19,978 research outputs found

    Archiving the Relaxed Consistency Web

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    The historical, cultural, and intellectual importance of archiving the web has been widely recognized. Today, all countries with high Internet penetration rate have established high-profile archiving initiatives to crawl and archive the fast-disappearing web content for long-term use. As web technologies evolve, established web archiving techniques face challenges. This paper focuses on the potential impact of the relaxed consistency web design on crawler driven web archiving. Relaxed consistent websites may disseminate, albeit ephemerally, inaccurate and even contradictory information. If captured and preserved in the web archives as historical records, such information will degrade the overall archival quality. To assess the extent of such quality degradation, we build a simplified feed-following application and simulate its operation with synthetic workloads. The results indicate that a non-trivial portion of a relaxed consistency web archive may contain observable inconsistency, and the inconsistency window may extend significantly longer than that observed at the data store. We discuss the nature of such quality degradation and propose a few possible remedies.Comment: 10 pages, 6 figures, CIKM 201

    Tree Projections and Constraint Optimization Problems: Fixed-Parameter Tractability and Parallel Algorithms

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    Tree projections provide a unifying framework to deal with most structural decomposition methods of constraint satisfaction problems (CSPs). Within this framework, a CSP instance is decomposed into a number of sub-problems, called views, whose solutions are either already available or can be computed efficiently. The goal is to arrange portions of these views in a tree-like structure, called tree projection, which determines an efficiently solvable CSP instance equivalent to the original one. Deciding whether a tree projection exists is NP-hard. Solution methods have therefore been proposed in the literature that do not require a tree projection to be given, and that either correctly decide whether the given CSP instance is satisfiable, or return that a tree projection actually does not exist. These approaches had not been generalized so far on CSP extensions for optimization problems, where the goal is to compute a solution of maximum value/minimum cost. The paper fills the gap, by exhibiting a fixed-parameter polynomial-time algorithm that either disproves the existence of tree projections or computes an optimal solution, with the parameter being the size of the expression of the objective function to be optimized over all possible solutions (and not the size of the whole constraint formula, used in related works). Tractability results are also established for the problem of returning the best K solutions. Finally, parallel algorithms for such optimization problems are proposed and analyzed. Given that the classes of acyclic hypergraphs, hypergraphs of bounded treewidth, and hypergraphs of bounded generalized hypertree width are all covered as special cases of the tree projection framework, the results in this paper directly apply to these classes. These classes are extensively considered in the CSP setting, as well as in conjunctive database query evaluation and optimization

    HaIRST: Harvesting Institutional Resources in Scotland Testbed. Final Project Report

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    The HaIRST project conducted research into the design, implementation and deployment of a pilot service for UK-wide access of autonomously created institutional resources in Scotland, the aim being to investigate and advise on some of the technical, cultural, and organisational requirements associated with the deposit, disclosure, and discovery of institutional resources in the JISC Information Environment. The project involved a consortium of Scottish higher and further education institutions, with significant assistance from the Scottish Library and Information Council. The project investigated the use of technologies based on the Open Archives Initiative (OAI), including the implementation of OAI-compatible repositories for metadata which describe and link to institutional digital resources, the use of the OAI protocol for metadata harvesting (OAI-PMH) to automatically copy the metadata from multiple repositories to a central repository, and the creation of a service to search and identify resources described in the central repository. An important aim of the project was to identify issues of metadata interoperability arising from the requirements of individual institutional repositories and their impact on services based on the aggregation of metadata through harvesting. The project also sought to investigate issues in using these technologies for a wide range of resources including learning, teaching and administrative materials as well as the research and scholarly communication materials considered by many of the other projects in the JISC Focus on Access to Institutional Resources (FAIR) Programme, of which HaIRST was a part. The project tested and implemented a number of open source software packages supporting OAI, and was successful in creating a pilot service which provides effective information retrieval of a range of resources created by the project consortium institutions. The pilot service has been extended to cover research and scholarly communication materials produced by other Scottish universities, and administrative materials produced by a non-educational institution in Scotland. It is an effective testbed for further research and development in these areas. The project has worked extensively with a new OAI standard for 'static repositories' which offers a low-barrier, low-cost mechanism for participation in OAI-based consortia by smaller institutions with a low volume of resources. The project identified and successfully tested tools for transforming pre-existing metadata into a format compliant with OAI standards. The project identified and assessed OAI-related documentation in English from around the world, and has produced metadata for retrieving and accessing it. The project created a Web-based advisory service for institutions and consortia. The OAI Scotland Information Service (OAISIS) provides links to related standards, guidance and documentation, and discusses the findings of HaIRST relating to interoperability and the pilot harvesting service. The project found that open source packages relating to OAI can be installed and made to interoperate to create a viable method of sharing institutional resources within a consortium. HaIRST identified issues affecting the interoperability of shared metadata and suggested ways of resolving them to improve the effectiveness and efficiency of shared information retrieval environments based on OAI. The project demonstrated that application of OAI technologies to administrative materials is an effective way for institutions to meet obligations under Freedom of Information legislation

    Open public sector information: from principles to practice

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    Accessible information is the lifeblood of a robust democracy and a productive economy. As part of a worldwide movement, the Australian Government is fundamentally changing the way that information is valued, managed, used and shared with others. The concept that best captures this trend, both in Australia and internationally, is the term \u27public sector information\u27 (PSI). This describes data, information or content that is generated, collected, or funded by or for the government or public institutions. PSI is a valuable resource that underpins all the essential public functions that government discharges. It can be an equally valuable resource outside government. People and business can use PSI to evaluate, respond, research, plan, discover, invent, innovate and aspire. The true value of information is realised only when others can use and build upon it to create new ideas, inventions and strategies. Open PSI is the necessary policy setting to make that happen. It requires, in essence, that government information and data is managed in a way that makes it readily discoverable, accessible and reusable by business and the community. This report details the results of a survey conducted by the Office of the Australian Information Commissioner (OAIC) on how 191 Australian Government agencies manage PSI. The survey was structured around the eight Principles on open public sector information (Open PSI principles) that were published by the OAIC in 2011. The key finding of this report is that Australian Government agencies are actively embracing an open access and proactive disclosure culture. The high response rate to this survey confirms that finding. The widespread and growing use of digital and web technologies to support a PSI transformation is another sign. There are nevertheless many policy challenges and practical obstacles that must be tackled. It is more a time of transition than fulfilment. This transition – or cultural shift – is more successful when built on four elements: agency leadership, officer innovation, community engagement and investment in information infrastructure. Those four elements were identified by agencies themselves as key issues in developing national information policy. Shortcomings in existing policies, structure and information management practices are highlighted by the survey responses: Transitioning to open access and proactive publication requires cultural change, including more active sponsorship of this philosophy by agency leaders; this is particularly important to overcome resistance or disengagement within agencies. Existing systems for record keeping, information governance, information release and user consultation are not suitably designed for the new era of open PSI, in which government information and data must be valued as a core agency asset and a national resource. Information management systems do not always apply uniformly across agencies; from an open PSI perspective there can be indefensible differences in information management practices across agency branches and locations. A great deal of valuable information is held by agencies in legacy documents that must be reformatted for digital publication; this can be a costly and technologically challenging process. Not all agencies have the technical specialisation and capacity to implement open PSI, on issues such as attachment of metadata, conformance to WCAG 2.0 and data release in an open and standards-based format. The default position of open access licensing is not clearly or robustly stated, nor properly reflected in the practice of government agencies. Agencies have been successful in identifying information that is required to be published under the Information Publication Scheme, but have not been as successful in identifying or prioritising other information that can be published through the agency website or on open data portals. Budgetary limitations hamper the capacity of agencies to be more dynamic in implementing an open PSI culture. An open PSI access strategy is vital to enable Australia to fully enjoy the economic, regulatory and cultural benefits of an open government model. Great strides to unlock PSI assets have recently been taken through the combined impact of the Government\u27s Gov 2.0 strategy, freedom of information changes, the innovation agenda, a shift in public service culture, and service delivery reform

    On the design of a multiagent user interface for Next Generation Geographic Information System

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    In this thesis, a multiagent user interface architecture is designed for the Next Generation Geographic Information System(NGGIS) which supports the following advanced features: multiple users, multiple views, direct manipulation, distribution, and intelligence. In this architecture, agent is a basic functional unit. Agents cooperate with each other by exchanging messages. The User is just a special agent who communicates with any other agents. The ShowCase and its cooperative agents are specialized to present the geographic objects in different views. The WorkShop and its cooperative agents provide a complete interface to allow the user to manipulate the GIS objects directly. The Monitor is specialized to enforce the semantic constrains and control the system consistency. The Interaction Expert interprets multimedia user input and generates multimedia output by driving other agents. The Selector is a cooperative agent of both WorkShop and ShowCase which allows users to select geographic objects with specific constraints

    Interactive visual exploration of a large spatio-temporal dataset: Reflections on a geovisualization mashup

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    Exploratory visual analysis is useful for the preliminary investigation of large structured, multifaceted spatio-temporal datasets. This process requires the selection and aggregation of records by time, space and attribute, the ability to transform data and the flexibility to apply appropriate visual encodings and interactions. We propose an approach inspired by geographical 'mashups' in which freely-available functionality and data are loosely but flexibly combined using de facto exchange standards. Our case study combines MySQL, PHP and the LandSerf GIS to allow Google Earth to be used for visual synthesis and interaction with encodings described in KML. This approach is applied to the exploration of a log of 1.42 million requests made of a mobile directory service. Novel combinations of interaction and visual encoding are developed including spatial 'tag clouds', 'tag maps', 'data dials' and multi-scale density surfaces. Four aspects of the approach are informally evaluated: the visual encodings employed, their success in the visual exploration of the clataset, the specific tools used and the 'rnashup' approach. Preliminary findings will be beneficial to others considering using mashups for visualization. The specific techniques developed may be more widely applied to offer insights into the structure of multifarious spatio-temporal data of the type explored here

    State-of-the-art on evolution and reactivity

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    This report starts by, in Chapter 1, outlining aspects of querying and updating resources on the Web and on the Semantic Web, including the development of query and update languages to be carried out within the Rewerse project. From this outline, it becomes clear that several existing research areas and topics are of interest for this work in Rewerse. In the remainder of this report we further present state of the art surveys in a selection of such areas and topics. More precisely: in Chapter 2 we give an overview of logics for reasoning about state change and updates; Chapter 3 is devoted to briefly describing existing update languages for the Web, and also for updating logic programs; in Chapter 4 event-condition-action rules, both in the context of active database systems and in the context of semistructured data, are surveyed; in Chapter 5 we give an overview of some relevant rule-based agents frameworks
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