2,397 research outputs found
A stemming algorithm for Latvian
The thesis covers construction, application and evaluation of a stemming algorithm for
advanced information searching and retrieval in Latvian databases. Its aim is to examine
the following two questions:
Is it possible to apply for Latvian a suffix removal algorithm originally designed
for English?
Can stemming in Latvian produce the same or better information retrieval results
than manual truncation?
In order to achieve these aims, the role and importance of automatic word conflation
both for document indexing and information retrieval are characterised. A review of
literature, which analyzes and evaluates different types of stemming techniques and
retrospective development of stemming algorithms, justifies the necessity to apply this
advanced IR method also for Latvian. Comparative analysis of morphological structure
both for English and Latvian language determined the selection of Porter's suffix
removal algorithm as a basis for the Latvian sternmer.
An extensive list of Latvian stopwords including conjunctions, particles and adverbs,
was designed and added to the initial sternmer in order to eliminate insignificant words
from further processing. A number of specific modifications and changes related to the
Latvian language were carried out to the structure and rules of the original stemming
algorithm.
Analysis of word stemming based on Latvian electronic dictionary and Latvian text
fragments confirmed that the suffix removal technique can be successfully applied also
to Latvian language. An evaluation study of user search statements revealed that the
stemming algorithm to a certain extent can improve effectiveness of information
retrieval
The Role of Term Symmetry in E-Unification and E-Completion
A major portion of the work and time involved in completing an incomplete set of reductions using an E-completion procedure such as the one described by Knuth and Bendix [070] or its extension to associative-commutative equational theories as described by Peterson and Stickel [PS81] is spent calculating critical pairs and subsequently testing them for coherence. A pruning technique which removes from consideration those critical pairs that represent redundant or superfluous information, either before, during, or after their calculation, can therefore make a marked difference in the run time and efficiency of an E-completion procedure to which it is applied.
The exploitation of term symmetry is one such pruning technique. The calculation of redundant critical pairs can be avoided by detecting the term symmetries that can occur between the subterms of the left-hand side of the major reduction being used, and later between the unifiers of these subterms with the left-hand side of the minor reduction. After calculation, and even after reduction to normal form, the observation of term symmetries can lead to significant savings.
The results in this paper were achieved through the development and use of a flexible E-unification algorithm which is currently written to process pairs of terms which may contain any combination of Null-E, C (Commutative), AC (Associative-Commutative) and ACI (Associative-Commutative with Identity) operators. One characteristic of this E-unification algorithm that we have not observed in any other to date is the ability to process a pair of terms which have different ACI top-level operators. In addition, the algorithm is a modular design which is a variation of the Yelick model [Ye85], and is easily extended to process terms containing operators of additional equational theories by simply plugging in a unification module for the new theory
Quantitative Comparison of Abundance Structures of Generalized Communities: From B-Cell Receptor Repertoires to Microbiomes
The \emph{community}, the assemblage of organisms co-existing in a given
space and time, has the potential to become one of the unifying concepts of
biology, especially with the advent of high-throughput sequencing experiments
that reveal genetic diversity exhaustively. In this spirit we show that a tool
from community ecology, the Rank Abundance Distribution (RAD), can be turned by
the new MaxRank normalization method into a generic, expressive descriptor for
quantitative comparison of communities in many areas of biology. To illustrate
the versatility of the method, we analyze RADs from various \emph{generalized
communities}, i.e.\ assemblages of genetically diverse cells or organisms,
including human B cells, gut microbiomes under antibiotic treatment and of
different ages and countries of origin, and other human and environmental
microbial communities. We show that normalized RADs enable novel quantitative
approaches that help to understand structures and dynamics of complex
generalize communities
Computational phylogenetics and the classification of South American languages
In recent years, South Americanist linguists have embraced computational phylogenetic methods to resolve the numerous outstanding questions about the genealogi- cal relationships among the languages of the continent. We provide a critical review of the methods and language classification results that have accumulated thus far, emphasizing the superiority of character-based methods over distance-based ones and the importance of develop- ing adequate comparative datasets for producing well- resolved classifications
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