RcppCWB-packge: Rcpp Bindings for the Corpus Workbench (CWB).

Description The Idea Behind RcppCWB Implementation Getting Started with RcppCWB Digging Deeper Acknowledgements Author(s) References Examples

Description

The RcppCWB package is a wrapper library to expose core functions of the Open Corpus Workbench (CWB). This includes the low-level functionality of the Corpus Library (CL) as well as capacities to use the query syntax of the Corpus Query Processor (CQP).

The Idea Behind RcppCWB

The Open Corpus Workbench (CWB) is an indexing and querying engine popular in corpus-assisted research. Its core aim is to support working efficiently with large, structurally and linguistically annotated corpora. First of all, the CWB includes tools to index and compress corpora. Second, the Corpus Library (CL) offers low-level functionality to retrieve information from CWB indexed corpora. Third, the Corpus Query Processor (CQP) offers a syntax that allows to perform anything from simple to complex queries, using different annotation layers of corpora.

The CWB is a classical tool which has inspired a set of developments. A persisting advantage of the CWB is its mature, open source code base that is actively maintained by a community of developers. It is used as a robust and efficient backend for widely used tools such as TXM (http://textometrie.ens-lyon.fr) or CQPweb (http://cwb.sourceforge.net/cqpweb.php). Its uncompromising C implementation guarantees speed and makes it well suited to be integrated with R at the same time.

The package RcppCWB is a follow-up on the rcqp package that has pioneered to expose CWB functionality from within R. Indeed, the rcqp package, published at CRAN in 2015, offers robust access to CWB functionality. However, the "pure C" implementation of the rcqp package creates difficulties to make the package portable to Windows. The primary purpose of the RcppCWB package is to reimplement a wrapper library for the CWB using a design that makes it easier to achieve cross-platform portability.

Even though RcppCWB functions may be used directly, the package is designed to serve as an interface to CWB indexed corpora in packages with higher-level functionality. In this regard, RcppCWB is the backend of the polmineR package. It is deliberately open to be used in other contexts. The package may stimulate using linguistically annotated, indexed and compressed corpora on all platforms. The paradigm of working with text as linguistic data may benefit from RcppCWB.

Implementation

When building the package, the first step is to compile the relevant parts of the CWB on Linux and macOS machines. On Windows, cross-compiled binaries are downloaded from a GitHub repository of the PolMine Project (https://github.com/PolMine/libcl). Second, Rcpp wrappers are compiled and make the relevant functions of the Corpus Library and CQP accessible. In addition to genuine CWB functions, RcppCWB offers a set of higher level functions implemented using Rcpp for common performance critical tasks.

Getting Started with RcppCWB

To understand the data storage model of the CWB, in particular the notions of positional and structural attributes (s- and p-attributes), the vignette of the rcqp package is a very good starting point (see references).

The CWB 'Corpus Encoding Tutorial' explains how to create your own corpus, the 'CQP Query Language Tutorial' introduces the syntax of CQP (see references).

The RcppCWB package includes a sample corpus (REUTERS, the data also included in the tm package). The examples in the documentation of the functions may be a good starting point to understand how to use RcppCWB.

Digging Deeper

The original paper of Christ (1994) explains the design choices of the CWB. The indexing and compression techniques of the CWB (Huffman coding) are explained in Witten et al. (1999).

Acknowledgements

The work of the all developers of the CWB is gratefully acknowledged. There is a particular intellectual debt to Bernard Desgraupes and Sylvain Loiseau, and the rcqp package they developed as the original R wrapper to expose the functionality of the CWB.

Author(s)

Andreas Blaette ([email protected])

References

Christ, O. 1994. "A modular and flexible architecture for an integrated corpus query system", in: Proceedings of COMPLEX '94, pp. 23-32. Budapest. Available online at http://cwb.sourceforge.net/files/Christ1994.pdf

Desgraupes, B.; Loiseau, S. 2012. Introduction to the rcqp package. Vignette of the rcqp package. Available at the CRAN archive at https://cran.r-project.org/src/contrib/Archive/rcqp/

Evert, S. 2005. The CQP Query Language Tutorial. Available online at http://cwb.sourceforge.net/files/CWB_Encoding_Tutorial.pdf

Evert, S. 2005. The IMS Open Corpus Workbench (CWB). Corpus Encoding Tutorial. Available online at http://cwb.sourceforge.net/files/CWB_Encoding_Tutorial.pdf

Open Corpus Workbench (http://cwb.sourceforge.net)

Witten, I.H.; Moffat, A.; Bell, T.C. (1999). Managing Gigabytes. Morgan Kaufmann Publishing, San Francisco, 2nd edition.

Examples

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# functions of the corpus library (starting with cl) expose the low-level
# access to the CWB corpus library (CL)

registry <- if (!check_pkg_registry_files()) use_tmp_registry() else get_pkg_registry()
ids <- cl_cpos2id("REUTERS", cpos = 1:20, p_attribute = "word", registry = registry)
tokens <- cl_id2str("REUTERS", id = ids, p_attribute = "word", registry = registry)
print(paste(tokens, collapse = " "))

# To use the corpus query processor (CQP) and its syntax, it is necessary first
# to initialize CQP (example: get concordances of 'oil')

cqp_initialize(registry)
cqp_query("REUTERS", query = '[]{5} "oil" []{5}')
cpos_matrix <- cqp_dump_subcorpus("REUTERS")
concordances_oil <- apply(
  cpos_matrix, 1,
  function(row){
    ids <- cl_cpos2id("REUTERS", p_attribute = "word", cpos = row[1]:row[2])
    tokens <- cl_id2str("REUTERS", p_attribute = "word", id = ids)
    paste(tokens, collapse = " ")
  }
 )

RcppCWB documentation built on Aug. 11, 2018, 1:04 a.m.