841 research outputs found
A model for querying semistructured data through the exploitation of regular sub-structures
Much research has been undertaken in order to speed up the processing of semistructured data in general and XML in particular. Many approaches for storage, compression, indexing and querying exist, e.g. [1, 2]. We do not present yet another such algorithm but a unifying model in which these algorithm can be understood. The key idea behind this research is the assumption, that most practical queries are based on a particular pattern of data that can be deduced from the query and which can then be captured using a regular structure amendable to efficient processing techniques
Generating admissible space-time meshes for moving domains in -dimensions
In this paper we present a discontinuous Galerkin finite element method for
the solution of the transient Stokes equations on moving domains. For the
discretization we use an interior penalty Galerkin approach in space, and an
upwind technique in time. The method is based on a decomposition of the
space-time cylinder into finite elements. Our focus lies on three-dimensional
moving geometries, thus we need to triangulate four dimensional objects. For
this we will present an algorithm to generate -dimensional simplex
space-time meshes and we show under natural assumptions that the resulting
space-time meshes are admissible. Further we will show how one can generate a
four-dimensional object resolving the domain movement. First numerical results
for the transient Stokes equations on triangulations generated with the newly
developed meshing algorithm are presented
Compact in-memory representation of XML data : design and implementation of a compressed DOM for data-centric documents
Over recent years XML has evolved from a document exchange format to a multi-purpose data storage and retrieval solution. To make use of the full potential of XML in the domain of large, data-centric documents it is necessary to have easy and fast access to individual data elements. We describe an implementation of the Document Object Model (DOM) that is designed with these objectives in mind. It uses compression to allow large documents to be stored in the computer's main memory. Query-relevant DOM methods are optimised to work on top of the created data structure. Measurements indicate that compression up to a factor of 5 is possible without losing the ability to directly address individual elements. No prior decompression is needed to query and locate nodes
TypEx : a type based approach to XML stream querying
We consider the topic of query evaluation over semistructured information streams, and XML data streams in particular. Streaming evaluation methods are necessarily eventdriven, which is in tension with high-level query models; in general, the more expressive the query language, the harder it is to translate queries into an event-based implementation with finite resource bounds
A positive lower bound for
Nearly 60 years ago, Erd\H{o}s and Szekeres raised the question of whether
for all irrationals . Despite its simple formulation, the question has
remained unanswered. It was shown by Lubinsky in 1999 that the answer is yes if
has unbounded continued fraction coefficients, and it was suggested
that the answer is yes in general. However, we show in this paper that for the
golden ratio ,
providing a negative answer to this long-standing open problem
The auxiliary space preconditioner for the de Rham complex
We generalize the construction and analysis of auxiliary space
preconditioners to the n-dimensional finite element subcomplex of the de Rham
complex. These preconditioners are based on a generalization of a decomposition
of Sobolev space functions into a regular part and a potential. A discrete
version is easily established using the tools of finite element exterior
calculus. We then discuss the four-dimensional de Rham complex in detail. By
identifying forms in four dimensions (4D) with simple proxies, form operations
are written out in terms of familiar algebraic operations on matrices, vectors,
and scalars. This provides the basis for our implementation of the
preconditioners in 4D. Extensive numerical experiments illustrate their
performance, practical scalability, and parameter robustness, all in accordance
with the theory
Space-Time Isogeometric Analysis of Parabolic Evolution Equations
We present and analyze a new stable space-time Isogeometric Analysis (IgA)
method for the numerical solution of parabolic evolution equations in fixed and
moving spatial computational domains. The discrete bilinear form is elliptic on
the IgA space with respect to a discrete energy norm. This property together
with a corresponding boundedness property, consistency and approximation
results for the IgA spaces yields an a priori discretization error estimate
with respect to the discrete norm. The theoretical results are confirmed by
several numerical experiments with low- and high-order IgA spaces
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