Froebelian philosophy may now offer a source of guidance towards an education for sustainable development through a path of familiar early years practices revitalized by a holistic logic

    A dialogic journey into exploring multiliteracies in translation for children and a researcher in international picturebooks

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    In today’s increasingly digitised world, we communicate both locally and globally across different languages, modes and media. Since the New London Group’s (1996) seminal ‘Pedagogy of Multiliteracies’ some twenty years ago, there have been further significant developments in the way we communicate, with the 21st century considered ‘the great age of translation’ (Bassnett 2014:1). Yet despite the increasing number of multilingual, multimodal texts we encounter, classrooms continue to teach traditional, monolingual print-based models of literacy. This research is therefore primarily in response to this rapidly evolving context, with a curiosity as to how international picturebooks might develop the skills learners need to succeed both now and in the future. The research process has been a journey comprising two separate phases of empirical study as I have sought to find out the best way to approach this topic. My initial focus, Phase One, was exploring the visual literacy skills of EAL learners and I completed a project in a primary school in Glasgow. As a result of the emerging findings, the research then changed in two ways – to a whole class approach comprising both bilingual and monolingual learners, and to a focus on translation. Phase Two comprised two whole class projects in the Scottish Borders, with my overarching question: How can translating both the verbal and visual in international picturebooks develop the multiliteracies learners require in the 21st century? In my discussions of multiliteracies, I have focused on four different areas: visual, critical, digital and intercultural literacies. Learners’ visual literacy skills were developed through their recognition of the cultural codes in visuals. Their critical literacies were developed through the recognition of power in texts, through deconstructing and reconstructing texts and seeking multiple perspectives. Digital literacies were improved through the critical retrieval of information online and through using tools such as Google Translate and, like Gilster (1997), I have suggested a key component of digital literacies is having an open mind as to the possibilities of emerging technologies. I also argue that intercultural literacy should be included under the umbrella of multiliteracies, in order to provide learners with the tools to navigate the increasingly multilingual, multicultural spaces they are likely to encounter, and offer tentative findings which show how translating international picturebooks has helped to develop these skills and attitudes. Prior to concluding the thesis, I briefly consider alternative lenses for the research, in particular Critical Race Theory, identity and translingualism. I then sum up the project in Chapter 11 and make some key recommendations, including the need for multiliteracies to be explicitly acknowledged in the curriculum and for international picturebooks, including those in the first languages (L1s) of the bilingual learners, to be introduced into classrooms to challenge the dominance of English and ‘what counts’ as reading. Alongside a discussion as to the limitations of the research and possible future directions, the thesis concludes with a call for both academics and educators to consider how the gap between research and practice might be reduced, to enable research such as this to have an impact on today’s literacy learners
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