59,451 research outputs found

    Designing role-based view for object-relational databases

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    In a federated database system, a view mechanism is crucial since it is used to define exportable subsets of data ; to perform a virtual restructuring d ataset; and to construct the integrated schema. The view service in federated databa se systems must be capable of retaining as much semantic information as possible. The object-oriented ( 0 - 0 ) model was considered the suitable canonical data model since it meets the original criteria for canonical model selection. However, with the emergence of stronger object-relational (0 -R ) model, the re is a clear argument for using an 0 - R canonical model in the federation. Hence, research should now focus on th e development of semantically powerful view mechanism for th e newer model. Meanwhile, the availability of real 0 -R technologies offers researchers the opportunity to develop different forms of view mechanisms. The concept of roles has been widely studied in 0 - 0 modelling and development. The role model represents some characteristics that the traditional 0-0 model lacked, such as object migration, multiple occurrences and context-dependent access. While many forms of 0-0 views were designed for the 0-0 canonical model, one option was to extend the 0-0 model to incorporate a role model. In a role model, the real entity is modelled in the form of a role rather than an object. An object represents the permanent properties of an entity is a root object; and an object represents the temporary properties of an entity is a role object. The contribution of this research is to design a view system that employees the concept of roles for the 0 -R canonical model in a federated database system. In this thesis, an examination of the current 0 -R metamodel is provided first in order to provide an environment for recognising the roleview metadata and measuring the view performance; then a Roleview Definition Language (RDL) is introduced, along with the semantics for defining virtual classes and generating virtua l extents; finally, a working prototype is provided to prove th e role-based view system is implementable and the syntax is semantically correct

    Further results on independent Metropolis-Hastings-Klein sampling

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    Sampling from a lattice Gaussian distribution is emerging as an important problem in coding and cryptography. This paper gives a further analysis of the independent Metropolis-Hastings-Klein (MHK) algorithm we presented at ISIT 2015. We derive the exact spectral gap of the induced Markov chain, which dictates the convergence rate of the independent MHK algorithm. Then, we apply the independent MHK algorithm to lattice decoding and obtained the decoding complexity for solving the CVP as Õ(e∥Bx-c∥2 / mini ∥b̂i∥2). Finally, the tradeoff between decoding radius and complexity is also established