1,808 research outputs found

    Implementing β-Reduction by Hypergraph Rewriting

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    AbstractThe aim of this paper is to implement the β-reduction in the lambda;-calculus with a hypergraph rewriting mechanism called collapsed lambda;-tree rewriting. It turns out that collapsed lambda;-tree rewriting is sound with respect to β-reduction and complete with respect to the Gross-Knuth strategy. As a consequence, there exists a normal form for a collapsed lambda;-tree if and only if there exists a normal form for the represented λ-term.I am grateful to Renate Klempien-Hinrichs, Detlef Plump, and to the referees for their helpful comments

    Dependently-Typed Formalisation of Typed Term Graphs

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    We employ the dependently-typed programming language Agda2 to explore formalisation of untyped and typed term graphs directly as set-based graph structures, via the gs-monoidal categories of Corradini and Gadducci, and as nested let-expressions using Pouillard and Pottier's NotSoFresh library of variable-binding abstractions.Comment: In Proceedings TERMGRAPH 2011, arXiv:1102.226

    A Graph-Based Semantics Workbench for Concurrent Asynchronous Programs

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    A number of novel programming languages and libraries have been proposed that offer simpler-to-use models of concurrency than threads. It is challenging, however, to devise execution models that successfully realise their abstractions without forfeiting performance or introducing unintended behaviours. This is exemplified by SCOOP---a concurrent object-oriented message-passing language---which has seen multiple semantics proposed and implemented over its evolution. We propose a "semantics workbench" with fully and semi-automatic tools for SCOOP, that can be used to analyse and compare programs with respect to different execution models. We demonstrate its use in checking the consistency of semantics by applying it to a set of representative programs, and highlighting a deadlock-related discrepancy between the principal execution models of the language. Our workbench is based on a modular and parameterisable graph transformation semantics implemented in the GROOVE tool. We discuss how graph transformations are leveraged to atomically model intricate language abstractions, and how the visual yet algebraic nature of the model can be used to ascertain soundness.Comment: Accepted for publication in the proceedings of FASE 2016 (to appear

    Scalable Semantic Matching of Queries to Ads in Sponsored Search Advertising

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    Sponsored search represents a major source of revenue for web search engines. This popular advertising model brings a unique possibility for advertisers to target users' immediate intent communicated through a search query, usually by displaying their ads alongside organic search results for queries deemed relevant to their products or services. However, due to a large number of unique queries it is challenging for advertisers to identify all such relevant queries. For this reason search engines often provide a service of advanced matching, which automatically finds additional relevant queries for advertisers to bid on. We present a novel advanced matching approach based on the idea of semantic embeddings of queries and ads. The embeddings were learned using a large data set of user search sessions, consisting of search queries, clicked ads and search links, while utilizing contextual information such as dwell time and skipped ads. To address the large-scale nature of our problem, both in terms of data and vocabulary size, we propose a novel distributed algorithm for training of the embeddings. Finally, we present an approach for overcoming a cold-start problem associated with new ads and queries. We report results of editorial evaluation and online tests on actual search traffic. The results show that our approach significantly outperforms baselines in terms of relevance, coverage, and incremental revenue. Lastly, we open-source learned query embeddings to be used by researchers in computational advertising and related fields.Comment: 10 pages, 4 figures, 39th International ACM SIGIR Conference on Research and Development in Information Retrieval, SIGIR 2016, Pisa, Ital

    Context-free tree grammars are as powerful as context-free jungle grammars

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    Jungles generalize trees by sharing subtrees and allowing garbage. It is shown that IO context-free tree grammars generate the same jungle languages as context-free jungle grammars. Also, they define the same subsets of any algebra

    Context-Free Tree Grammars are as Powerful as Context-Free Jungle Grammars

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    Critical Pairs in Term Graph Rewriting

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    Modular Termination of Graph Transformation

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    Meta-Modeling And Structural Paradigm For Strategic Alignment Of Information System

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    The information system is strongly sensitive to strategic evolutions of the enterprise: organisational change, change of objectives, modified variety, new objects and business processes, etc. With the objective to control strategic alignment of information systems, we propose an approach based on our extended enterprise meta-model ISO/DSI 19440. This extension is borrowed from the COBIT framework for IT processes. In order to better lead evolutions of the information system, this extension integrates necessary structures for developing systemic tools, based on a structural paradigm. In this work we propose to build an extension of the meta-model ISO 19440, so that we can explicitly bring the issue of alignment of various aspects of the information system. The strengths of the strategic alignment are interactions and couplings between different views of the meta-model: the interaction between activities and resources, the linkage between business processes and activities, the resource interdependence of entities and objects of the enterprise, the coupling between the capabilities and resources, etc. We propose to use the COBIT best practices for driving IT processes. Thus we add the abstract concept objective which will be specialized. We will also add a specialization of functional entity to model IT processes. In this work, we also offer a variety of algebraic structures to establish structural measures on the information system. For each class of structure we define its role and contribution to the governance of the information system
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