26,277 research outputs found
On the Selection of Optimal Index Configuration in OO Databases
An operation in object-oriented databases gives rise to the processing of a path. Several database operations may result into the same path. The authors address the problem of optimal index configuration for a single path. As it is shown an optimal index configuration for a path can be achieved by splitting the path into subpaths and by indexing each subpath with the optimal index organization. The authors present an algorithm which is able to select an optimal index configuration for a given path. The authors consider a limited number of existing indexing techniques (simple index, inherited index, nested inherited index, multi-index, and multi-inherited index) but the principles of the algorithm remain the same adding more indexing technique
New Methods, Current Trends and Software Infrastructure for NLP
The increasing use of `new methods' in NLP, which the NeMLaP conference
series exemplifies, occurs in the context of a wider shift in the nature and
concerns of the discipline. This paper begins with a short review of this
context and significant trends in the field. The review motivates and leads to
a set of requirements for support software of general utility for NLP research
and development workers. A freely-available system designed to meet these
requirements is described (called GATE - a General Architecture for Text
Engineering). Information Extraction (IE), in the sense defined by the Message
Understanding Conferences (ARPA \cite{Arp95}), is an NLP application in which
many of the new methods have found a home (Hobbs \cite{Hob93}; Jacobs ed.
\cite{Jac92}). An IE system based on GATE is also available for research
purposes, and this is described. Lastly we review related work.Comment: 12 pages, LaTeX, uses nemlap.sty (included
A Taxonomy of Data Grids for Distributed Data Sharing, Management and Processing
Data Grids have been adopted as the platform for scientific communities that
need to share, access, transport, process and manage large data collections
distributed worldwide. They combine high-end computing technologies with
high-performance networking and wide-area storage management techniques. In
this paper, we discuss the key concepts behind Data Grids and compare them with
other data sharing and distribution paradigms such as content delivery
networks, peer-to-peer networks and distributed databases. We then provide
comprehensive taxonomies that cover various aspects of architecture, data
transportation, data replication and resource allocation and scheduling.
Finally, we map the proposed taxonomy to various Data Grid systems not only to
validate the taxonomy but also to identify areas for future exploration.
Through this taxonomy, we aim to categorise existing systems to better
understand their goals and their methodology. This would help evaluate their
applicability for solving similar problems. This taxonomy also provides a "gap
analysis" of this area through which researchers can potentially identify new
issues for investigation. Finally, we hope that the proposed taxonomy and
mapping also helps to provide an easy way for new practitioners to understand
this complex area of research.Comment: 46 pages, 16 figures, Technical Repor
On the Complexity of Nonrecursive XQuery and Functional Query Languages on Complex Values
This paper studies the complexity of evaluating functional query languages
for complex values such as monad algebra and the recursion-free fragment of
XQuery.
We show that monad algebra with equality restricted to atomic values is
complete for the class TA[2^{O(n)}, O(n)] of problems solvable in linear
exponential time with a linear number of alternations. The monotone fragment of
monad algebra with atomic value equality but without negation is complete for
nondeterministic exponential time. For monad algebra with deep equality, we
establish TA[2^{O(n)}, O(n)] lower and exponential-space upper bounds.
Then we study a fragment of XQuery, Core XQuery, that seems to incorporate
all the features of a query language on complex values that are traditionally
deemed essential. A close connection between monad algebra on lists and Core
XQuery (with ``child'' as the only axis) is exhibited, and it is shown that
these languages are expressively equivalent up to representation issues. We
show that Core XQuery is just as hard as monad algebra w.r.t. combined
complexity, and that it is in TC0 if the query is assumed fixed.Comment: Long version of PODS 2005 pape
- …