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91.
We describe a suite of standards, resources and tools for computational encoding and processing of Modern Hebrew texts. These
include an array of XML schemas for representing linguistic resources; a variety of text corpora, raw, automatically processed
and manually annotated; lexical databases, including a broad-coverage monolingual lexicon, a bilingual dictionary and a WordNet;
and morphological processors which can analyze, generate and disambiguate Hebrew word forms. The resources are developed under
centralized supervision, so that they are compatible with each other. They are freely available and many of them have already
been used for several applications, both academic and industrial.
相似文献
Shuly WintnerEmail: |
92.
Data integration with uncertainty 总被引:1,自引:0,他引:1
Xin Luna Dong Alon Halevy Cong Yu 《The VLDB Journal The International Journal on Very Large Data Bases》2009,18(2):469-500
This paper reports our first set of results on managing uncertainty in data integration. We posit that data-integration systems
need to handle uncertainty at three levels and do so in a principled fashion. First, the semantic mappings between the data
sources and the mediated schema may be approximate because there may be too many of them to be created and maintained or because
in some domains (e.g., bioinformatics) it is not clear what the mappings should be. Second, the data from the sources may
be extracted using information extraction techniques and so may yield erroneous data. Third, queries to the system may be
posed with keywords rather than in a structured form. As a first step to building such a system, we introduce the concept
of probabilistic schema mappings and analyze their formal foundations. We show that there are two possible semantics for such
mappings: by-table semantics assumes that there exists a correct mapping but we do not know what it is; by-tuple semantics assumes that the correct mapping may depend on the particular tuple in the source data. We present the query complexity
and algorithms for answering queries in the presence of probabilistic schema mappings, and we describe an algorithm for efficiently
computing the top-k answers to queries in such a setting. Finally, we consider using probabilistic mappings in the scenario of data exchange. 相似文献
93.
Representing uncertain data: models, properties, and algorithms 总被引:1,自引:0,他引:1
Anish Das Sarma Omar Benjelloun Alon Halevy Shubha Nabar Jennifer Widom 《The VLDB Journal The International Journal on Very Large Data Bases》2009,18(5):989-1019
In general terms, an uncertain relation encodes a set of possible certain relations. There are many ways to represent uncertainty,
ranging from alternative values for attributes to rich constraint languages. Among the possible models for uncertain data,
there is a tension between simple and intuitive models, which tend to be incomplete, and complete models, which tend to be nonintuitive and more complex than necessary for many applications. We present a space
of models for representing uncertain data based on a variety of uncertainty constructs and tuple-existence constraints. We
explore a number of properties and results for these models. We study completeness of the models, as well as closure under
relational operations, and we give results relating closure and completeness. We then examine whether different models guarantee
unique representations of uncertain data, and for those models that do not, we provide complexity results and algorithms for
testing equivalence of representations. The next problem we consider is that of minimizing the size of representation of models,
showing that minimizing the number of tuples also minimizes the size of constraints. We show that minimization is intractable
in general and study the more restricted problem of maintaining minimality incrementally when performing operations. Finally,
we present several results on the problem of approximating uncertain data in an insufficiently expressive model. 相似文献
94.
MiniCon: A scalable algorithm for answering queries using views 总被引:5,自引:0,他引:5
Rachel Pottinger Alon Halevy 《The VLDB Journal The International Journal on Very Large Data Bases》2001,10(2-3):182-198
The problem of answering queries using views is to find efficient methods of answering a query using a set of previously
materialized views over the database, rather than accessing the database relations. The problem has received significant attention
because of its relevance to a wide variety of data management problems, such as data integration, query optimization, and
the maintenance of physical data independence. To date, the performance of proposed algorithms has received very little attention,
and in particular, their scale up in the presence of a large number of views is unknown. We first analyze two previous algorithms,
the bucket algorithm and the inverse-rules, and show their deficiencies. We then describe the MiniCon, a novel algorithm for
finding the maximally-contained rewriting of a conjunctive query using a set of conjunctive views. We present the first experimental
study of algorithms for answering queries using views. The study shows that the MiniCon scales up well and significantly outperforms
the previous algorithms. We describe an extension of the MiniCon to handle comparison predicates, and show its performance
experimentally. Finally, we describe how the MiniCon can be extended to the context of query optimization.
Received: 15 October 2000 / Accepted: 15 April 2001 Published online: 28 June 2001 相似文献
95.
Morphologically rich languages pose a challenge for statistical machine translation (SMT). This challenge is magnified when translating into a morphologically rich language. In this work we address this challenge in the framework of a broad-coverage English-to-Arabic phrase based statistical machine translation (PBSMT). We explore the largest-to-date set of Arabic segmentation schemes ranging from full word form to fully segmented forms and examine the effects on system performance. Our results show a difference of 2.31 BLEU points averaged over all test sets between the best and worst segmentation schemes indicating that the choice of the segmentation scheme has a significant effect on the performance of an English-to-Arabic PBSMT system in a large data scenario. We show that a simple segmentation scheme can perform as well as the best and more complicated segmentation scheme. An in-depth analysis on the effect of segmentation choices on the components of a PBSMT system reveals that text fragmentation has a negative effect on the perplexity of the language models and that aggressive segmentation can significantly increase the size of the phrase table and the uncertainty in choosing the candidate translation phrases during decoding. An investigation conducted on the output of the different systems, reveals the complementary nature of the output and the great potential in combining them. 相似文献
96.
This work presents a simple method to obtain effects similar to those obtained by real mechanical loading and real inertia variation but without any mechanical parts supplementary to the electric motor of the studied electric drive. The electric motor itself produces the load torque and the inertia variation using digital signal processing software. Therefore, the electric drive is virtually torque and inertia loaded, while its behavior is similar to that of the actual loaded drive. The present method could be used to test the implementation of control algorithms or for didactic purposes using motion control kits found on the market. The present method is used with laboratory works of the DSP Fundamentals in power electronics course at the Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel. 相似文献
97.
98.
Matan Cafri Alon Malka Helen Dilman Moshe P. Dariel Nahum Frage 《International Journal of Applied Ceramic Technology》2014,11(2):273-279
Reaction‐bonded boron carbide was manufactured by infiltrating porous boron carbide preforms at 1273 K with a Mg‐Si eutectic alloy. The resulting composite material consists, in addition to the original B4C, of SiC, Mg2Si, and a Mg‐rich complex boride/carbide Mgx(Al,Si)y(B,C)z phase. The composites display high hardness (1700 HV), Young's modulus (356 MPa) and a moderate bending strength (230 MPa). The ballistic efficiency (of about 6.7), as determined by the depth of penetration method, is much higher than that of alumina and similar to that of silicon‐infiltrated reaction‐bonded composites. 相似文献
99.
The Unreasonable Effectiveness of Data 总被引:2,自引:0,他引:2
Problems that involve interacting with humans, such as natural language understanding, have not proven to be solvable by concise, neat formulas like F = ma. Instead, the best approach appears to be to embrace the complexity of the domain and address it by harnessing the power of data: if other humans engage in the tasks and generate large amounts of unlabeled, noisy data, new algorithms can be used to build high-quality models from the data. 相似文献
100.
Ludwig A Leviatan Y 《Journal of the Optical Society of America. A, Optics, image science, and vision》2003,20(8):1553-1562
We introduce a solution based on the source-model technique for periodic structures for the problem of electromagnetic scattering by a two-dimensional photonic bandgap crystal slab illuminated by a transverse-magnetic plane wave. The proposed technique takes advantage of the periodicity of the slab by solving the problem within the unit cell of the periodic structure. The results imply the existence of a frequency bandgap and provide a valuable insight into the relationship between the dimensions of a finite periodic structure and its frequency bandgap characteristics. A comparison shows a discrepancy between the frequency bandgap obtained for a very thick slab and the bandgap obtained by solving the corresponding two-dimensionally infinite periodic structure. The final part of the paper is devoted to explaining in detail this apparent discrepancy. 相似文献