Ángeles S. Places

Word-based self-indexes for natural language text

The inverted index supports efficient full-text searches on natural language text collections. It requires some extra space over the compressed text that can be traded for search speed. It is usually fast for single-word searches, yet phrase searches require more expensive intersections. In this article we introduce a different kind of index. It replaces the text using essentially the same space required by the compressed text alone (compression ratio around 35%). Within this space it supports not only decompression of arbitrary passages, but efficient word and phrase searches. Searches are orders of magnitude faster than those over inverted indexes when looking for phrases, and still faster on single-word searches when little space is available. Our new indexes are particularly fast at counting the occurrences of words or phrases. This is useful for computing relevance of words or phrases. We adapt self-indexes that succeeded in indexing arbitrary strings within compressed space to deal with large alphabets. Natural language texts are then regarded as sequences of words, not characters, to achieve word-based self-indexes. We design an architecture that separates the searchable sequence from its presentation aspects. This permits applying case folding, stemming, removing stopwords, etc. as is usual on inverted indexes.

Optimal Pivots to Minimize the Index Size for Metric Access Methods

We consider the problem of similarity search in metric spaces with costly distance functions and large databases. There is a trade-off between the amount of information stored in the index and the reduction in the number of comparisons for solving a query. Pivot-based methods clearly outperform clustering-based ones in number of comparisons, but their space requirements are higher and this can prevent their application in real problems. Therefore, several strategies have been proposed that reduce the space needed by pivot-based methods, as BAESA, FQA or KVP. In this paper, we analyze the usefulness of pivots depending on their proximity to the object. As consequence of this analysis, we propose a new pivot-based method that requires an amount of space equal or very close to that needed by clustering-based methods. We provide experimental results that show that our proposal represents a competitive strategy to clustering oriented solutions when using the same amount of memory.

Self-indexing Natural Language

Self-indexing is a concept developed for indexing arbitrary strings. It has been enormously successful to reduce the size of the large indexes typically used on strings, namely suffix trees and arrays. Self-indexes represent a string in a space close to its compressed size and provide indexed searching on it. On natural language, a compressed inverted index over the compressed text already provides a reasonable alternative, in space and time, for indexed searching of words and phrases. In this paper we explore the possibility of regarding natural language text as a string of words and applying a self-index to it. There are several challenges involved, such as dealing with a very large alphabet and detaching searchable content from non-searchable presentation aspects in the text. As a result, we show that the self-index requires space very close to that of the best word-based compressors, and that it obtains better search time than inverted indexes (using the same overall space) when searching for phrases.

The Galician virtual library

Purpose – This study aims to present the digital library Galician virtual library (BVG, for “Biblioteca Virtual Galega”) in Galician.Design/methodology/approach – The paper shows the objectives pursued by the BVG, its development, putting special emphasis on the main technological challenges, and presents some data about its usage.Findings – A digital library can be used to stimulate a lesser‐used language and to promote the culture and tourism of a region.Originality/value – The paper shows how a digital library can be used to strengthen the Galician language, which is currently categorised as a “Lesser Used Language” in the European Community and to contribute to the preservation and spreading of Galician culture and literary works, either from current authors or from previous documents. It also provides a digital publishing house for new authors and opens a communication channel between current authors and their readers. Finally, it helps to connect a scattered community like the Galician, offering a c...

A case study on business process recovery using an e-government system

Business processes have become one of the key assets of organization, since these processes allow them to discover and control what occurs in their environments, with information systems automating most of an organizations processes. Unfortunately, and as a result of uncontrolled maintenance, information systems age over time until it is necessary to replace them with new and modernized systems. However, while systems are aging, meaningful business knowledge that is not present in any of the organizations other assets gradually becomes embedded in them. The preservation of this knowledge through the recovery of the underlying business processes is, therefore, a critical problem. This paper provides, as a solution to the aforementioned problem, a model‐driven procedure for recovering business processes from legacy information systems. The procedure proposes a set of models at different abstraction levels, along with the model transformations between them. The paper also provides a supporting tool, which facilitates its adoption. Moreover, a real‐life case study concerning an e‐government system applies the proposed recovery procedure to validate its effectiveness and efficiency. The case study was carried out by following a formal protocol to improve its rigor and replicability. Copyright

An empirical comparison of static and dynamic business process mining

Legacy information systems age over time as a consequence of the uncontrolled maintenance and need to be modernized. Process mining allows the discovery of business processes embedded in legacy information systems, which is necessary to preserve the legacy business knowledge, and align them with the new, modernized information systems. There are two main approaches to address the mining of business processes from legacy information systems: (i) the static approach that only considers legacy source codes elements from a syntactical viewpoint; and (ii) the dynamic approach, which also considers information derived by system execution. Unfortunately, there is a lack of empirical evidence facilitating the selection of one of them. This paper provides a formal comparison of the static and dynamic approach through a case study. This study shows that the static approach provides better performance, while the dynamic approach discovers more accurate business processes.

Using geographical information systems to browse touristic information.

The current expansion of Internet makes it one of the most popular places to publish and search for almost any kind of information. In particular, touristic information, not only about tours or information about resources, places, museums or monuments, but also cultural tourism, has gained much attention in the last years. We propose the use of geographical information systems technology (GIS) that provides interfaces capable of displaying interactive maps with information associated to the elements present in such maps. In this paper, we present a Web interface to access touristic information about Galicia (Spain) using GIS technology to easily find any touristic or cultural information. This interface is enclosed in the Galician Virtual Library (http://bvg.udc.es) Web site.

A documental database query language

This work presents a natural language based technique to build user interfaces to query document databases through the web. We call such technique Bounded Natural Language (BNL). Interfaces based on BNL are useful to query document databases containing only structured data, containing only text or containing both of them. That is, the underlying formalism of BNL can integrate restrictions over structured and non-structured data (as text).Interfaces using BNL can be programmed ad hoc for any document database but in this paper we present a system with an ontology based architecture in which the user interface is automatically generated by a software module (User Interface Generator) capable of reading and following the ontology. This ontology is a conceptualization of the database model, which uses a label in natural language for any concept in the ontology. Each label represents the usual name for a concept in the real world.The ontology includes general concepts useful when the user is interested in documents in any corpus in the database, and specific concepts useful when the user is interested in a specific corpus. That is, databases can store one or more corpus of documents and queries can be issued either over the whole database or over a specific corpus.The ontology guides the execution of the User Interface Generator and other software modules in such a way that any change in the database does not imply making changes in the program code, because the whole system runs following the ontology. That is, if a modification in the database schema occurs, only the ontology must be changed and the User Interface Generator will produce a new and different user interface adapted to the new database.

Rank and Select for Succinct Data Structures

In this paper, we study different approaches for rank and select on sequences of bytes and propose new implementation strategies. Extensive experimental evaluation comparing the efficiency of the different alternatives are provided. Given a sequence of bits, a rank query counts the number of occurrences of the bit 1 up to a given position, and a select query returns the position of the ith occurrence of the bit 1. These operations are widely used in information retrieval and management, being the base of several data structures and algorithms for text collections, graphs, etc. There exist solutions for computing these operations on sequences of bits in constant time using additional information. However, new applications require rank and select to be computed on sequences of bytes instead of bits. The solutions for the binary case are not directly applicable to sequences of bytes. The existing solutions for the byte case vary in their space-time trade-off which can still be improved.

Retrieving Documents with Geographic References Using a Spatial Index Structure Based on Ontologies

Both Geographic Information Systemsand Information Retrievalhave been very active research fields in the last decades. Lately, a new research field called Geographic Information Retrievalhas appeared from the intersection of these two fields. The main goal of this field is to define index structures and techniques to efficiently store and retrieve documents using both the text and the geographic references contained within the text. We present in this paper a new index structure that combines an inverted index, a spatial index, and an ontology-based structure. This structure improves the query capabilities of other proposals. In addition, we describe the architecture of a system for geographic information retrieval that uses this new index structure. This architecture defines a workflow for the extraction of the geographic references in the document.